Clinical assessment of retronasal olfactory function

Objectives: To develop a test kit for the simple assessment of retronasal olfactory function and to compare orthonasal and retronasal olfactory function in healthy subjects and patients with olfactory disorders. Design and Patients: We tested 230 individuals with normosmia, hyposmia, and anosmia using grocery-available powders. Initially, 30 different substances were investigated. Subjects identified each substance using a list with 4 verbal items (forced choice). After preliminary experiments, 20 items were selected according to the degree to which they were identified by normosmic and anosmic subjects. Orthonasal olfactory function was assessed psychophysically using "sniffin' sticks," which includes tests for odor identification, discrimination, and butanol odor thresholds. In addition, anosmia was confirmed electrophysiologically by means of olfactory-evoked potentials. Results: In healthy subjects, there was a test-retest reliability correlation of r(27)=0.76 for retronasal olfactory function, which is similar to other odor identification tests. Retronasal testing in normosmic subjects allowed for the discrimination of sex-related differences, with women scoring higher than men (P=.007), and the identification of a slight decrease with age (r(120)=-0.20; P=.03). Orthonasal and retronasal identification of odors was found to correlate (r(86)=0.78; P<.001). Retronasal testing allowed for the discrimination between normosmia, hyposmia, and anosmia (P<.001). In addition, retronasal performance of anosmic patients appeared to improve with duration of anosmia (P=.03). No difference was found between patients with anosmia of different origin. Conclusion: Results of the present investigation indicate that the assessment of retronasal olfactory function is possible using oral stimulus presentation.