Background: Olfactory dysfunction is a known clinical feature of multiple sclerosis (MS). Some studies have shown that odor identification impairment is an essential feature associated with cognitive function in MS. This study investigates the relationship between olfactory identification and the disease state, including cognitive function and central brain volume, to evaluate the utility of olfactory identification in the clinical assessment of relapsing-remitting (RR) MS.
Methods: Forty patients with RRMS and 40 healthy controls (HCs) were included. Their olfactory identification was measured using the Odor Stick Identification Test for the Japanese (OSIT-J). Cognitive function was evaluated by the Japanese version of the Wechsler Adult Intelligence Scale, 3rd edition (WAIS-III), and depressive mood was evaluated by the Center for Epidemiologic Studies Depression Scale. Magnetic resonance imaging was used to measure the third ventricle width (3rd VW) as a marker of central brain atrophy.
Results: RRMS patients had a significantly lower OSIT-J score than HCs. The OSIT-J score was significantly lower in RRMS patients with low processing speed (PS) and working memory (WM) scores than RRMS patients with normal PS or WM scores. The OSIT-J score was significantly related to the PS, WM, and the 3rd VW. The OSIT-J score also showed a mild correlation with the expanded disability status scale and disease duration, but not with the number of clinical attacks or patient's age.
Conclusions: Our results suggest that olfactory identification impairment occurs in association with cognitive dysfunction and central brain atrophy. Thus, olfactory identification is a possible disease marker of RRMS as with cognitive impairment, especially PS, reflecting the diffuse neurodegeneration in RRMS.
Keywords: Central brain atrophy; Cognitive function; Information processing speed; Multiple sclerosis; Olfactory identification; Third ventricle width.
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