P043 Challenges in the diagnosis and management of immune-mediated necrotizing myopathy in a patient on long-term statins

Abstract

Abstract Background/Aims Statins are very common medications prescribed for cardiovascular disease prevention and with their ever-increasing use; we expect a significant increase in even the rarest side-effects. Immune-mediated necrotising myopathy (IMNM) is a rare type of autoimmune myopathy characterised by relatively severe proximal weakness and is most associated with the development of anti-HMGCoAR (3-hydroxy-3-methylglutaryl CoA Reductase) autoantibodies in statin users. The objective of this clinical case report is to highlight this rare condition to avoid incorrect diagnosis, particularly in primary care, to ensure prompt and specific management. Methods A 51-year-old female presented to her GP with gradual onset muscle weakness particularly around her shoulders and legs. She had a history of hypercholesterolemia, for which she had been on atorvastatin 20mg daily for 4 years. Results Following a blood test by her GP, a raised CK of 16,670 iU/L prompted a hospital admission due to suspected skeletal muscle damage. MRI scan of thighs showed features of myositis and muscle biopsy showed necrotic regenerating muscle fibres with lymphohistiocytic inflammation consistent with necrotizing myopathy. Blood tests revealed positive anti-HMGCoAR antibodies (negative ANA, DNA, ENA & other myositis-specific antibodies) confirming a diagnosis of anti-HMGCoAR IMNM. Atorvastatin was stopped and treatment was initiated with high-dose IV methylprednisolone followed by oral prednisolone tapering course. She showed only minor improvement in symptoms over the initial 6 weeks. Methotrexate was then added, with gradual improvement in her symptoms and normalization of CK over the next 6 months. Conclusion IMNM is unique in that it does not improve with statin discontinuation alone, and usually requires a combination of steroid and steroid-sparing immunosuppressant. Early diagnosis is crucial as commencing treatment early leads to better outcomes in patients. Anti-HMGCoAR antibodies are highly specific for this condition and not associated per se with hyperlipidaemia, self-limiting statin side effects or genetic muscle disease. In patients presenting with muscle weakness who are taking statins, it is beneficial to perform anti-HMGCoAR antibody test (especially if persistent symptoms despite statin cessation) to promptly differentiate this rare condition from more common but less severe statin related myotoxicities. Disclosure F. Khan: None. A. Kuttikat: None.