Hypothyroidism presenting as a polymyositis-like syndrome. Report of two cases

Two patients with proximal muscle weakness and marked elevations of serum muscle enzymes were initially believed to have polymyositis; however electromyography and muscle biopsies were normal. Both patients were subsequently found to have hypothyroidism. Each regained her muscle strength, and serum enzymes normalized with thyroid hormone replacement. Because muscle weakness and an elevated creatine phosphokinase occur in most patients with hypothyroidism, thyroid dysfunction must be considered in the differential diagnosis of polymyositis.