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Abstract

Objective

Although olfaction is often compromised by such factors as head trauma, viruses, and toxic agents, the olfactory epithelium and sectors of the olfactory bulb have the potential for regeneration. This study assessed the degree to which olfactory function changes over time in patients presenting to a university-based smell and taste center with complaints of olfactory dysfunction and the influences of etiology (eg, head trauma, upper respiratory infection), sex, age, smoking behavior, degree of initial dysfunction, and other factors on such change.

Methods

Well-validated odor identification tests were administered to 542 patients on 2 occasions separated from one another by 3 months to 24 years. Multivariable regression and χ2 analyses assessed the influences of the variables on the longitudinal changes in olfactory test scores.

Results

On average, smell test scores improved modestly over time. Patient age, severity of initial olfactory loss, and the duration of dysfunction at first testing were significant predictors of the amount of the change. Etiology, sex, time between the two test administrations, and initial smoking behavior were not significant predictors. The percentage of anosmic and microsmic patients exhibiting statistically significant change in function was 56.72 and 42.86%, respectively. However, only 11.31% of anosmic and 23.31% of microsmic patients regained normal age-related function over time.

Interpretation

Some recovery can be expected in a significant number of patients who experience smell loss. The amount of recovery depends on the degree of initial loss, age, and the duration of loss. Etiology, per se, is not a significant determinant of prognosis, in contrast with what is commonly believed. Ann Neurol 2007