A 53-year-old woman had development of subacute-onset muscle weakness resulting in difficulty climbing stairs, rising from a chair, and reaching over her shoulders. She reported no dysphagia, dysarthria, dyspnea, or diplopia. She also disclosed no rash, joint pain, or urine discoloration. She had no history of statin exposure. There was no family history of neuromuscular disorders, early cataracts, cardiac arrhythmia, or cardiomyopathy. Two months of treatment with prednisone had resulted in no clinical improvement. Neurologic examination indicated moderate neck flexor, shoulder, and hip girdle muscle weakness, with sparing of cranial muscles. There was no action- or percussion-induced myotonia. Needle electromyography showed short-duration, low-amplitude, and complex motor unit potentials, predominantly affecting proximal muscles, associated with fibrillation potentials and myotonic discharges in proximal and axial muscles. Her creatine kinase level was increased. Biopsy of the left quadriceps showed variation in muscle fiber size, a moderate increase in internalized nuclei, fiber splitting, and scattered necrotic and regenerating fibers. There was a mild increase in perimysial fibrous and fatty connective tissue. 3-Hydroxy-3-methylglutaryl–coenzyme A reductase antibodies were strongly positive. The patient was diagnosed with hydroxy-3-methylglutaryl–coenzyme A reductase antibody–positive necrotizing autoimmune myopathy. The patient received intravenous immunoglobulin and mycophenolate mofetil while continuing prednisone. At 1-year follow-up, she had no weakness, and her creatine kinase value was normal while she continued taking prednisone, mycophenolate mofetil, and intravenous immunoglobulin. Necrotizing autoimmune myopathy, or immune-mediated necrotizing myopathy, is a subtype of immune-mediated myopathy, clinically characterized by subacute, progressive, proximal limb weakness and persistently increased creatine kinase level. Pathologically, it is characterized by myonecrosis with minimal or no inflammation. One-third of patients with necrotizing autoimmune myopathy have myalgia.
Paraneoplastic Necrotizing Autoimmune Myopathy in a Patient Undergoing Laparoscopic Pancreatoduodenectomy for Distal Cholangiocarcinoma
