Inclusion body myopathy

Inclusion body myopathy (IBM) is distinguished from polymyositis (PM) and dermatomyositis (DM) on the basis of clinical and histopathological features. A characteristic clinical phenotype is characterised by insidious onset of muscle weakness over months to years, muscle weakness localised predominantly in the thigh muscles and finger flexors, and resistance to glucocorticoid treatment. Typical histopathologic features include sarcoplasmic and nuclear inclusions and rimmed vacuoles.