Since its delineation in the early 1970s, it has become apparent that inclusion body myositis (IBM) is the most commonly-acquired myopathy in middle-aged and older people. Although classified as one of the inflammatory myopathies, with polymyositis and dermatomyositis, several features set it apart, not least its resistance to immunosuppressant therapies. The diagnosis may be strongly suspected on the basis of clinical features alone, but confirmation is by the demonstration, in a muscle biopsy specimen, of characteristic light and electron microscopic changes
Most cases present after the age of 50 years. IBM is substantially commoner in men, by at least 5 : 1. The overall incidence is in the order of 1/100 000 population/annum.
Patients typically present with symptoms relating to quadriceps weakness (Figs 1–3): ‘knees giving-way’, difficulty in rising from a chair and squatting. Observers may comment on quadriceps atrophy. It is the most common cause