Oculopharyngeal Muscular Dystrophy

Oculopharyngeal muscular dystrophy is a disorder of late adult onset characterized by progressive ptosis and dysphagia. The region of chromosome 14q11.2-q13 with the cardiac and beta myosin heavy chain genes is the locus of the causative gene in three French Canadian families. y Although the highest prevalence of oculopharyngeal muscular dystrophy continues to be in Quebec, which is most likely the result of a founder effect, families have now been identified in more than 20 countries. Inheritance is autosomal dominant with complete penetrance.

Asymmetrical weakness of the levator palpebrae and pharyngeal muscles is the initial presentation, generally after the age of 50. Eventually all extraocular muscles may become involved. There is no cardiac involvement. The EMG shows myopathic changes. Muscle biopsy reveals changes found in other muscular dystrophies: loss of muscle fibers, variation in fiber size, increased numbers of nuclei and internal nuclei, and increased fibrous and fatty connective tissue. On histochemistry, there are small angulated fibers that react strongly for oxidative enzymes and "rimmed" vacuoles, particularly in type I fibers from extremity muscles rather than extraocular muscles. On electron microscopy, there are unique intranuclear tubular filaments. y

Oculopharyngeal muscular dystrophy can be distinguished from inclusion body myositis, which presents as dysphagia. It also has rimmed vacuoles, but the filaments seen are larger and are present in the cytoplasm as well as the nucleus and there are no ocular palsies. Ocular myasthenia gravis without waxing and waning of symptoms may produce weakness in the same distribution as oculopharyngeal muscular dystrophy, but it generates demonstrable neuromuscular junction transmission defects on EMG and neuromuscular junction abnormalities on morphological studies. Although late onset of the mitochondrial myopathy, Kearns-Sayre syndrome, or oculocraniosomatic disease may present with ptosis, histochemical and ultrastructural studies of muscle show biochemical defects in the respiratory chain and mitochondrial DNA deletions.

Interventions, such as eyelid crutches to alleviate the ptosis and a feeding tube to provide adequate nutrition, are palliative. If the patient does not receive a feeding tube, the dysphagia will lead to early death by malnutrition and starvation.

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