Hoffman's syndrome: muscle stiffness, pseudohypertrophy and hypothyroidism.

Primary hypothyroidism is a chronic and insidious disease caused by failure of thyroid hormone production. We observed a 38-year-old woman admitted to our hospital due to progressive proximal weakness, muscle pain and fatigue during mild exercise. Laboratory tests showed features of rhabdomyolysis and hypothyroidism. After examination of the thyroid, we reached a diagnosis of Hashimoto's thyroiditis and hypothyroid myopathy. Hypothyroidism should be considered as a differential diagnosis of creatine kinase elevation; actually, neuromuscular symptoms and signs occur in most newly diagnosed patients with thyroid diseases. Hypothyroidism presenting as muscle stiffness and pseudohypertrophy is called 'Hoffman's syndrome'.