Reduced Olfactory Bulb Volume Accompanies Smelling Dysfunction After Mild SARS-CoV-2 Infection: The Hamburg City Health Study COVID Program (preprint)

ABSTRACT

BackgroundDespite its high prevalence, the determinants of smelling impairment in COVID-19 remain opaque. Olfactory bulb volumetry has been previously established as a promising surrogate marker of smelling function in multiple otorhinolaryngological diseases. In this work, we aimed to elucidate the correspondence between olfactory bulb volume and the clinical trajectory of COVID-19-related smelling impairment. Therefore, we conducted a large-scale magnetic resonance imaging (MRI)-based investigation of individuals recovered from mainly mild to moderate COVID-19. MethodsData of 233 COVID-19 convalescents from the Hamburg City Health Study COVID Program were analyzed. Upon recruitment, patients underwent cranial MR imaging and assessment of neuropsychological testing. Automated olfactory bulb volumetry was performed on T2-weighted MR imaging data. Olfactory function was assessed longitudinally after recruitment and at follow-up via a structured questionnaire. Follow-up assessment included quantitative olfactometric testing with Sniffin Sticks. Group comparisons of olfactory bulb volume and olfactometric scores were performed between individuals with and without smelling impairment. The associations of olfactory bulb volume and neuropsychological as well as olfactometric scores were assessed via multiple linear regression. ResultsLongitudinal assessment demonstrated a declining prevalence of olfactory dysfunction from 67.6% at acute infection, 21.0% at baseline examination (on average 8.31 {+/-} 2.77 months post infection) and 17.5% at follow-up (21.8 {+/-} 3.61 months post infection). Participants with post-acute olfactory dysfunction had a significantly lower olfactory bulb volume [mm3] at scan-time than normally smelling individuals (mean {+/-} SD, baseline 40.76 {+/-} 13.08 vs. 46.74 {+/-} 13.66, f=4.07, p=0.046; follow-up 40.45 {+/-} 12.59 vs. 46.55 {+/-} 13.76, f=4.50, p=0.036). Olfactory bulb volume successfully predicted olfactometric scores at follow-up (rsp = 0.154, p = 0.025). Performance in neuropsychological testing was not significantly associated with the olfactory bulb volume. ConclusionsOur work demonstrates the association of smelling dysfunction and olfactory bulb integrity in a sample of individuals recovered from mainly mild to moderate COVID-19. Olfactory bulb volume was demonstrably lower in individuals with sustained smelling impairment and predicted smelling function longitudinally. Collectively, our results highlight olfactory bulb volume as a surrogate marker that may inform diagnosis and guide rehabilitation strategies in COVID-19.