Recovery of olfactory function following URTI is frequent, even many years after the infectious insult. Upper respiratory tract infection is the commonest cause of olfactory loss. Many treatment options exist including topical steroids, vitamin B, acupuncture, and zinc, which can be used to treat olfactory loss, but no effective therapy is available to date except olfactory training. This article was a retrospective cohort study from two institutions in Germany and Sweden; looking at significant predictors for olfactory recovery in a large sample of patients with postinfectious olfactory loss (i.e. not due to head trauma/sinus disease/toxic exposure/congenital anosmia etc.) based on standardised objective testing methods (Sniffin Sticks test). The Sniffin Sticks tests three different olfactory functions: odour threshold (T), odour discrimination (D), and odour identification (I). Functional anosmia depends on the summative score of the three thresholds (TDI score). The principal factor identified as affecting the olfactory recovery was the initial TDI score – the higher the initial score, the higher probability of normosia. Age was another factor, with older people more vulnerable to poor recovery, presumably characterised by a decrease in the size of the olfactory epithelium and consequent loss of the number of olfactory receptor neurons. Finally, it was interestingly observed that the sooner patients attended the clinic after developing olfactory loss, the higher chance of exhibiting improvement (better TDI scores). This might indicate that there is a “window of recovery” within a specific time window. 

Postinfectious olfactory loss: a retrospective study on 791 patients.
Cavazzana A, Larsson M, Munch M, Hahner A, Hummel T.
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Gentle Wong

Guy's and St Thomas' Hospitals, UK.

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