Permanent Anosmia in a Patient Treated with Pegylated Interferon Alfa

Abstract

Introduction: Interferon Alfa has antiviral and antiproliferative immunomodulatory effects. It is known to cause diabetes, hypothyroidism and certain dermatologic conditions. There have been 6 case reports demonstrating temporary anosmia due to use of this drug and one case report showing permanent anosmia. This is a case report of Interferon Alfa causing permanent anosmia. Case Report: A 57-year-old male with known hepatitis C infection was treated with Pegylated Interferon Alfa (IFN- alfa). Patient developed anosmia and cacosmia within few weeks of starting treatment. He was however continued on the medication to treat hepatitis C for 48 weeks but failed treatment. Interferon Alfa was discontinued but patient continued to have anosmia even 12 months after completing treatment. There was no history of recurrent allergies or sinusitis. Neurology had evaluated the patient and there was no cranial nerve abnormality. MRI of the brain ruled out any organic cause. He did not show any signs of Alzheimer's dementia or Parkinson's disease. He was extensively evaluated by ENT (otorhinolaryngiologist) as well. He had no evidence of nasal obstruction, polyps, mass, fractures, infection or atrophy of mucosa. His anosmia was thought to be permanent due to use of Pegylated Interferon Alfa. Discussion: Anosmia is a rare side effect of IFN-alfa and can develop with 2 weeks of starting treatment. It has been known to persist up to 13 months after discontinuing the medication. The exact mechanism of action by which this medication causes anosmia is not well understood. It is proposed that it is due to changes in neuroendocrine hormonal effects due to immunoregulatory effects of IFN-alfa. Alternatively, it may stimulate autoantibodies which can destroy the myelin sheath of peripheral nerves and cause permanent nerve damage. It is important to know this rare side effects of IFN-alfa so that patients may be informed about it. It will be unethical to start this medication without informing patients about this side effect especially if it can cause permanent anosmia since there is a chance that he may fail treatment as well.Table: Drugs causing anosmia