Anti-Thyroid Drugs-Related Myopathy: Is Carbimazole the Real Culprit?

Abstract

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

Potential Effect of Carbimazole on Parotid Acini of Albino Rats

“…The present study aimed to discover the possible effect of carbimazole on parotid gland acini, since carbimazole is the most commonly used anti-thyroid drug (12).…”

Cross-sectional investigation of serum creatine kinase concentration in Graves disease patients treated with oral antithyroid drugs

“…Previous research has found that oral ATDs related myopathy was mostly involved MMI and carbimazole, [ 15 , 16 ] PTU has also been reported. Carbimazole is rarely used in China.…”

Myopathy in hyperthyroidism as a consequence of rapid reduction of thyroid hormone

“…Myopathy onset during treatment for hyperthyroidism with ATDs was once considered simply as a rare adverse effect of ATDs. [ 13 – 16 , 21 ] However, relative hypothyroidism was not carefully excluded in any of these cases. In one recent case attributing myopathy to the effect of carbimazole, [ 21 ] the reported patient presented with a FT4 level lower than the normal range at the time when muscular symptoms onset, suggesting an evident hypothyroid state.…”

“…[ 13 – 16 , 21 ] However, relative hypothyroidism was not carefully excluded in any of these cases. In one recent case attributing myopathy to the effect of carbimazole, [ 21 ] the reported patient presented with a FT4 level lower than the normal range at the time when muscular symptoms onset, suggesting an evident hypothyroid state. In another case attributing myopathy to MMI, [ 16 ] the reported patient presented with borderline FT4 levels at the lower limit during the 2 weeks when CK level elevated to between 651 and 3775 U/L.…”