Objectives/hypothesis: The aim of the present study was to evaluate the course of olfactory dysfunction in patients with olfactory loss following infections of the upper respiratory tract.
Study design: Prospective cohort.
Methods: A total of 27 patients were included; each patient was evaluated twice. Psychophysical testing of olfactory function was performed with the Sniffin' Sticks test and chemosensory functions with event-related potential (ERP).
Results: At T1, 15 patients were considered hyposmic, 12 as anosmic. Accordingly, nine and 27 patients demonstrated olfactory ERP. At T2, 16 and 11 patients were considered as hyposmic and anosmic, and 11 demonstrated olfactory ERP. Analysis of variance did not show significant differences for any parameters between T1 and T2: threshold, discrimination, identification (TDI) scores at the Sniffin' Sticks and amplitudes and latencies of N1 and P2 in the ERP. However, seven patients demonstrated an increase of more or equal to six points at the TDI score, indicating significant improvement. Four of the seven patients had olfactory ERP at T1 (57%); of those patients who did not show improvement, five of 20 (25%) exhibited olfactory ERP. Thus, the presence of olfactory ERP predicts a positive evolution of olfactory function with a relatively high specificity of 83%.
Conclusions: The current findings clearly confirm earlier results on recovery rate of postinfectious olfactory loss. The new finding is that the presence of olfactory ERP at the first consultation is also a positive predictive factor of a favorable outcome in this disease.