GALE ENCYCLOPEDIA OF NEUROLOGICAL DISORDERS 651 Paroxysmal hemicrania The growth factor, called GDNF, has been shown to slow cell death in experimental systems. A small group of pa- tients undergoing this surgery has improved, although these results are quite preliminary. Prognosis PD is a progressive disease, and the loss of brain tis- sue in the SN is inevitable. PD patients tend to live almost as long as age-matched individuals without PD, although with an increasing level of disability. Loss of motor con- trol can lead to an increased risk for falls, and swallowing difficulty can cause choking or aspiration (inhaling) of food. Aspiration pneumonia is a common cause of death in late-stage PD patients. Resources BOOKS Cram, David L. Understanding Parkinson’s Disease: A Self- Help Guide. Milford, CT: LPC, 1999. Hauser, Robert, and Theresa Zesiewicz. Parkinson’s Disease: Questions and Answers, 2nd edition. Coral Springs, FL: Merit Publishing International, 1997. Jahanshahi, Marjan, and C. David Marsden. Parkinson’s Disease: A Self-Help Guide. San Diego: Demos Medical Publishing, 2000. WEBSITES WE MOVE. <http://www.wemove.org> (April 27, 2004). Parkinson’s Disease Foundation. <http://www.pdf.org> (April 27, 2004). Richard Robinson ❙ Paroxysmal hemicrania Definition Paroxysmal hemicrania (PH) is a rare form of headache. Paroxysmal hemicrania usually begins in adulthood, and affected persons experience severe throb- bing, claw-like, or boring pain. The pain is usually on one side of the face, near or in the eye, temple, and occasion- ally reaching to the back of the neck. Red and tearing eyes, a drooping or swollen eyelid on the affected side of the face, and nasal congestion may accompany this pain. Per- sons experiencing the headache pain of paroxysmal hem- icrania may also feel dull pain, soreness, or tenderness between attacks. Description Paroxysmal hemicrania syndromes have two forms: chronic, in which persons experience attacks on a daily basis for a year or more, and episodic, in which the headaches do not occur for months or years. Episodic paroxysmal hemicrania is four times more common than the chronic form. Chronic paroxysmal hemicrania (CPH), also known as Sjaastad syndrome, is a primary headache disorder first described by the Norwegian neurologist Ottar Sjaastad in 1974. In 1976, Sjaastad proposed the term chronic parox- ysmal hemicrania after observing two patients, who had daily, solitary, severe headache pain that remained on one side of the head. The main feature of chronic paroxysmal hemicrania is frequent attacks of strictly one-sided severe pain localized in or around the eye or temple regions, last- ing from 2–45 minutes in duration, and occurring 2–40 times per day. Attacks of chronic paroxysmal hemicrania do not occur in recognizable time patterns. Episodic paroxysmal hemicrania (EPH), a more rare form of the disorder, is characterized by bouts of frequent, daily attacks with the same clinical features of CPH, but separated by relatively long periods without headache. Most episodic headaches in paroxysmal hemicrania occur at night or other recog- nizable time patterns. Demographics In the United States, CPH is a rare syndrome, but the number of diagnosed cases is increasing. The prevalence of CPH is not known, but it occurs more often than clus- ter headaches, a disorder of that can sometimes be con- fused with CPH. Internationally, many cases of CPH have been described throughout the world, in different races and different countries. Chronic paroxysmal hemicrania affects more women than men. In the past, because of female preponderance, CPH was considered a disease exclusive to women. How- ever, CPH has been reported in increasing numbers of men. A study conducted in 1979 reported a female-to- male ratio of 7:1, but a review of 84 patients in 1989 re- ported a female-to-male ratio of 2.3:1. Chronic paroxysmal hemicrania can occur at any age, and the mean age of onset is 34 years. Episodic paroxysmal hemicrania occurs in both sexes, with a slight female preponderance (1.3:1). The age of onset is variable; studies show EPH onset is 12–51 years. Causes and symptoms No definite cause of paroxysmal hemicrania is known. Persons who experience these headaches usually do not have additional neurological disorders, with the ex- ception of trigeminal neuralgia, which has been observed in a small number of persons also having paroxysmal hemicrania. History of head or neck trauma is reported in about 20% of persons with paroxysmal hemicrania, but LetterP.qxd 10/1/04 11:07 AM Page 651 652 GALE ENCYCLOPEDIA OF NEUROLOGICAL DISORDERS Paroxysmal hemicrania Key Terms Cluster headache A painful recurring headache associated with the release of histamine from cells. Migraine A severe recurring vascular headache; occurs more frequently in women than men. Trigeminal neuralgia A condition resulting from a disorder of the trigeminal nerve resulting in severe facial pain. these findings are similar to cluster headache or migraine headaches. Occasionally, attacks may be provoked me- chanically by bending or rotating the head and by apply- ing external pressure against the back of the neck. There is no inheritable pattern or familial disposition known for paroxysmal hemicrania, and affected individuals do not have a higher incidence of other types of headaches, such as CH or migraine, than the general population. Headache is the main symptom of both types of paroxysmal hemicrania. Chronic PH involves headaches that are one-sided, severe, affecting the eye or temple area, and lasting two to 45 minutes, occurring more than five times per day. Episodic paroxysmal hemicrania involves attacks of severe pain in the eye or temple area that last about one to 30 minutes, with a frequency of three or more events per day, and clear intervals between bouts of attacks that may last from months to years. Both chronic and episodic paroxysmal hemicrania in- volve symptoms such as nasal congestion on the affected side, rhinorrhea (runny nose), and swelling of the eyelid on the affected side with tearing. Sweating, both on the forehead and generalized over the body, is also common. Diagnosis The diagnosis of paroxysmal hemicrania is based on a person’s history and clinical symptoms. There are con- ditions involving underlying lesions in the brain (such as tumors or arteriovenous malformation) that can lead to symptoms similar to the headaches of paroxysmal hemi- crania. Because of this, various tests of the brain are rec- ommended to exclude structural abnormalities. Laboratory studies such as routine blood tests can help identify metabolic and other causes of headache and facial pain. Imaging studies including computed tomography (CT) scan, or preferably magnetic resonance imaging (MRI) of the brain may be needed to rule out structural disorders of the eye, ear, nose, neck, skull, and brain. Testing the effectiveness of the drug indomethiacin may also be a useful tool in the assessment of one-sided headaches. The response to indomethacin is part of the cri- teria for a diagnosis of paroxysmal hemicrania. During two different periods, the drug is administered intramus- cularly, and patterns of headache pain are evaluated. In paroxysmal hemicranias, indomethiacin relieves pain, pre- vents recurring pain, and/or decreases the frequency of pain. As the effects of indomethacin clear the body, the pain returns in its usual form and pattern. Treatment team A neurologist is the primary consultant for PH treat- ment. An ophthalmologist is also important to evaluate any eye disorders such as glaucoma. Treatment The nonsteroidal anti-inflammatory drug (NSAID) indomethacin often provides complete relief from symp- toms. Other less effective NSAIDs, calcium-channel blocking drugs (such as verapamil), and corticosteroids may be used to treat the disorder. Patients with both PH and trigeminal neuralgia (a condition of the fifth cranial nerve that causes sudden, severe pain typically felt on one side of the jaw or cheek) should receive separate treatment for each disorder. Recovery and rehabilitation When headaches are severe enough or frequent enough to interfere with a person’s daily activities such as work, family life, and home responsibilities, a specially trained physical therapist can provide a variety of treat- ment and education services to manage or reduce headaches, including: • exercises (stretching, strengthening, and aerobic condi- tioning) • safe sleep, standing, and sitting postures • performing daily activities safely • relaxation Clinical trials As of mid-2004, there were no ongoing clinical tri- als specific to the study or treatment of paroxysmal hem- icrania. The National Institute for Neurological Disorders and Stroke (NINDS), however, carries out multifaceted re- search on headaches and their causes. Prognosis Many patients experience complete relief or near- complete relief of symptoms following medical treatment for paroxysmal hemicrania. PH headaches may occur throughout life, but have also been known to go into re- mission or stop spontaneously. LetterP.qxd 10/1/04 11:07 AM Page 652 GALE ENCYCLOPEDIA OF NEUROLOGICAL DISORDERS 653 Parsonage-Turner syndrome Special concerns Chronic paroxysmal hemicrania headaches have been reported to improve during pregnancy; however, they often recur after delivery. In some persons, menstruation lessens the headaches, while in others, headaches are worse during menstruation. Birth control pills do not seem to influence the frequency of attacks, and the effects of menopause on paroxysmal hemicrania are unknown. Resources BOOKS Paulino, Joel, and Ceabert J. Griffith. The Headache Sourcebook. New York: McGraw-Hill/Contemporary Books, 2001. PERIODICALS Antonaci, F. “Chronic Paroxysmal Hemicrania and Hemicrania Continua. Parenteral Indomethacin: The ‘Indotest.’” Headache 38, no. 2 (February 1998): 122–128. Trucco, M., F. Maggioni, R. Badino, and G. Zanchin. “Chronic Paroxysmal Hemicrania, Hemicrania Continua and SUNCT Syndrome in Association with Other Pathologies: A Review.” Cephalalgia 24 (2004): 173–184. OTHER “NINDS Paroxysmal Hemicrania Information Page.” National Institute of Neurological Disorders and Stroke. May 8, 2004 (June 2, 2004). <http:// www.ninds.nih.gov/health_and_medical/disorders/ paroxysmal_hemicrania.htm>. ORGANIZATIONS American Council for Headache Education. 19 Mantua Road, Mt. Royal, NJ 08061. (856)423-0258 or (800) 255-ACHE (255-2243); Fax: (856) 423-0082. achehq@talley.com. <http://www.achenet.org>. National Headache Foundation. 820 N. Orleans, Suite 217, Chicago, IL 60610-3132. (773) 388-6399 or (888) NHF- 5552 (643-5552); Fax: (773) 525-7357. info@ headaches.org. <http://www.headaches.org>. Greiciane Gaburro Paneto Iuri Drumond Louro, MD, PhD ❙ Parsonage-Turner syndrome Definition Parsonage-Turner syndrome (PTS) is a rare syndrome of unknown cause, affecting mainly the lower motor neu- rons of the brachial plexus. The brachial plexus is a group of nerves that conduct signals from the spine to the shoul- der, arm, and hand. PTS is usually characterized by the sudden onset of severe one-sided shoulder pain, followed by paralysis of the shoulder and lack of muscle control in the arm, wrist, or hand several days later. The syndrome can vary greatly in presentation and nerve involvement. Description PTS, also known as brachial plexus neuritis or neu- ralgic amyotrophy, is a common condition characterized by inflammation of a network of nerves that control and supply (innervate) the muscles of the chest, shoulders, and arms. Individuals with the condition first experience se- vere pain across the shoulder and upper arm. Within a few hours or days, weakness, wasting (atrophy), and paralysis may affect the muscles of the shoulder. Although individ- uals with the condition may experience paralysis of the af- fected areas for months or, in some cases, years, recovery is usually eventually complete. Local pain around the shoulder girdle is the prevalent symptom of Parsonage-Turner syndrome. It is usually sud- den and often severe, often awakening persons during the night. The pain worsens progressively for up to two days. Described as a constant, severe ache associated with ten- derness of the muscles, the pain is not affected by cough- ing. However, it is accentuated by arm movements and muscular pressure, but almost unaltered by movements of the neck. The pain is commonly distributed across the back of the scapula (shoulder blade) and the tip of the shoulder. Pain often radiates down the outer side of the arm and up along the neck, and seldom spreads down as far as the outer side of the forearm, below the elbow. There is no exact correlation between the localization of the pain and the distribution of the subsequent muscle paralysis. However, in general, pain radiating below the elbow is associated with involvement of the biceps or triceps, and radiation into the neck involves the sternocleidomastoid and trapezius muscles. Usually the severe pain lasts from a few hours to three weeks and then disappears rather sud- denly; at the same time, muscular wasting and weakness are occurring. A less severe pain may persist considerably longer. As the pain subsides, paralysis of some muscles of the shoulder girdle, and often of the arm, develops. Usually, muscle weakness appears suddenly, but sometimes grad- ually increases over two or three days, or up to one week in rare cases. The paralysis involves limpness and rapid wasting of the affected muscles. Tendon reflexes might be affected, depending on the severity and extent of muscu- lar paralysis and wasting. Weakened reflexes are fre- quently encountered, and fasciculations (fine tremors) occasionally occur. Demographics In the United States, the incidence is approximately 1.64 cases per 100,000 people per year. Internationally, PTS has been described in many countries around the LetterP.qxd 10/1/04 11:07 AM Page 653 654 GALE ENCYCLOPEDIA OF NEUROLOGICAL DISORDERS Parsonage-Turner syndrome Key Terms Atrophy Degeneration or wasting of tissues. Brachial plexus A group of nerves that exit the cervical (neck) and upper thoracic (chest) spinal column to provide muscle control to the shoulder, arms, and hands. Scapula The bone also known as the shoulder blade. Trapezius Muscle of the upper back that rotates the shoulder blade, raises the shoulder, and flexes the arm. Triceps Muscle of the back of the upper arm, pri- marily responsible for extending the elbow. world, although specific rates of incidence have not been reported. There is a male predominance in PTS with a male-to-female ratio ranging from 2:1–4:1. Individuals as young as three months or as old as 74 years can be affected with PTS; however, the prevalence is highest in young to middle-aged adults. When a child develops Parsonage- Turner syndrome, hereditary PTS should be considered. Causes and symptoms The exact cause of PTS is unknown, but the condi- tion has been linked to many previous events or illnesses such as: • viral infection (particularly of the upper respiratory tract) • bacterial infection (e.g., pneumonia, diphtheria, typhoid) • parasitic infestation • surgery • trauma (not related to shoulder) • vaccinations (e.g., influenza, tetanus, diphtheria, tetanus toxoids, pertussis, smallpox, swine flu) • childbirth • miscellaneous medical investigative procedures (e.g., lumbar puncture, administration of radiologic dye) • systemic illness (e.g., polyarteritis nodosa, lymphoma, systemic lupus erythematosus, temporal arteritis, Ehlers-Danlos syndrome) In addition to these possible causes, a rare hereditary form of PTS has been localized to a defect on chromo- some 17, and should be considered a distinct disorder. This form of the disorder occurs in a younger age group, affects males and females equally (autosomal-dominant inheri- tance), and is characterized by recurrent attacks that often cause pain on both sides of the body. Acute pain in the shoulder girdle or arm is almost al- ways the first symptom. Shortly thereafter, muscle weak- ness and wasting in the shoulder girdle and arm occur. The pain, which may be extraordinarily severe for a short time, eventually abates. Diagnosis PTS is a clinical syndrome, and therefore diagnosis is made by exclusion. Other disorders of the upper extrem- ity or cervical spine have to be excluded, including ab- normalities of the rotator cuff, acute calcific tendinitis, adhesive capsulitis, cervical radiculopathy, peripheral nerve compression, acute poliomyelitis, and amy- otrophic lateral sclerosis (ALS). PTS may sometimes be confused with peripheral nerve compression or traction in- jury of the brachial plexus. Affected persons, however, do not experience the acute intense pain associated with PTS, and the loss of strength occurs simultaneously with the sensory changes. In PTS, x rays of the cervical spine and shoulder show normal findings compatible with the patient’s age. Nerve conduction studies and electromyography (EMG) are helpful in localizing the lesion. Three to four weeks after the onset of pain, EMG studies show changes consistent with PTS. Arthrography or ultrasound may be useful to rule out a tear of the rotator cuff. MRI may reveal muscles changes associated with PTS. Treatment team A specialist in neuromuscular disease may be con- sulted to confirm diagnosis and evaluate any potentially underlying causes. An orthopedic surgeon is important when nerve grafting or tendon transfer is necessary. Phys- ical and occupational therapists may be asked to provide a comprehensive rehabilitation program. Treatment No specific treatment has yet been proved efficient in PTS. In the early stages, pain may require treatment. Com- mon analgesic drugs are usually sufficient. Usually, steroidal medications do not relieve the pain or improve muscle function in PTS. Rest is recommended, and im- mobilization of the affected upper extremity may be help- ful in relieving the pain and in preventing stretching of the affected muscles. As pain subsides, physical therapy is recommended. Passive range of motion exercises of the shoulder and elbow are suggested to maintain full range of motion. Surgical stabilization of the scapula to the thorax, or tendon transfers have been performed with benefit in per- sons with PTS who experience continuing pain and mus- cle weakness. LetterP.qxd 10/1/04 11:07 AM Page 654 GALE ENCYCLOPEDIA OF NEUROLOGICAL DISORDERS 655 Perineural cysts Recovery and rehabilitation Physical therapy should focus on the maintenance of full range of motion (ROM) in the shoulder and other af- fected joints. Passive range of motion (PROM) and active range of motion (AROM) exercises should begin as soon as the pain has been controlled adequately, followed by re- gional conditioning of the affected areas. Strengthening of the rotator cuff muscles and scapular stabilization may be indicated. Passive modalities (e.g., heat, cold, transcuta- neous electrical nerve stimulation) may be useful as ad- junct pain relievers. Another type of rehabilitation therapy in PTS is oc- cupational therapy. Functional conditioning of the upper extremity may be helpful. Assistive devices and orthotics (such as splints or devices for grasping and reaching) may be used, depending on the particular disabilities present. Clinical trials As of mid-2004, there were no ongoing clinical tri- als specific for PTS. Prognosis The overall prognosis for persons with PTS is good, as recovery of strength and sensation usually begins spon- taneously as early as one month after the onset of symp- toms. Almost 75% of persons with PTS experience complete recovery within two years. However, the period of time for complete recovery is variable, ranging from six months to five years. It seems that the delay in recovering strength depends on the severity and duration of pain, weakness, or both. Furthermore, patients with involvement of upper trunk lesions have the most rapid recovery. Al- though not very common, relapse might occur within a few months to several years after full recovery. In general, complete restoration of normal strength and function usu- ally occurs within five years. Resources BOOKS Liverson, Jay Allan. Peripheral Neurology: Case Studies. Oxford, UK: Oxford University Press, 2000. PERIODICALS Parsonage, M. J., and J. W. Aldren Turner. “Neuralgic Amyotrophy. The Shoulder-Girdle Syndrome.” Lancet 1948, I: 973–1,978. Simon, J. P. A., and G. Fabry. “Parsonage-Turner Syndrome after Total-Hip Arthroplasty.” The Journal of Arthroplasty 16 (2001): 518–520. OTHER “Parsonage-Turner Syndrome.” Yale New Haven Health. May 6, 2004 (June 2, 2004). <http://yalenewhaven health.org/library/healthguide/IllnessConditions/ topic.asp?hwid=nord726>. ORGANIZATIONS American Autoimmune Related Diseases Association. 22100 Gratiot Avenue, Eastpointe, MI 48021. (586) 776-3900. aarda@aarda.org. <http://www.aarda.org/>. NIH/National Arthritis and Musculoskeletal and Skin Diseases Information Clearinghouse. 1 AMS Circle, Bethesda, MD 20892-3675. (301) 495-4484 or (877) 226-4267. niamsinfo@mail.nih.gov. <http://www.niams.nih.gov>. Greiciane Gaburro Paneto Iuri Drumond Louro Pellegra see Vitamin/nutritional deficiency Pemoline see Central nervous system stimulants ❙ Perineural cysts Definition Perineural cysts (also called Tarlov cysts) are abnor- mal fluid-filled sacs located in the sacrum, the base of the spine. Description Perineural cysts appear to be dilated or ballooned areas of the sheaths that cover nerve roots exiting from the sacral area of the spine. The spaces or cysts created by the dilated sheaths are directly connected to the subarachnoid area of the spinal column, the area through which cere- brospinal fluid flows. Many people have perineural cysts but no symptoms at all; in fact, the majority of people with these cysts are completely unaware of their existence. However, when conditions cause these perineural cysts to fill with cerebrospinal fluid and expand in size, they can begin to compress important neighboring nerve fibers, re- sulting in a variety of symptoms, including pain, weak- ness, and abnormal sensation. Demographics More women than men develop perineural cysts. Causes and symptoms A variety of conditions that can increase the flow of cerebrospinal fluid may cause perineural cysts to expand in size, creating symptoms. Such conditions include trau- matic injury, shock, or certain forms of exertion (such as heavy lifting) or exercise. Prolonged sitting or standing may cause cysts to fill and retain fluid. Other research sug- gests that herpes simplex virus can cause the body chem- istry to become more alkaline, which predisposes the LetterP.qxd 10/1/04 11:07 AM Page 655 656 GALE ENCYCLOPEDIA OF NEUROLOGICAL DISORDERS Periodic paralysis Key Terms Cerebrospinal fluid A fluid that bathes the brain and the spinal cord. Cyst A fluid-filled sac. Sacrum An area in the lower back, below the lumbar region. Subarachnoid The space underneath the layer of meningeal membrane called the arachnoid. cerebrospinal fluid to fill the perineural cysts, thus prompting the advent of symptoms. The symptoms of expanding perineural cysts occur due to compression of nerve roots that exit from the sacral area. Symptoms may include back pain and sciatica,a syndrome of symptoms that occur due to compression or inflammation of the sciatic nerve. Sciatica results in burn- ing, tingling, numbness, stinging, or electric shock sensa- tions in the lower back, buttocks, thigh, and down the leg to below the knee. Severe sciatica may also result in weak- ness of the leg or foot. Other more severe symptoms of perineural cysts include loss of bladder control and prob- lems with sexual functioning. Diagnosis Because most perineural cysts don’t cause symptoms, most perineural cysts are never diagnosed. When symp- toms do develop that are suggestive of perineural cysts, MRI will usually demonstrate their presence, and CT myelography (a test in which dye is injected into the spine) may demonstrate the cerebrospinal fluid flow between the spinal subarachnoid area and the cyst. Treatment team Neurologists and neurosurgeons usually treat indi- viduals with perineural cysts. A urologist may be called in to consult with individuals whose cysts are interfering with bladder or sexual functioning. Treatment Although using a needle to drain fluid from perineural cysts can temporarily relieve their accompanying symp- toms, eventually the cysts will refill with cerebrospinal fluid and the symptoms will recur. Similarly, steroid in- jections can provide short-term pain relief. Pain may also be temporarily controlled by injecting the cysts with fib- rin glue (a substance produced from blood chemicals in- volved in the clotting mechanism). Using diet or dietary supplements to decrease the body’s alkalinity may prevent perineural cysts from filling with more fluid. Medications used to treat chronic nerve-related pain (such as anticon- vulsants and antidepressants) may be helpful. When pain is intractable despite a variety of inter- ventions, or when weakness or other neurological symp- toms become severe, surgery to remove the cysts may be necessary. This is the only permanent treatment for per- ineural cysts; once removed, they very rarely recur. Prognosis Most individuals with perineural cysts have no symptoms whatsoever. Those who do have symptoms run a risk of neurological damage if the cysts continue to com- press nerve structures over time. Individuals who undergo neurosurgery to remove the cysts usually have an excellent outcome, with no cyst recurrence. Resources BOOKS Braunwald, Eugene, et al., eds. Harrison’s Principles of Internal Medicine. NY: McGraw-Hill Professional, 2001. Goetz, Christopher G., ed. Textbook of Clinical Neurology. Philadelphia: W. B. Saunders Company, 2003. Goldman, Lee, et al., eds. Cecil Textbook of Internal Medicine. Philadelphia: W. B. Saunders Company, 2000. PERIODICALS Acosta, Frank L., et al. “Diagnosis and Management of Sacral Tarlov cysts.” Neurosurgical Focus 15, no. 2 (August 2003). Available online at <http://www.aans.org/educa- tion/journal/neurosurgical/aug03/15-2-15.pdf> (June 3, 2004). Voyadzis, J. M., et al. “Tarlov cysts: a study of 10 cases with review of the literature.” Journal of Neurosurgery 95 (July 2001): 25–32. WEBSITES National Institute of Neurological Disorders and Stroke (NINDS). NINDS Tarlov Cysts Information Page. July 10, 2003. <http://www.ninds.nih.gov/health_and_medical/ disorders/tarlov_cysts.htm> (June 3, 2004). Tarlov Cyst Support Group. <http://www.tarlovcyst.net/> (June 3, 2004). Rosalyn Carson-DeWitt, MD ❙ Periodic paralysis Periodic paralysis (PP) is the name for several rare, inherited muscle disorders marked by temporary weak- ness, especially following rest, sleep, or exercise. LetterP.qxd 10/1/04 11:07 AM Page 656 GALE ENCYCLOPEDIA OF NEUROLOGICAL DISORDERS 657 Periodic paralysis Key Terms Gene A biologic unit of heredity transmitted from parents to offspring. Description Periodic paralysis disorders are genetic disorders that affect muscle strength. There are two major forms, hy- pokalemic and hyperkalemic, each caused by defects in different genes. In hypokalemic PP, the level of potassium in the blood falls in the early stages of a paralytic attack, while in hyperkalemic PP, it rises slightly or is normal. (The root of both words, “kali,” refers to potassium.) Hyperkalemic PP is also called potassium-sensitive PP. Causes and symptoms Both forms of PP are caused by inheritance of defec- tive genes. Both genes are dominant, meaning that only one copy of the defective gene is needed for a person to develop the disease. A parent with the gene has a 50% chance of passing it along to each offspring, and the like- lihood of passing it on is unaffected by the results of pre- vious pregnancies. The gene for hypokalemic PP is present equally in both sexes, but leads to noticeable symptoms more often in men than in women. The normal gene is responsible for a muscle protein controlling the flow of calcium during muscle contraction. The gene for hyperkalemic PP affects virtually all who inherit it, with no difference in male-vs female expression. The normal gene is responsible for a muscle protein con- trolling the flow of sodium during muscle contraction. The attacks of weakness in hypokalemic PP usually begin in late childhood or early adolescence and often be- come less frequent during middle age. The majority of pa- tients develop symptoms before age 16. Since they begin in the school years, the symptoms of hypokalemic PP are often first seen during physical education classes or after- school sports, and may be mistaken for laziness, or lack of interest on the part of the child. Attacks are most commonly brought on by: • strenuous exercise followed by a short period of rest • large meals, especially ones rich in carbohydrates or salt • emotional stress • alcohol use • infection • pregnancy The weakness from a particular attack may last from several hours to as long as several days, and may be local- ized to a particular limb, or might involve the entire body. The attacks of weakness of hyperkalemic PP usually begin in infancy or early childhood, and may also become less severe later in life. As in the hypokalemic form, at- tacks are brought on by stress, pregnancy, and exercise fol- lowed by rest. In contrast, though, hyperkalemic attacks are not associated with a heavy meal but rather with miss- ing a meal, with high potassium intake, or use of gluco- corticoid drugs such as prednisone. (Glucocorticoids are a group of steroids that regulate metabolism and affect muscle tone.) Weakness usually lasts less than three hours, and often persists for only several minutes. The attacks are usually less severe, but more frequent, than those of the hypokalemic form. Weakness usually progresses from the lower limbs to the upper, and may involve the facial mus- cles as well. Diagnosis Diagnosis of either form of PP begins with a careful medical history and a complete physical and neurological exam. A family medical history may reveal other affected relatives. Blood and urine tests done at the onset of an at- tack show whether there are elevated or depressed levels of potassium. Electrical tests of muscle and a muscle biopsy show characteristic changes. Challenge tests, to aid in diagnosis, differ for the two forms. In hypokalemic PP, an attack of weakness can be brought on by administration of glucose and insulin, with exercise if necessary. An attack of hyperkalemic PP can be induced with administration of potassium after exercise during fasting. These tests are potentially hazardous and require careful monitoring. Genetic tests are available at some research centers and are usually recommended for patients with a known family history. However, the number of different possible mutations leading to each form is too great to allow a sin- gle comprehensive test for either form, thus limiting the usefulness of genetic testing. Treatment Severe respiratory weakness from hypokalemic PP may require intensive care to ensure adequate ventilation. Potassium chloride may be given by mouth or intra- venously to normalize blood levels. Attacks requiring treatment are much less common in hyperkalemic PP. Glucose and insulin may be prescribed. Eating carbohydrates may also relieve attacks. LetterP.qxd 10/1/04 11:07 AM Page 657 658 GALE ENCYCLOPEDIA OF NEUROLOGICAL DISORDERS Peripheral nervous system Prognosis Most patients learn to prevent their attacks well enough that no significant deterioration in the quality of life occurs. Strenuous exercise must be avoided, however. Attacks often lessen in severity and frequency during mid- dle age. Frequent or severe attacks increase the likelihood of permanent residual weakness, a risk in both forms of periodic paralysis. Prevention There is no way to prevent the occurrence of either disease in a person with the gene for the disease. The like- lihood of an attack of either form of PP may be lessened by avoiding the triggers (the events or combinations of cir- cumstances which cause an attack) for each. Hypokalemic PP attacks may be prevented with use of acetazolamide (or another carbonic anhydrase in- hibitor drug) or a diuretic to help retain potassium in the bloodstream. These attacks may also be prevented by avoiding such triggers as salty food, large meals, a high- carbohydrate diet, and strenuous exercise. Attacks of hyperkalemic PP may be prevented with frequent small meals high in carbohydrates, and the avoid- ance of foods high in potassium such as orange juice or bananas. Acetazolamide or thiazide (a diuretic) may be prescribed. Resources BOOKS Harrison’s Principles of Internal Medicine. Anthony S. Fauci, et al., eds. New York: McGraw-Hill, 1997. Greenberg, David A., et al. Clinical Neurology. 2nd ed. Norwalk, CT: Appleton & Lange, 1993. ORGANIZATIONS Muscular Dystrophy Association. 3300 East Sunrise Drive, Tucson, AZ 85718. (800) 572-1717. <http:// www.mdausa.org>. The Periodic Paralysis Association. 5225 Canyon Crest Drive #71-351, Riverside, CA 92507. (909) 781-4401. <http:// www.periodicparalysis.org>. Richard Robinson ❙ Peripheral nervous system Definition The peripheral nervous system (PNS) consists of all parts of the nervous system, except the brain and spinal cord, which are the components of the central nervous system (CNS). The peripheral nervous system connects the central nervous system to the remainder of the body, and is the conduit through which neural signals are trans- mitted to and from the central nervous system. Within the peripheral nervous system, sensory neurons transmit im- pulses to the CNS from sensory receptors. A system of motor neurons transmit neural signals from the CNS to ef- fectors (glands, organs, and muscles). Description The peripheral nervous system is composed of nerve fibers that provide the cellular pathways for the various signals on which the proper operation of the nervous sys- tem relies. There are two types of neurons operating in the PNS. The first is the sensory neurons that run from the myriad of sensory receptors throughout the body. Sensory receptors provide the connection between the stimulus such as heat, cold, and pain and the CNS. As well, the PNS also consists of motor neurons. These neurons con- nect the CNS to various muscles and glands throughout the body. These muscles and glands are also known as ef- fectors, meaning they are the places where the responses to the stimuli are translated into action. The peripheral nervous system is subdivided into two subsystems: the sensory-somatic nervous system and the autonomic nervous system. The sensory-somatic nervous system The sensory-somatic nervous system is the sensory gateway between the environment outside of the body and the central nervous system. Responses tend to be con- scious. The sensory nervous system comprises 12 pairs of cranial nerves and 31 pairs of spinal nerves. Some pairs are exclusively sensory neurons such as the pairs involved in smell, vision, hearing, and balance. Other pairs are strictly made up of motor neurons, such as those involved in the movement of the eyeballs, swallowing, and move- ment of the head and shoulders. Still other pairs consist of a sensory and a motor neuron working in tandem such as those involved in taste and other aspects of swallowing. All of the spinal neuron pairs are mixed: they contain both sensory and motor neurons. This allows the spinal neurons to properly function as the conduit of transmission of the signals of the stimuli and the subsequent response. The autonomic nervous system The autonomic nervous system (ANS) consists of three subsystems: the sympathetic nervous system, the parasympathetic nervous system, and the enteric nervous system. The ANS regulates the activities of cardiac mus- cle, smooth muscle, endocrine glands, and exocrine glands. The ANS functions involuntarily (i.e., reflexively) LetterP.qxd 10/1/04 11:07 AM Page 658 GALE ENCYCLOPEDIA OF NEUROLOGICAL DISORDERS 659 Peripheral nervous system Key Terms Central nervous system (CNS) Composed of the brain and spinal cord. Peripheral nervous system (PNS) All parts of the nervous system, except the brain and spinal cord. in an automatic manner without conscious control. Ac- cordingly, the ANS is the mediator of visceral reflex arcs. In contrast to the somatic nervous system that always acts to excite muscle groups, the autonomic nervous sys- tems can act to excite or inhibit innervated tissue. The au- tonomic nervous system achieves this ability to excite or inhibit activity via a dual innervation of target tissues and organs. Most target organs and tissues are innervated by neural fibers from both the parasympathetic and sympa- thetic systems. The systems can act to stimulate organs and tissues in opposite ways (antagonistically). For ex- ample, parasympathetic stimulation acts to decrease heart rate. In contrast, sympathetic stimulation results in in- creased heart rate. The systems can also act in concert to stimulate activity (e.g., both increase the production of saliva by salivary glands, but parasympathetic stimulation results in watery as opposed to viscous or thick saliva). The ANS achieves this control via two divisions of the ANS, the sympathetic nervous system and the parasym- pathetic nervous system. The autonomic nervous system also differs from the somatic nervous system in the types of tissue innervated and controlled. The somatic nervous system regulates skeletal muscle tissue, while the ANS services smooth muscle, cardiac muscle, and glandular tissue. Although the sympathetic systems share a number of common features (i.e., both contain myelinated pregan- glionic nerve fibers that usually connect with unmyeli- nated postganglionic fibers via a cluster of neural cells termed ganglia), the classification of the parasympathetic and the sympathetic systems of the ANS is based both on anatomical and physiological differences between the two subdivisions. The sympathetic nervous system The nerve fibers of the sympathetic system innervate smooth muscle, cardiac muscle, and glandular tissue. In general, stimulation via sympathetic fibers increases ac- tivity and metabolic rate. Accordingly, sympathetic sys- tem stimulation is a critical component of the fight or flight response. The cell bodies of sympathetic fibers traveling toward the ganglia (preganglionic fibers) are located in the tho- racic and lumbar spinal nerves. These thoraco-lumbar fibers then travel only a short distance within the spinal nerve (composed of an independent mixture of fiber types) before leaving the nerve as myelinated white fibers that synapse with the sympathetic ganglia that lie close to the side of the vertebral column. The sympathetic ganglia lie in chains that line both the right and left sides of the ver- tebral column, from the cervical to the sacral region. Por- tions of the sympathetic preganglionic fibers do not travel to the vertebral ganglionic chains, but travel instead to spe- cialized cervical or abdominal ganglia. Other variations are also possible. For example, preganglionic fibers can synapse directly with cells in the adrenal medulla. In contrast to the parasympathetic system, the pre- ganglionic fibers of the sympathetic nervous system are usually short, and the sympathetic postganglionic fibers are long fibers that must travel to the target tissue. The sympathetic postganglionic fibers usually travel back to the spinal nerve via unmyelineted or gray rami before con- tinuing to the target effector organs. With regard to specific target organs and tissues, sym- pathetic stimulation of the pupil dilates the pupil. The di- lation allows more light to enter the eye and acts to increase acuity in depth and peripheral perception. Sympathetic stimulation acts to increase heart rate and increase the force of atrial and ventricular contrac- tions. Sympathetic stimulation also increases the conduc- tion velocity of cardiac muscle fibers. Sympathetic stimulation also causes a dilation of systemic arterial blood vessels, resulting in greater oxygen delivery. Sympathetic stimulation of the lungs and smooth muscle surrounding the bronchi results in bronchial mus- cle relaxation. The relaxation allows the bronchi to expand to their full volumetric capacity and thereby allow greater volumes of air passage during respiration. The increased availability of oxygen and increased venting of carbon dioxide are necessary to sustain vigorous muscular activ- ity. Sympathetic stimulation can also result in increased activity by glands that control bronchial secretions. Sympathetic stimulation of the liver increases glycogenolysis and lipolysis to make energy more avail- able to metabolic processes. Constriction of gastrointesti- nal sphincters (smooth muscle valves or constrictions) and a general decrease in gastrointestinal motility assure that blood and oxygen needed for more urgent needs (such as fight or flight) are not wasted on digestive system processes that can be deferred for short periods. The fight or flight response is a physical response; a strong stimulus or emergency causes the release of a chemical called nor- adrenaline (also called norepinephrine) that alternately stimulates or inhibits the functioning of a myriad of glands LetterP.qxd 10/1/04 11:07 AM Page 659 660 GALE ENCYCLOPEDIA OF NEUROLOGICAL DISORDERS Peripheral nervous system and muscles. Examples include the acceleration of the heartbeat, raising of blood pressure, shrinkage of the pupils of the eyes, and the redirection of blood away from the skin to muscles, brain, and the heart. Sympathetic stimulation results in renin secretion by the kidneys and causes a relaxation of the bladder. Ac- companied by a constriction of the bladder sphincter, sym- pathetic stimulation tends to decrease urination and promote fluid retention. Acetylcholine is the neurotransmitter most often found in the sympathetic preganglionic synapse. Although there are exceptions (e.g., sweat glands utilize acetyl- choline), epinephrine (noradrenaline) is the most common neurotransmitter found in postganglionic synapses. The parasympathetic nervous system Parasympathetic fibers innervate smooth muscle, car- diac muscle, and glandular tissue. In general, stimulation via parasympathetic fibers slows activity and results in a lowering of metabolic rate and a concordant conservation of energy. Accordingly, the parasympathetic nervous sub- system operates to return the body to its normal levels of function following the sudden alteration by the sympa- thetic nervous subsystem; the so-called “rest and digest” state. Examples include the restoration of resting heart- beat, blood pressure, pupil diameter, and flow of blood to the skin. The preganglionic fibers of the parasympathetic sys- tem derive from the neural cell bodies of the motor nuclei of the occulomotor (cranial nerve: III), facial (VII), glos- sopharyngeal (IX), and vagal (X) cranial nerves. There are also contributions from cells in the sacral segments of the spinal cord. These cranio-sacral fibers generally travel to a ganglion that is located near or within the target tissue. Because of the proximity of the ganglia to the target tissue or organ, the postganglionic fibers are much shorter. Parasympathetic stimulation of the pupil from fibers derived from the occulomotor (cranial nerve: III), facial (VII), and glossopharyngeal (IX) nerves constricts or nar- rows the pupil. This reflexive action is an important safe- guard against bright light that could otherwise damage the retina. Parasympathetic stimulation also results in in- creased lacrimal gland secretions (tears) that protect, moisten, and clean the eye. The vagus nerve (cranial nerve: X) carries fibers to the heart, lungs, stomach, upper intestine, and ureter. Fibers derived from the sacrum innervate reproductive or- gans, portions of the colon, bladder, and rectum. With regard to specific target organs and tissues, parasympathetic stimulation acts to decrease heart rate and decrease the force of contraction. Parasympathetic stimu- lation also reduces the conduction velocity of cardiac mus- cle fibers. Parasympathetic stimulation of the lungs and smooth muscle surrounding the bronchi results in bronchial con- striction or tightening. Parasympathetic stimulation can also result in increased activity by glands that control bronchial secretions. Parasympathetic stimulation usually causes a dilation of arterial blood vessels, increased glycogen synthesis within the liver, a relaxation of gastrointestinal sphincters (smooth muscle valves or constrictions), and a general in- crease in gastrointestinal motility (the contractions of the intestines that help food move through the system). Parasympathetic stimulation results in a contracting spasm of the bladder. Accompanied by a relaxation of the sphincter, parasympathetic stimulation tends to promote urination. The chemical most commonly found in both pre- and postganglionic synapses in the parasympathetic system is the neurotransmitter acetylcholine. The enteric nervous system The enteric nervous system is made up of nerve fibers that supply the viscera of the body: the gastrointestinal tract, pancreas, and gallbladder. Regulation of the autonomic nervous system The involuntary ANS is controlled in the hypothala- mus, while the somatic system is regulated by other re- gions of the brain (cortex). In contrast, the somatic nervous system may control motor functions by neural pathways that contain only a single axon that innervates an effector (i.e., target) muscle. The ANS is comprised of pathways that must contain at least two axons separated by a ganglia that lies in the path between the axons. ANS reflex arcs are stimulated by input from sensory or visceral receptors. The signals are processed in the hy- pothalamus (or regions of the spinal cord) and target ef- fector control is then regulated via myelinated preganglionic neurons (cranial and spinal nerves that also contain somatic nervous system neurons). Ultimately, the preganglionic neurons terminate in a neural ganglion. Di- rect effector control is then regulated via unmyelinated postganglionic neurons. The principal neurotransmitters in ANS synapses are acetylcholine and norepinephrine. General PNS disorders General PNS disorders include loss of sensation or hyperesthesia (abnormal or pathological sensitivity). Sensations such as prickling or tingling without observ- able stimulus (paresthesia) or burning sensations are also abnormal. LetterP.qxd 10/1/04 11:07 AM Page 660 [...]... 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(856) 42 3 - 025 8 or (800) 25 5-ACHE (25 5 -2 2 43 ); Fax: (856) 42 3 -0 0 82. achehq@talley.com. <http://www.achenet.org>. National Headache Foundation. 820 N. Orleans, Suite 21 7, Chicago, IL 6061 0-3 1 32. . 5801, Bethesda, MD 20 8 24 . (800) 3 5 2- 9 42 4 . <http://www.ninds.nih.gov>. The Neuropathy Association. 60 E. 42 nd Street, Suite 9 42 , New York, NY 1016 5-0 999. (21 2) 6 9 2- 06 62. info@ neuropathy.org NIH Publication No. 01 -2 4 06. Bethesda, MD: NINDS, 20 01. ORGANIZATIONS American Chronic Pain Association. P.O. Box 850, Rocklin, CA 9567 7-0 850. (916) 6 3 2- 0 922 or (800) 53 3- 323 1; Fax: (916) 6 3 2- 320 8. ACPA@pacbell.net.