Polymyositis caused by a new genus of nematode.

We report two patients who presented with increasing malaise and myalgia, and had biopsy-proven polymyositis. Their conditions deteriorated after corticosteroid treatment, and repeat muscle biopsies showed adult and larval nematodes. Anthelminthic treatment was completely successful in both cases. The infecting nematode appears to belong to a new genus and is, to our knowledge, the first known muspiceoid nematode to infect humans. Its life cycle and the route of infection are unknown.