[A 81-year old man of anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase antibody-positive myopathy associated with lung adenocarcinoma cancer].

An 81-year-old man, who had no history of taking statins, developed progressive muscle weakness of the limbs and dysphagia. Laboratory tests showed a high level of CK and positivity for serum 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibodies. Tests for other autoantibodies to ARS and SRP were negative. A pathological analysis of the left biceps muscle revealed numerous necrotic and regenerated fibers with macrophage infiltration and deposition of C5b-9 complement in and around the myofibers. Chest CT showed a nodular shadow, which was suspected to be lung cancer, in the upper left lobe. A pathological analysis of a transbronchial lung biopsy specimen revealed lung adenocarcinoma with high level of HMGCR. He was diagnosed with HMGCR necrotizing myopathy associated with lung cancer, and both his muscle strength and dysphagia improved after three treatments with intravenous immunoglobulin (IVIg). He did not undergo surgery or radiation therapy because of interstitial pneumonia. This case suggests that a paraneoplastic mechanism caused the production of HMGCR antibodies, leading to myositis in this patient. Treatment with IVIg can be effective for patients with HMGCR antibody-positive paraneoplastic necrotizing myopathy that is refractory to corticosteroid therapy.