The incidence of anosmia after traumatic brain injury: the SHEFBIT cohort.

BACKGROUND: While anosmia is common after Traumatic Brain Injury(TBI) (prevalence 4%-68%),studies differ in the associations found with other variables.

AIMS: To assess the incidence of anosmia within a large, mixed TBI cohort and examine relationships with other injury or demographic features, including depression and global outcome(GOSE).

DESIGN, SUBJECTS AND SETTING: 774 consecutive TBI admissions over 2 years, assessed within a specialist neurorehabilitation clinic.

METHODS: All patients assessed at 6-8 weeks and 1 year. Tools included the Extended Glasgow Outcome Scale(GOSE), Rivermead Head Injury Follow-up Questionnaire, Rivermead Post-Concussion Symptoms and the Hospital Anxiety and Depression Score. Olfactory function assessed with sensitivity to coffee granules.

RESULTS: The overall incidence of anosmia was 19.7%; mild TBI (9.55%), moderate (20.01%), and severe (43.5%). On a logistic regression, features of TBI severity (p < 0.001 (95% CI 0.098-0.438)), medical comorbidities (p = 0.026 (95% CI 0.301-0.927)) and depression (p = 0.006 (95% CI 1.202-2.981)) were significant. Sixty percent of patients with anosmia at 1 year were found to be clinically depressed, compared to 36% of patients without anosmia.

CONCLUSION: In the largest prospective study of post-TBI anosmia, the incidence increased with TBI severity and other medical illness. The presence of anosmia should also raise the clinical suspicion of depression.