Carbimazole-Induced Hypothyroidism Presenting With Convulsions: A Therapeutic Paradox

Background: Carbimazole is widely used in the treatment of hyperthyroidism. Although effective, excessive suppression of thyroid hormone synthesis may result in iatrogenic hypothyroidism. Neurological manifestations such as seizures are uncommon and may complicate diagnosis. Case Presentation: A 53-year-old male with a history of hyperthyroidism on carbimazole therapy for six months presented with syncope and generalized tonic-clonic seizures. Laboratory evaluation revealed elevated thyroid-stimulating hormone (TSH) levels (37.483 µIU/mL) with decreased free T3 and free T4 levels, confirming hypothyroidism. Autoimmune markers including anti-thyroid peroxidase and TSH receptor antibodies were positive. Carbimazole-induced hypothyroidism was diagnosed. The drug was discontinued and levothyroxine therapy was initiated, resulting in clinical improvement. Conclusion: This case highlights the importance of regular monitoring of thyroid function during antithyroid therapy. Drug-induced hypothyroidism may present with atypical neurological features, leading to diagnostic challenges.