Neuromuscular Disorders

Many neuromuscular diseases cause dysphagia; in fact, the presenting symptom is often dysphagia. This is not surprising, considering the complex neuromuscular coordination required to execute a normal swallow. Although stroke patients develop sudden dysphagia, patients with other degenerative and nondegenerative neuromuscular diseases have a more insidious onset of dysphagia. Motor neuron diseases causing bulbar palsy or pseudobulbar palsy usually develop a progressive dysphagia and dysarthria with little upper or lower extremity involvement. Patients with myopathies must be identified early, because they have potentially treatable disorders.

Amyotrophic lateral sclerosis (ALS) has an incidence of around two per 100,000 with a usual age of onset in the sixth decade, although earlier onset is not uncommon. The incidence in men is slightly greater than in women. The typical symptom profile on onset is that of progressive, painless weakness. The symptoms that prompt evaluation by a physician are usually slurred speech or dysphagia. At least three-fourths of ALS patients will develop significant dysphagia before requiring ventilatory support, and detailed questioning will usually reveal that all patients have some dysphagia (7). The diagnosis requires the presence of both lower and upper motor neuron signs and progression of the disorder. Electromyography is an invaluable tool in the diagnosis. Tongue fasciculations at rest are almost pathognomonic for ALS; however, a thorough neurologic workup must be performed to exclude other disorders or neoplasms.

The inflammatory myopathies include dermatomyositis, polymyositis, and inclusion body myositis. These three disorders are characterized by inflammation and degeneration of skeletal muscle tissue and are thought to be autoimmune-mediated disorders. Although related in etiology, each has a characteristic clinical presentation. Dermatomyositis affects both children and adults. It is characterized by a patchy, discolored rash on the face, neck, shoulders, upper chest, elbows, knees, knuckles, and back that precedes muscle weakness. The most common symptom is a severe proximal muscle weakness, producing difficulty standing up, climbing stairs, lifting objects, and raising the arms above shoulder level. Dysphagia occurs in approximately one-third of all patients. Polymyositis also has as its most common symptom a proximal muscle weakness, although there is also a variable degree of involvement of the distal musculature and no associated rash. Dysphagia is equally common in polymyositis as in dermatomyositis. The dysphagia is primarily a result of increased pharyngeal transit time (8). Treatment for both polymyositis and dermatomyositis is with immunosuppressives such as prednisone, azathioprine, metho-trexate, and intravenous immunoglobulin. Inclusion myositis is very similar to polymyositis in that it is characterized by a slow and relentless progressive weakness. Symptoms usually begin after the age of 50 and are also associated with more atrophy and a greater involvement of distal musculature than in polymyositis. Current treatment for inclusion body myositis is supportive because it is unresponsive to immunosuppressive drugs. These conditions are discussed further in Chapter 1.

Duchenne muscular dystrophy (DMD) is the most common childhood form of muscular dystrophy. The typical age of onset is two to six years. The early signs of DMD include frequent falling, difficulty getting up, and a waddling gait. The disease first affects the pelvic muscles, upper arms, and upper legs. By the age of 12, virtually all patients suffer dysphagia; by the age of 18, severe dysphagia and aspiration are common. The dysphagia of DMD is characterized by pronounced oral and pharyngeal muscular weakness. Oculopharyngeal muscular dystrophy (OPMD) is characterized by a gradual onset of dysphagia, ptosis, and facial weakness. OPMD is an autosomal-dominant disorder with an age of onset in the fourth and fifth decade. Dysphagia is often the presenting symptom. Patients with OPMD have poor pharyngeal peristalses, poor upper esophageal sphincter (UES) relaxation, and low lower esophageal sphincter (LES) pressures. Cricopharyngeal myotomy or UES dilation may be effective in temporarily improving dysphagia in these patients; however, the long-term prognosis is unchanged after intervention (9). Spinal muscular atrophies (SMAs) comprise a group of neuromuscular disorders with varied clinical presentations, most of which occur early in childhood. Over one-third of patients with SMAs suffer from dysphagia.

Myasthenia gravis (MG) is characterized by the gradual progression of weakness over several weeks to months. The weakness tends to progress throughout the day and is worsened with physical exertion. MG is an autoimmune disorder in which antibodies to acetylcholine receptors bind to the receptors on the postsynaptic membrane of the neuromuscular junction, causing internalization and degradation of the receptors. Dysphagia is the presenting sign in 6% to 15% of adult patients (10). Bulbar and facial muscles are often affected and those patients with bulbar involvement typically have worse dysphagia and often aspirate. Treatment initially consists of medication with Mestinon (pyridostigmine), an acetylcholinesterase inhibitor, and possibly thymectomy. As disease progresses, some patients are offered plasmapheresis. Swallowing function varies as muscle function varies, so patients should be encouraged to eat early in the day and after medication.

Parkinson's disease is a progressive degenerative disorder caused by the degeneration of dopamine-containing neurons in the substantia nigra. The resulting disorder is characterized by rigidity and resting tremor. The rigidity is caused by simultaneous contraction of agonist and antagonist muscle groups that are usually coordinated to produce fine muscle movements. The resulting dysphagia is a result of poor bolus transport during the oral phase, early spill into the pharynx, and a prolonged pharyngeal transit time. The frequent pneumonias caused by aspiration are one of the most common causes of death in patients with Parkinson's disease (11). Other manometric abnormalities include poor UES relaxation, open LES, delayed transport, and tertiary contractions (12). Treatment with dopaminergic agents for Parkinson's disease can improve the dysphagia, but as the disease progresses, medication becomes less and less effective.

Progressive supranuclear palsy (PSP) is a progressive degenerative extrapyramidal disease that often mimics Parkinson's disease. The age of onset is typically one to two decades younger than in Parkinson's patients. Other differentiating characteristics include bilateral supranuclear ophthalmoplegia and lack of response to dopaminergic agents. PSP patients usually suffer from a worse dysphagia than Parkinson' s patients do. Unfortunately, no treatment is effective at improving this.

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