Spinal Muscular Atrophy (SMA)
Case Study B
A 40-year-old male first noted mild weakness in climbing stairs and running while in college. At presentation, he was ambulatory with a waddling gait. Examination demonstrated weakness of proximal muscles in the legs, pseudohypertrophy of the calves, and absent deep tendon reflexes in the legs. EMG demonstrated delayed recruitment and enlarged voluntary motor units, but no abnormal spontaneous activity. Nerve conduction studies were normal. Muscle biopsy revealed an increased variability of fiber calibers, some grouped atrophic fibers, and a predominance of fibers with type I histochemical features. A Spinal Muscular Atrophy (SMA) DNA test demonstrated absence of PCR product for both exons 7 and 8 of the Survival Motor Neuron (SMN) gene. A diagnosis of adult onset SMA was made.
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