Differential diagnosis between statin myotoxicity and inflammatory myositis – case presentation

Inflammatory myopathies, include polymyositis, dermatomyositis, inclusion body myositis and necrotising myopathy, but their diagnosis requires a comprehensive differential, in order to optimise treatment and to have the best outcome. One of the most controversial diagnosis in this situation is drug related myotoxicity, since the symptoms may vary significantly, but usually include muscle weakness and myalgia accompanied by elevated creatine kinase serum levels Patient background. We report a case of a 70 year-old patient, treated with statins, with onset of symptoms since one year with tolerable myalgia, accompanied by mild muscle weakness shortly after and progressive worsening in the last couple of months. Interruption of statins was recommended based on current symptoms and elevated muscle enzymes: creatine kinase (CK) x3 fold and aspartate aminotransferase (AST) x2 fold normal range. Investigations. Autoimmunity panel including anti-nuclear and 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibodies was negative. The needle EMG was abnormal, with diffuse fibrillation potentials in almost all investigated sites, both in the proximal and distal muscles. Complex repetitive discharges were also observed in most muscles tested. Existence of clear myogenic signs on needle EMG revealed the probable cause for the clinical presentation as being myogenic in nature. Discussion. Statin-induced myopathy (SIM) is typically self-limited showing remission in the following weeks or months after statin cessation. Although EMG studies support the presence of typical myopathy features in SIM, it cannot point-out specific changes attributed to a statin-related dysfunction. Patient outcome was favorable on hospital discharge. On a two week check-up, she reported improvement in muscle strength, range of motion and remitted myalgia. Repeated blood work showed a descending trend in both CK and AST, with values in normal range. Conclusions. The clinical case, the whole algorithm of clinical evaluation and paraclinical tests that lead to final diagnosis and the literature review, highlight the importance of an exhaustive approach. Electrophysiology tests offer important aid to the physician in the approach of patients with an underlying toxic myopathy in initial diagnosis, follow-up and biopsy yield if necessary.