Inclusion body myositis (IBM): myopathy or neuropathy?

Inclusion body myositis (IBM) is described in six elderly patients (three women) and in a young familial patient. They all showed the morphologically characteristic vacuoles containing osmiophilic membranous whorls and intracytoplasmic or intranuclear inclusions. There is a well-delineated bimodal age spectrum of IBM, with onset in the second and sixth decades, but otherwise the disorder seems to be a specific entity. Clinical, electrophysiologic, and morphologic features suggest a neurogenic origin in some cases.