[Muscle weakness and CK elevation: is it myositis?]

Rheumatologists are often confronted by patients with muscle weakness and elevated creatine kinase (CK) levels. Myositis cannot always be determined to be the cause of the complaints. This article presents two cases from our hospital where the diagnosis could only be determined by muscle biopsy. In the first case the patient presented with muscle weakness, pathological weight loss and a significant increase in CK levels. A muscle biopsy revealed an immune-mediated necrotizing myopathy (IMNM) caused by anti-3-hydroxy-3-methyl-gulatryl-CoA reductase (HMG-CoA reductase) autoantibodies due to the intake of statins. The second patient presented with cramp-like and burning muscle pain and weakness of the extremities without a relevant increase in CK level. Myoadenylate deaminase deficiency was also detected by muscle biopsy, and further confirmed by genetic testing.