Statin-Associated Immune-Mediated Necrotizing Myopathy: Presentation in an Atypical Age Group

Abstract

BACKGROUNDImmune-mediated necrotizing myopathy (IMNM) is a subgroup of systemic autoimmune myopathies characterized histologically by the presence of necrotic muscle fibers and the absence or minimal presence of inflammatory cell infiltrate. Clinically, it is characterized by significant proximal muscle weakness. Laboratory examination shows a significant elevation of serum muscle enzymes, in addition to the presence of anti-signal recognition particle (SRP) or anti-3-hydroxy-3-methyl-glutaryl-coenzyme A reductactase (HMGCR) autoantibodies. IMNM affects mainly adults, women, with a peak between 40 and 50 years. IMNM results from the interaction of environmental factors in genetically predisposed individuals. In the form associated with the anti-HMGCR autoantibody, the HMGCR enzyme is exposed to the cell membrane, functioning as an antigen. HMGCR exposure is most often triggered by exposure to statins. We will report a case of IMNM in an elderly patient, with previous exposure to statin. CASE REPORTFemale, 70 years old, white, with a history of systemic arterial hypertension, dyslipidemia, type 2 diabetes, hypothyroidism and osteoporosis. In use of venlafaxine, AAS, zolpidem and dexlansoprazole. She was hospitalized with a history of generalized weakness, diffuse myalgia, profuse sweating, dysphagia, and weight loss of 10 kg, beginning 4 months prior to admission. On clinical examination, the patient presented grade II muscle strength assessment-Manual Muscle Testing (MMT-8). Laboratory evaluation showed a significant increase in muscle enzyme (creatine phosphokinase: 9,000 U/L). The search for autoantibodies was negative, except for the positivity of anti-HMGCR. Investigation for neoplasia was also negative. Muscle biopsy showed moderate to severe myopathy, with the impression of chronic polymyositis probably associated with a statin. The patient reported previous use of simvastatin for 3 years, being suspended at the beginning of the condition, when muscle weakness started. She received pulse therapy with 1 g of methylprednisolone, 3 days in a row, and opted for the use of oral methotrexate and intravenous human immunoglobulin, applied monthly, for 5 months, in addition to a gradual reduction in corticosteroids. She evolved with clinical and laboratory improvement. CONCLUSIONStatin-induced necrotizing myopathy is a rare condition with a challenging, sometimes time-consuming diagnosis, depending on the availability of specific tests. However, when recognized in time, there is effective treatment with good clinical response. It is important to consider the diagnosis in the face of myopathy with marked elevation of muscle enzymes, regardless of age, in patients exposed to statins.