Endocrine Abstracts

Introduction: There are many causes of rhabdomyolysis, with Carbimazole, the first line treatment for hyperthyroidism, being one of the rarest. Rhabdomyolysis can potentially cause significant morbidity and mortality if left untreated.

Case: A 38 year old female presented to the Emergency Department in May 2018 with a 4 day history of severe sudden onset bilateral thigh pain. Her only prior health problem was primary hyperthyroidism for which she had been receiving Carbimazole therapy (started December 2017). At diagnosis, Thyroid Stimulating Hormone (TSH) was 0.05 mU/l and T4 46.4 pmol/l. On admission, her Creatinine Kinase (CK) was found to be 32721 U/l. Common causes of rhabdomyolysis were excluded including: bacterial and viral infection, autoimmune, heatstroke, alcohol excess and trauma. Her CK gradually decreased after stopping Carbimazole and receiving intravenous fluids. She stayed in hospital for 8 days and was discharged with a CK of 383 U/l. Prior to discharge Propylthiouracil therapy was commenced as her thyroid function tests worsened (TSH <0.05 mU/l, T4 20.0 pmol/l) from being euthyroid. This was used as a bridging therapy prior to definitive surgical cure. Whilst on Propylthiouracil her CK remained low.

Discussion: Rhabdomyolysis secondary to anti-thyroid drugs (including Propylthiouracil) appears to be relatively rare, though the specific incidences have not been researched. The mechanism of Carbimazole induced Rhabdomyolysis is not fully understood. Other case reports have suggested that rapid improvement of hyperthyroidism may be a contributing factor. However, our case goes against this theory as the patient had been on Carbimazole for over 6 months and was still thyrotoxic when diagnosed with rhabdomyolysis.

Conclusion: Although not yet fully understood, this rare cause of rhabdomyolysis is important for clinicians to be aware of because of its simple yet effective management of stopping the medication.