C42-51 A Case of Statin-induced Necrotizing Autoimmune Myopathy - Or Is It?

Abstract Introduction Statins are a commonly used medication which acts via inhibition of the enzyme 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR). Side effects include myalgias, elevated creatine kinase (CK), rhabdomyolysis and self-limited statin myopathy. It is also associated with a rare and potentially life-threatening autoimmune myopathy known as statin-induced necrotizing autoimmune myopathy (SINAM). Case 60-year-old male with a history of stage III non-small cell lung cancer treated with durvalumab therapy, hyperlipidemia (on atorvastatin 5 years) presented with worsening proximal bilateral lower extremity weakness without pain or sensory changes. Blood work showed CK of 6,457, CK-MB of 127 and CRP of 4.2. Electromyography was notable for electrical myotonia and signs of irritable myopathy. Initial myositis panel was significant for +MDA5 antibody, anti-HMG Coa Reductase, and subsequently TIF-1. Left thigh MRI showed inflammation of the anterior and lateral compartments. Anterior thigh muscle biopsy was significant for scattered myonecrosis of the skeletal muscle with abundant regenerating myofibers and mild inflammatory infiltrates. Given the high suspicion of statin-induced necrotizing myositis the patient was treated with a 3-day course of intravenous immunoglobulin (IVIG) and pulse dose solumedrol with gradual improvement in symptoms. He was discharged with oral prednisone taper and plan for monthly IVIG infusions. Discussion SINAM is a rare disease. Diagnosis is made using clinical, serologic, and histopathologic findings in a patient with a history of statin use. Detection of anti-HMGCR antibodies using enzyme-linked immunosorbent assay has a 90% sensitivity and specificity. Interestingly, in addition to a positive anti-HMGCR antibody, his myositis panel was significant for MDA5 and TIF-1. These are closely linked to dermatomyositis and rapidly progressive interstitial lung disease. Distinguishing between SINAM and dermatomyositis was pertinent as prognosis and management differ. Both SINAM and dermatomyositis present with proximal muscle weakness. Cutaneous findings (not seen in this case) will only be present in dermatomyositis. Muscle biopsy in dermatomyositis will show perifascicular atrophy and perivascular inflammation. This differs from the muscle biopsy in SINAM which will exhibit prominent necrosis and macrophage infiltration, with minimal lymphocytic involvement, like that seen in our patient. Both dermatomyositis and SINAM are treated with immunosuppressive medications including steroids and IVIG. However, additional management of dermatomyositis includes screening for underlying malignancy and assessment for rapidly progressive interstitial lung disease. Conversely, management of SINAM includes indefinite cessation of the offending statin. Overall, our patient’s presentation was most consistent with SINAM. He, reassuringly, had improvement in symptoms and clinical findings with treatment as above. This abstract is funded by: None