Interventions for the treatment of persistent post‐COVID‐19 olfactory dysfunction

Background Olfactory dysfunction is an early and sensitive marker of COVID‐19 infection. Although self‐limiting in the majority of cases, when hyposmia or anosmia persists it can have a profound effect on quality of life. Little guidance exists on the treatment of post‐COVID‐19 olfactory dysfunction, however several strategies have been proposed from the evidence relating to the treatment of post‐viral anosmia (such as medication or olfactory training). Objectives To assess the effects (benefits and harms) of interventions that have been used, or proposed, to treat persisting olfactory dysfunction due to COVID‐19 infection. A secondary objective is to keep the evidence up‐to‐date, using a living systematic review approach. Search methods The Cochrane ENT Information Specialist searched the Cochrane COVID‐19 Study Register; Cochrane ENT Register; CENTRAL; Ovid MEDLINE; Ovid Embase; Web of Science; ClinicalTrials.gov; ICTRP and additional sources for published and unpublished studies. The date of the search was 16 December 2020. Selection criteria Randomised controlled trials including participants who had symptoms of olfactory disturbance following COVID‐19 infection. Only individuals who had symptoms for at least four weeks were included in this review. Studies compared any intervention with no treatment or placebo. Data collection and analysis We used standard Cochrane methodological procedures. Primary outcomes were the recovery of sense of smell, disease‐related quality of life and serious adverse effects. Secondary outcomes were the change in sense of smell, general quality of life, prevalence of parosmia and other adverse effects (including nosebleeds/bloody discharge). We used GRADE to assess the certainty of the evidence for each outcome. Main results We included one study with 18 participants, which compared the use of a 15‐day course of oral steroids combined with nasal irrigation (consisting of an intranasal steroid/mucolytic/decongestant solution) with no intervention. Psychophysical testing was used to assess olfactory function at baseline, 20 and 40 days. Systemic corticosteroids plus intranasal steroid/mucolytic/decongestant compared to no intervention Recovery of sense of smell was assessed after 40 days (25 days after cessation of treatment) using the Connecticut Chemosensory Clinical Research Center (CCCRC) score. This tool has a range of 0 to 100, and a score of ≥ 90 represents normal olfactory function. The evidence is very uncertain ab