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Clinical DescriptionSpinal and bulbar muscular atrophy (or Kennedy disease, named for the neurologist who originally recognized it) is a disorder of slowly progressive muscle weakness associated with mild androgen insensitivity [Kennedy et al 1968, Harding et al 1982, Hausmanowa-Petrusewicz etal 1983]. Only males are affected. Neurologic symptoms typically begin between the ages of 20 and 50 years [Arbizu et al 1983]. Onset of neurologic symptoms does not occur in childhood or adolescence. Early signs are difficulty with walking and a tendency to fall. Some patients have muscle cramps, while others complain of an action tremor [Nagashima et al 1988, Stefanis et al1975]. Deep tendon reflexes are decreased.After one to two decades of symptoms, most patients have difficulty climbing stairs. Typically, about one-third of patients require a wheelchair after two decades have passed since their initial presentation. With time, atrophy of the proximal musculature becomes prominent. Some patients also experience degeneration of the dorsal root ganglia, leading to mild abnormalities in sensory function in the distal extremities [Nagashima et al 1988, Sobue et al1981]. Electrodiagnostic studies are consistent with a diffuse denervation atrophy, anterior horn cell loss, and sensory neuronopathy [Olney et al 1991, Ferrante and Wilbourn 1997]. Most patients eventually show involvement of the bulbar muscles and have difficulty with speech articulation and swallowing [Ringel et al 1978]. Severely affected patients (many of whom are non-ambulatory) are at risk for asphyxiation or aspiration pneumonia because of weakness of the bulbar musculature [Kennedy et al 1968, Stefanis et al 1975]. This complication is the only life-threatening problem in SBMA, and probably only becomes important for about 10% of elderly males. Therefore, the vast majority of patients with SBMA have a normal life expectancy and do not die from direct complications of their motor neuron disease.
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