Olfactory training for patients with olfactory loss after upper respiratory tract infections

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Abstract
Olfactory training consisting of daily suprathreshold odor exposure over 12 weeks seems to improve olfactory function. It is unknown if a longer period of training might be more effective. A prospective non-randomized clinical study was performed including 39 patients with olfactory loss after an upper respiratory tract infection (URTI) of less than 24 months duration. Patients exposed themselves with suprathreshold concentrations of four odors (rose, eucalyptus, lemon, cloves) applied in ‘‘Sniffin’ Sticks’’ felt-tip pens over 32 weeks. Olfactory function was performed before (T1), after 16 weeks (T2), and 32 weeks of training (T3) using the ‘the Sniffin’ Sticks test kit calculating the TDI score (Threshold, Discrimination, Identification). The mean TDI score showed a non-significant trend of improvement at T2, and was significantly increased at T3 (p = 0.021). Overall, 31 patients (79 %) showed an increased TDI score at T3. The increase of TDI from T1 to T3 was 4.6 ± 5.1. Age, gender, duration and initial severity of olfactory loss had no influence on the improvement (all p > 0.05). Only patients with a D score lower than the median value of 8 showed a significantly higher increase of the D score at T3 (p = 0.004). The present study confirmed that olfactory training improves olfactory function in patients with olfactory loss after URTI. A longer duration of training over 32 weeks seems to increase the effectiveness in comparison to a 12-week period. This was tested in a completed German multicenter trial to be published soon containing a control group to include the effect of a spontaneous recovery after URTI.

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