Endocrine Abstracts

Case: In April 2008, a 68-year-old male was referred to the endocrine clinic with symptoms of hyperthyroidism and was prescribed carbimazole 20 mg daily. A week later, he developed sudden onset dizziness, together with reduced hearing in his left ear and associated tinnitus. Similar symptoms developed in his right ear shortly thereafter. Seven weeks after starting carbimazole, he attended the ENT outpatient clinic with severe vertigo, tinnitus and bilateral hearing loss. Otoscopy revealed normal tympanic membranes and middle ears bilaterally. Pure tone audiometry revealed moderate to severe bilateral asymmetrical sensorineural hearing loss. Carbimazole was felt likely to be a factor in the development of his symptoms, and was therefore changed to propylthiouracil 200 mg daily. On review two weeks later he felt his dizziness was improved though he remained unsteady on his feet. His profound deafness and bilateral tinnitus continued. His autoimmune screen was normal, except for a positive ENA and LNA with rho pattern. Following endocrine review his propylthiouracil was withdrawn, in case this was also implicated in his symptomatology. His hyperthyroidism recurred soon after, and he underwent total thyroidectomy with potassium iodide cover. On subsequent ENT review, his dizziness had improved though his tinnitus persisted. His hearing continued to deteriorate particularly in the low tones of the right ear.

Discussion: Acute ototoxicity is a rare but important complication of thiourea derived antithyroid drugs. Although previous cases have been reported in the medical literature, these cases occurred in younger with serological evidence of lupus like syndrome with positive anti ds DNA antibodies and ANCA. The management options include stopping the culprit drug and treatment with immunosuppressive drugs or referring the patient for urgent thyroidectomy. Healthcare professionals who prescribe antithyroid drugs should be aware of this rare but potentially serious complication, so that early drug withdrawal, and referral for surgery can be considered.