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

Area of Science:

• Neurology
• Rheumatology
• Genetics

Background:

• Rheumatologists frequently encounter patients with muscle weakness and elevated creatine kinase (CK) levels.
• Diagnosing the specific cause of myopathy can be challenging, as myositis is not always the underlying condition.
• Muscle biopsy is an essential diagnostic tool when initial evaluations are inconclusive.

Observation:

• Case 1: A patient presented with severe muscle weakness, pathological weight loss, and significantly elevated CK levels.
• Case 2: Another patient experienced cramp-like and burning muscle pain with limb weakness, but without markedly increased CK levels.

Findings:

• Muscle biopsy in Case 1 revealed immune-mediated necrotizing myopathy (IMNM) associated with anti-3-hydroxy-3-methyl-glutaryl-CoA reductase (HMG-CoA reductase) autoantibodies, likely induced by statin use.
• Muscle biopsy in Case 2 identified myoadenylate deaminase deficiency, a diagnosis further confirmed by genetic testing.

Implications:

• These cases underscore the diagnostic utility of muscle biopsy in identifying specific myopathies, including statin-induced IMNM and myoadenylate deaminase deficiency.
• The findings emphasize that elevated CK levels are not always present in all myopathies, necessitating alternative diagnostic approaches.
• Accurate diagnosis through muscle biopsy and genetic testing is critical for appropriate patient management and treatment strategies in rheumatology and neurology.