Abnormalities of axon growth in human olfactory mucosa.
OBJECTIVE
Random biopsies of the human adult olfactory mucosa often demonstrate degenerative changes in the olfactory epithelium (OE) in both dysosmic and normosmic patients and, consequently, have limited diagnostic usefulness. However, detailed analysis of the subepithelial tissue with specific attention to the fascicles of the olfactory nerve and abnormalities of axonal growth may improve the correlation of histopathology with sensory function.


METHODS
Retrospective review of human OE biopsies.


METHODS
Mucosal biopsies from the olfactory area obtained from 27 subjects were examined by light and electron microscopy, with particular attention to the olfactory nerve fascicles; results were correlated with clinical status. Immunohistochemical analysis was used to characterize the extent of axonal depletion, relative maturity of the parent population, and aberrant axonal growth.


RESULTS
As expected, there are areas of respiratory metaplasia and neuronal depletion in normosmic as well as dysosmic patients. The degree of axon degeneration within the fascicles correlates better with individual olfactory status. Immature neurons predominate, and re-entrant neuromas develop in patients with olfactory loss caused by disconnection from the olfactory bulb. Individuals with olfactory loss caused by epithelial damage as with chronic rhinosinusitis display evidence of nerve fascicle degeneration and intraepithelial neuromas.


CONCLUSIONS
The status of olfactory axons provides useful information on the overall condition of the olfactory periphery and improves the diagnostic usefulness of mucosal biopsies. In addition to an assessment of the epithelium per se, the fascicles of the olfactory nerve need to be characterized for a complete analysis of the olfactory mucosa.
Holbrook
Eric H
EH
Department of Otolaryngology, MA Eye and Ear Infirmary, and Department of Otology and Laryngology, Harvard Medical School, Boston, Massachusetts 02114, USA. eric_holbrook@meei.harvard.edu
Leopold
Donald A
DA
Schwob
James E
JE
D000328:Adult; D000368:Aged; D001369:Axons / Q000648:ultrastructure*; D001706:Biopsy; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D008297:Male; D008854:Microscopy, Electron; D008875:Middle Aged; D009463:Neuroma / Q000473:pathology; D009669:Nose Neoplasms / Q000473:pathology; D000857:Olfaction Disorders / Q000175:diagnosis; D009831:Olfactory Mucosa / Q000294:innervation* / Q000648:ultrastructure; D009832:Olfactory Nerve / Q000648:ultrastructure