Trismus. An unusual sign in polymyositis.

Neuromuscular disease is an unusual cause of trismus. However, we describe two patients with severe polymyositis who had difficulty opening their mouths during the acute phase of the illness. Electromyography demonstrated involvement of the masseters, and there was no evidence of myasthenia. The mechanism appeared to be decreased elasticity of the masseter because of inflammation, edema, and perhaps contractures.