Useful investigations in a refractory case of 'myositis'.

The diagnosis of polymyositis is made on the basis of clinical features, muscle enzymes, EMG studies and muscle biopsy. Treatment requires corticosteroids often in combination with immunosuppressive agents, and relapse in spite of treatment may render management difficult. The case described below appeared to demonstrate features from which the diagnosis could be made, but in which the almost complete resistance to conventional therapy led to a correct reappraisal of the diagnosis. This illustrates an unusual cause for diagnostic confusion and the value of diagnosis reassessment under such circumstances.