A new French study, however, includes some reassuring news: Smell returns in the overwhelming majority of patients within a year.
Researchers from University Hospitals in Strasbourg, France reached that conclusion about clinical course and prognosis by following a cohort of patients with COVID-19–related anosmia for 1 year and performing repeated olfactory function testing for a subset of patients. Their results were published in JAMA Network Open.
The same group of researchers published a study in April 2020 about a cohort of patients with polymerase chain reaction–proven COVID-19 with acute smell loss lasting more than 7 days. Over a year, at 4-month intervals, patients were asked to complete a survey and have their olfactory function assessed by psychophysical testing, including the threshold and identification tests, Sniffin’ Sticks Test and Burghardt.
Researchers continued to follow hyposmic or anosmic patients until objective olfactory recovery (normal results were defined as those at or above the 10th percentile. The authors performed data analysis from June 2020 to March 2021.
Overall, 97 patients—69.1% women with mean age of 38.8 years and acute smell loss—were evaluated. Of those, 52.6% underwent both subjective and objective olfactory tests, and 47.4% underwent subjective assessment alone.
Researchers report that, after subjective assessment at 4 months, 45.1% reported full recovery of olfaction, 52.9% reported partial recovery, and 2.0% reported no recovery. On psychophysical testing, 4.3% were objectively normosmic, including 70.0% who evaluated themselves as only partly recovered.
The remaining eight patients (15.7%) with persistent subjective or objective loss of smell were followed up at 8 months, and an additional six patients became normosmic on objective testing, according to researchers, who advise that, at 8 months, objective olfactory assessment confirmed full recovery in 49 of 51 patients (96.1%).
Still, two patients remained hyposmic at a year, with persistent abnormalities—one with abnormal olfactory threshold and one with parosmia causing abnormal identification. Researchers add that, among those who underwent subjective assessment alone, 28.2% reported satisfactory recovery at 4 months and the remaining 71.7% reached that point by 12 months.
“More than 1 year into the pandemic, we describe the long-term prognosis for a cohort of patients with COVID-19–related anosmia, most of whom (96.1%) objectively recovered by 12 months,” the authors write. “Our findings suggest that an additional 10% gain in recovery can be expected at 12 months, compared with studies with 6 months of follow-up that found only 85.9% of patients with recovery. 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.”
The study team also points out that their findings confirm the discrepancies between self-assessed and objective testing, noting that participants often fail to recognize the return of normosmia. “This highlights the importance of applying both methods for postviral olfactory disorder evaluation,” the authors add. “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 concludes, “Persistent COVID-19–related anosmia has an excellent prognosis with nearly complete recovery at one year. As clinicians manage an increasing number of people with post-COVID syndrome, data on long-term outcomes are needed for informed prognostication and counseling.”
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