Anti-thyroid drugs-related myopathy: is carbimazole the real culprit?

Anti-thyroid drugs (ATDs)-related myopathy is rarely reported in literature, but once developed, it can cause significant morbidity to patient.

A 28-year old Chinese female was treated with carbimazole (CMZ) for Graves' disease with hyperthyroidism. Two weeks later, she developed myalgia and proximal muscle weakness. Investigations showed evidence of myopathy. CMZ was stopped and rapid improvement of clinical condition and biochemical parameters ensued.

Rapid decrement of thyroid hormone level is recognized as an important association for anti-thyroid drugs (ATDs)-related myopathy; however, the drug effects on muscle tissue cannot be excluded. Further elucidation of pathophysiology and identification of risk factors are needed. After commencing ATDs, early recognition of this rare condition and close monitoring are the essence of management. Different treatment strategies: dose reduction of ATDs, switching to alternative ATDs, with or without addition of thyroid hormone supplement can be applied depending on clinical situation.