Research Reports - Olfactory identification and its relationship to executive functions, memory, and disability one year after severe traumatic brain injury

Neuropsychology. 2016 Jan;30(1):98-108. doi: 10.1037/neu0000206. Epub 2015 Jun

Sigurdardottir S(1), Andelic N(2), Skandsen T(3), Anke A(4), Roe C(5), Holthe
OO(5), Wehling E(6).

OBJECTIVE: To explore the frequency of posttraumatic olfactory (dys)function 1
year after severe traumatic brain injury (TBI) and determine whether there is a
relationship between olfactory identification and neuropsychological test
performance, injury severity and TBI-related disability.
METHOD: A population-based multicenter study including 129 individuals with
severe TBI (99 males; 16 to 85 years of age) that could accomplish
neuropsychological examinations. Olfactory (dys)function (anosmia, hyposmia,
normosmia) was assessed by the University of Pennsylvania Smell Identification
Test (UPSIT) or the Brief Smell Identification Test (B-SIT). Three tests of the
Delis-Kaplan Executive Function System (D-KEFS) were used to assess processing
speed, verbal fluency, inhibition and set-shifting, and the California Verbal
Learning Test-II was used to examine verbal memory. The Glasgow Outcome
Scale-Extended (GOSE) was used to measure disability level.
RESULTS: Employing 2 different smell tests in 2 equal-sized subsamples, the UPSIT
sample (n = 65) classified 34% with anosmia and 52% with hyposmia, while the
B-SIT sample (n = 64) classified 20% with anosmia and 9% with hyposmia.
Individuals classified with anosmia by the B-SIT showed significantly lower
scores for set-shifting, category switching fluency and delayed verbal memory
compared to hyposmia and normosmia groups. Only the B-SIT scores were
significantly correlated with neuropsychological performance and GOSE scores.
Brain injury severity (Rotterdam CT score) and subarachnoid hemorrhage were
related to anosmia. Individuals classified with anosmia demonstrated similar
disability as those with hyposmia/normosmia.
CONCLUSIONS: Different measures of olfaction may yield different estimates of
anosmia. Nevertheless, around 1 third of individuals with severe TBI suffered
from anosmia, which may also indicate poorer cognitive outcome.

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