Nearly all people with COVID-19 who lost their sense of smell gained it back, a small year-long study showed.
In a group of 51 patients who developed COVID-related anosmia in 2020, 96% had recovered by 12 months, reported Marion Renaud, MD, of University Hospitals of Strasbourg in France, and co-authors.
“Persistent COVID-19-related anosmia has an excellent prognosis with nearly complete recovery at 1 year,” the researchers wrote in a JAMA Network Open research letter. “As clinicians manage an increasing number of people with post-COVID syndrome, data on long-term outcomes are needed for informed prognostication and counseling.”
In April 2020, Renaud and colleagues published a single-center study of 97 adult outpatients with polymerase chain reaction (PCR)-confirmed COVID-19 and acute smell loss that lasted more than 7 days. Of this group, 51 people had subjective and objective assessments; 46 had subjective assessments only.
Subjective assessments included an online survey, which participants completed at 4-month intervals over the course of a year. Objective olfactory function was assessed by psychophysical testing using the Sniffin’ Sticks test. Participants were followed until objective olfactory recovery, with normal results defined as being at or above the 10th percentile.
Of the 51 participants who had subjective and objective assessments, 72.5% were women. The average baseline age of the group was about 38.
At 4 months, 23 of 51 patients (45.1%) reported full recovery of olfaction, 27 of 51 patients (52.9%) reported partial recovery, and one of 51 patients (2.0%) reported no recovery on subjective assessment. On psychophysical testing, 43 of 51 patients (84.3%) were objectively normosmic, including 19 of 27 who self-evaluated as only partially recovered. All patients who self-reported normal return of smell were corroborated with objective testing.
The remaining eight patients with persistent subjective or objective loss of smell were followed up at 8 months; an additional six patients became normosmic on objective testing. At 8 months, objective olfactory assessment confirmed full recovery in 49 of 51 patients (96.1%). Two people remained hyposmic at 1 year: one with abnormal olfactory threshold and one with parosmia causing abnormal identification.
Of participants who had subjective assessments only, 13 of 46 patients (28.2%) reported satisfactory recovery at 4 months (seven with total and six with partial recovery). The remaining 33 patients did so by 12 months (32 with total and 14 with partial recovery).
Other researchers have reported that 85.9% of mild COVID patients recovered olfaction at 6 months, but the findings of the current study suggest additional recovery can occur beyond a 4- or 6-month window, Renaud and co-authors observed. “This supports findings from fundamental animal research, involving both imaging studies and postmortem pathology, suggesting that COVID-19-related anosmia is likely due to peripheral inflammation,” they wrote.
The study also confirmed that discrepancies persist between self-assessed and objective testing and some people aren’t aware when normal function returns.
“This highlights the importance of applying both methods for postviral olfactory disorder evaluation,” the researchers pointed out. “Discrepancies could be explained by qualitative disorders disrupting self-assessment (e.g., parosmia) and/or limited capacity of olfactory tests to capture a complete return to function among individuals with higher baseline olfactory abilities.”
The study’s main limitation is that only 51 people had objective olfactory testing. The group also consisted primarily of women under 50; both female sex and younger age are positively associated with full olfaction recovery.
This work was supported by French state funds managed within the Plan Investissements d’Avenir and by the Agence Nationale de la Recherche.
The researchers reported no conflicts of interest.