Facioscapulohumeral Muscular Dystrophy

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Facioscapulohumeral muscular dystrophy (FSH MD), or Landouzy-Dejerine muscular dystrophy, is slowly progressive degenerative myopathy that affects particular facial, torso, and extremity muscles. There are at least two loci for FSH MD. Most large families thus far are linked to 4q35, in which no gene has been found. About 15 percent of other clinically indistinguishable families remain unlinked. y Although isolated cases have been identified, generally

TABLE 36-6 -- DIFFERENTIAL DIAGNOSES IN LIMB GIRDLE MUSCULAR DYSTROPHY

Acid maltase deficiency

Fingerprint myopathy

Becker muscular dystrophy

Inclusion body myositis

Carnitine deficiency

McArdle's disease

Central core disease

Mitochondrial myopathy

Centronuclear myopathy

Multicore disease

Congenital fiber-type disproportion

Myopathy with tubular aggregates

Debrancher enzyme deficiency

Myopathy with cytoplasmic bodies

Duchenne muscular dystrophy

Nemaline rod disease

Duchenne manifesting earner

Reducing body myopathy

Emery-Dreifuss musculardystrophy

Sarcotubular myopathy

Scapuloperoneal dystrophy

Facioscapulohumeral dystrophy

Spinal muscular atrophy

with careful evaluation of the family, there is a clear autosomal dominant inheritance pattern with a penetrance of 95 percent by the time the individuals reach their 20s. Prevalence is about 1 in 20,000. d

Onset has been reported from infancy until middle age. There is significant variability of the severity symptoms within families, with some individuals having symptoms that are so mild that they are unaware they have the disease until other family members are diagnosed. Generally, the patient first notices asymmetrical weakness in an upper extremity, although facial weakness may have been present for some time. The facial weakness appears insidiously in the orbicularis oculi, zygomaticus, and orbicularis orbis muscles. The weakness generally progresses slowly and in a descending pattern from facial muscles to shoulder girdle to upper arms and then pelvic girdle muscles ( ,Fig, 36-.6,). There may be plateaus and even occasional arrest of the disorder.

Emery recommends that four criteria be present for the diagnosis of FSH MD: (1) onset in facial and shoulder muscles, with sparing of extraocular, pharyngeal, lingual, and cardiac muscles, (2) autosomal dominant inheritance pattern, (3) facial weakness in half or more of affected family members, and (4) myopathic changes, including polyphasic motor units of low amplitude and short duration on EMG and variation in fiber diameter, centrally located nuclei, and moth-eaten fibers on muscle biopsy. The unevenness of the disease process may extend to individual muscles. y

Several other problems have been identified in FSH MD, particularly in patients with early onset and relatively rapid progression. Hearing loss in the 4000 to 6000 Hz range and retinal capillary abnormalities (Coat's disease) have been reported. Although it is not usually clinically apparent, abnormal AV node or intranodal conduction also occur.y

There is no definitive treatment for FSH MD. Steroids may provide transient benefit if there are inflammatory changes on the muscle biopsy. Physical and occupational therapy are useful for maintaining optimal functioning. Orthotics and bracing may be helpful, as may surgical stabilization of the scapulae. Early photocoagulation of retinal abnormalities is recommended. y Large families who have been linked to the chromosome 4 locus may have their diagnosis verified by genetic testing. The course is relatively benign; most patients remain ambulatory, and lifespan is not significantly decreased. y

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