Differences between orthonasal and retronasal olfactory functions in patients with loss of the sense of smell.

OBJECTIVE

To investigate differences between orthonasal and retronasal olfaction in patients with loss of the sense of smell without taste complaints.

DESIGN

Electrophysiological and psychophysical testing of orthonasal and retronasal olfactory functions.

SETTING

Outpatient clinics.

PATIENTS

A series of 18 patients who had olfactory loss due to various reasons but no "taste" complaints.

MAIN OUTCOME MEASURES

Orthonasal and retronasal olfactory functions assessed by olfactory event-related potentials and psychophysical smell tests.

RESULTS

Psychophysical testing revealed retronasal olfaction to be normal or slightly altered, whereas orthonasal olfaction was either absent or severely compromised. Findings from nasal endoscopic examinations and computed tomographic scans were within the reference range in all subjects. In response to orthonasal stimulation there were neither detectable olfactory event-related potentials nor any with small amplitudes, whereas olfactory event-related potentials in response to retronasal stimulation were clearly present in some patients.

CONCLUSION

These clinical observations, together with the psychophysical and electrophysiological findings, suggest that orthonasal and retronasal olfaction might be processed differently.