Olfactory mucosal histopathologic changes in persistently anosmic patients Post COVID-19 Infection – A case-series study

Olfactory dysfunction (OD)—including anosmia, hyposmia, and parosmia—is a prevalent symptom of COVID-19. Despite its high incidence, the pathophysiology and duration of OD remain unclear. Aim: To investigate histopathologic changes in the olfactory mucosa of patients with persistent post–COVID-19 anosmia. Methods: We conducted a case-series of 32 PCR-verified COVID-19 patients with persistent anosmia (>3 months) from March 1, 2023, to March 1, 2024. Endoscopically guided biopsies of the olfactory epithelium were processed and examined histopathologically. Results: Extensive loss of surface epithelium occurred in 81.3% (n = 26), nearly normal epithelium in 18.8% (n = 6), and lamina propria was preserved in 100.0% (n = 32). Chronic inflammation was present in all cases and was severe in 75.0% (n = 24). The recovery of anosmia had a significant inverse relation to the severity of inflammation, and patients with less mucosal damage and younger age had a better chance of rapid improvement. Conclusions: Our findings suggest that damage to the olfactory epithelium and inflammatory infiltration are key contributors to post-COVID-19 anosmia. The duration of anosmia recovery is associated with the degree of mucosal damage, inflammation, and patient age. These results provide valuable insights into the underlying mechanisms of OD and may inform the development of targeted therapeutic strategies.