Unusual cause of weight loss in a patient with HIV–hepatitis C virus coinfection

Recombinant interferon α (IFN α), alone or in combination, is used extensively in the treatment of hepatitis C infection. IFN therapy is not free of side-effects and autoimmune thyroiditis is one of its rare side-effects. We present here a case of a patient with hepatitis C virus–human immunodeficiency virus coinfection on interferon therapy who presented with significant weight loss. He was found to have IFN-related autoimmune thyrotoxicosis and responded to antithyroid drugs and propanolol. Therefore, this case highlights that IFN-induced thyroiditis is an unusual side-effect and that during treatment, a thyroid-stimulating hormone assay should be performed at regular intervals (every 8–12 weeks).