Effects of olfactory training on patients with parosmia.

Olfactory training (OT) has shown efficacy in improving quantitative olfactory loss (hyposmia), However, its effects on qualitative disorders (parosmia) and the corresponding neural changes remain underexplored. This study aimed to compare the behavioral and neural effects of OT in patients with hyposmia and parosmia using chemosensory event-related potentials (CSERP). Forty-four patients with olfactory dysfunction and twenty-one healthy controls were initially recruited. After accounting for dropouts and exclusions, twenty-two patients (hyposmia: n = 9; parosmia: n = 13) and twenty healthy controls completed both behavioral assessments and CSERP recordings before and after a structured OT program. Behavioral outcomes included Sniffin' Sticks, parosmia test, and well-being ratings. CSERP responses to phenylethyl alcohol (PEA), hydrogen sulfide (H2S), and carbon dioxide (CO2) were recorded via a computer-controlled olfactometer separately for each nostril. Both patient groups showed improved odor identification following OT, and patients with parosmia demonstrated additional benefit in hedonic perception. Moreover, the parosmia symptoms decrease after OT. CSERP results revealed enhanced P1N1 amplitudes in both groups after OT. Notably, patients with parosmia showed reduced P2 latencies in response to PEA, while patients with hyposmia exhibited reduced P2 latencies of H2S in the left nostril. OT benefits both patients with hyposmia and parosmia, though through different behavioral and neural mechanisms. OT reliefs parosmia symptoms, indicating the potential of OT as a promising intervention for patients with parosmia.