Progressive proximal muscle weakness with subacute onset in an elderly patient: a case report

Statins are some of the most widely prescribed medications. Although statins are generally well tolerated, they can lead to musculoskeletal side effects. Statin-induced necrotizing autoimmune myositis (SINAM) is a rare condition and the prevalence is only 1 per 100,000 people. This disorder is characterized by progressive and severe symmetric muscle weakness, marked elevation of creatine kinase and persistent symptoms despite statin discontinuation. Electromyography commonly shows a nonspecific irritable myopathy pattern indistinguishable from other inflammatory myopathies. Muscle biopsy shows the presence of necrotic fibers, regenerating fibers without significant inflammatory cells and diffuse or focal upregulation of major histocompatibility complex class I expression. The anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (anti-HMGCR) antibodies represent a characteristic serological feature of SINAM.

We present a patient who developed progressive muscle weakness after taking simvastatin for the last seven years. At initial presentation, her creatine kinase level was 2,954 U/L and anti-HMGCR antibodies were positive. The biopsy showed a profound myopathic features with numerous necrotic fibers, some regenerating fibers and perimysial inflammatory cell infiltrate, combined with a diffuse overexpression of major histocompatibility complex class I products. She was diagnosed with SINAM, statin was suspended and a high dose of systemic corticosteroids, intravenous immunoglobulin therapy and methotrexate was started. At three-month follow-up, she had significant improvement in muscle strength and creatine kinase level returned to normal.

In this case, exclusion of inflammatory myopathies, metabolic muscle disorders and other neurological diseases is necessary for establishing a reliable diagnosis. In SINAM, simply discontinuing statin is often insufficient and aggressive immunosuppression or immunomodulation therapy is needed to achieve disease remission. This case aims to demonstrate that statins can induce serious muscular diseases that require aggressive immunosuppression.