COVID-19 Anosmia Study

Infection with the novel coronavirus (COVID-19) has been linked to new-onset olfactory dysfunction, often as the only presenting symptom. In one multicenter European study, 85.6% of patients with mild to moderate symptoms reported hyposmia or anosmia with early recovery of olfactory function in just under half of patients. However, the pathogenesis and natural history of COVID-19 related olfactory dysfunction is poorly understood.

Anosmia most commonly arises in association with sinonasal disease or post-infectious or post-traumatic disorders. Notably, olfactory loss has been associated with impaired quality of life, higher rates of depression, and even increased mortality risk. Spontaneous recovery has been observed in patients with post- infectious olfactory dysfunction, typically over a period of months to years, with an estimated one-third of patients demonstrating meaningful improvement after one year.

Smell retraining therapy appears to be an effective therapeutic option for patients with post-infectious olfactory dysfunction, particularly for patients who initiate treatment within one year from onset of symptoms, but requires an intervention period of at least three to four months. Various pharmacotherapies have been investigated in the treatment of post-infectious anosmia but none have clearly demonstrated utility with the exception of a possible benefit for nasal steroid irrigations in combination with smell retraining therapy.

More recently, omega-3 polyunsaturated fat supplementation has emerged as a promising pharmacotherapy for olfactory dysfunction in patients without sinonasal disease. Omega-3 fatty acid deficient mice demonstrate evidence of olfactory dysfunction and mice receiving omega-3 fatty acids have improved recovery after peripheral nerve injury, which has been linked to neuroprotective effects mediated through anti-oxidant and anti-inflammatory pathways. In humans, a large cross-sectional study found that older adults with higher dietary fat intake had lower incidence of olfactory impairment. From a clinical perspective, patients without sinonasal disease receiving postoperative omega-3 fatty acid supplementation after endoscopic endonasal skull base surgery in a randomized control trial demonstrated a significantly greater rate of return of normal olfactory dysfunction.

Little is known about either the natural history of olfactory dysfunction associated with COVID-19 infection or about the therapeutic efficacy of omega-3 fatty acid supplementation in patients with post-viral anosmia. The study team hopes to gain a better understanding of each through a randomized double-blind placebo control study that assesses both objective and subjective perception of olfactory dysfunction over a period of 6 weeks after infection.