Patient 1 was a 30-yr-old woman complaining of progressive limb muscle weakness. She was in good health until age 12 yr, at which time she began to have a difficulty in raising her right arm above her head. Later, she developed increasing difficulties climbing stairs. By report, her mother had similar symptoms from the age of 40. His 35-yr-old brother was not affected clinically (). The neurological examination was remarkable for moderate facial weakness; moderate (Medical Research Council [MRC] grade 3) and mild (MRC grade 4) weakness of proximal upper and lower limb muscles, respectively; humeral atrophy; anterior axillary folds; winged scapulae; waddling gait; and hypoactive deep tendon reflexes. The serum creatine kinase (CK) was 233 IU/L (normal, <270 IU/L). Other routine laboratory tests including thyroid and parathyroid function were normal. Audiogram, electrocardiogram, echocardiogram, nerve conduction studies were unremarkable. Needle electromyography showed chronic myopathic changes in the left deltoid, biceps brachii, and vastus lateralis muscles. A muscle biopsy from the right vastus lateralis revealed marked fiber size variations, increased internalized nuclei, endomyseal fibrosis and fat ingrowth, and frequent lobulated myofibers.
Patient 3 was an 18-yr-old man complaining of progressive right upper limb weakness over the prior 3 yr. The initial diagnosis was idiopathic right brachial plexopathy. He was a tennis player in his early teens. There was no family history of neuromuscular disease (). Clinical examination of his parents was normal. Remarkable neurological findings included mild bifacial weakness; mild (MRC grade 4) and minimal weakness of the right and left proximal upper limb muscles, respectively; winged scapulae in the right side; and hypoactive deep tendon reflexes. The serum CK was 750 IU/L. Other routine laboratory tests including thyroid function were normal. Audiogram, electrocardiogram, echocardiogram, and nerve conduction studies were unremarkable. The FVC was 4.2 L (98% of predicted). Needle electromyography revealed chronic myopathic changes.