Cognitive deficits and cortical volume loss in COVID‐19‐related hyposmia

Abstract Background and purpose Studies have found that up to 73% of COVID‐19 patients experience hyposmia. It is unclear if the loss of smell in COVID‐19 is due to damage to the peripheral or central mechanisms. This study aimed to explore the impacts of COVID‐19‐induced hyposmia on brain structure and cognitive functions. Methods The study included 36 hyposmic (h‐COV) and 21 normosmic (n‐COV) participants who had recovered from mild COVID‐19 infection, as well as 25 healthy controls (HCs). All participants underwent neurological examination, neuropsychiatric assessment and Sniffin’ Sticks tests. High‐resolution anatomical images were collected; olfactory bulb (OB) volume and cortical thickness were measured. Results Addenbrooke's Cognitive Examination—Revised total and language sub‐scores were slightly but significantly lower in the h‐COV group compared to the HC group ( p = 0.04 and p = 0.037). The h‐COV group exhibited poorer performance in the Sniffin’ Sticks test terms of discrimination score, identification score and the composite score compared to the n‐COV and HC groups ( p < 0.001, p = 0.001 and p = 0.002 respectively). A decrease in left and right OB volumes was observed in the h‐COV group compared to the n‐COV and HC groups ( p = 0.003 and p = 0.006 respectively). The cortical thickness analysis revealed atrophy in the left lateral orbitofrontal cortex in the h‐COV group compared to HCs. A significant low positive correlation of varying degrees was detected between discrimination and identification scores and both OB and left orbital sulci. Conclusion Temporary or permanent hyposmia after COVID‐19 infection leads to atrophy in the OB and olfactory‐related cortical structures and subtle cognitive problems in the long term.