Clinical correlates of olfactory dysfunction in spinocerebellar ataxia type 3

Olfactory dysfunction is a very common and early sign in neurodegenerative disorders, but few data are already available in hereditary ataxias. Our aim was to evaluate the sense of smell in patients with molecular-proven spinocerebellar ataxia type 3 (SCA3). Forty-one patients with SCA3 and 46 control subjects were studied. The sense of smell was tested using the Sniffin's Sticks (SS-16). We also evaluated Mini-Mental State Examination (MMSE) and non-cerebellar symptoms, such as parkinsonism, dystonia, and restless legs syndrome (RLS). The SCA3 group had significantly lower SS-16 scores than controls (11.5 ± 2.4 vs 12.8 ± 1.5, p = 0.003). Multiple linear regression analyses, controlling for age, sex, education, cigarette smoking, and MMSE scores, showed that SCA3 (p = 0.021), sex (p = 0.003) and MMSE scores (p = 0.002) had significant regression coefficients. All the variables taken together were significantly associated with the SS-16 scores (p ≤ 0.001). Although MMSE scores and female sex were stronger predictors of the SS-16 scores than SCA3, subjects with SCA3 had lower scores on the SS-16, regardless of sex or MMSE scores. Additionally, MMSE scores, sex and presence of RLS were the best predictors of SS-16 scores. Overall, our results strengthen that the sense of smell is significantly reduced in patients with SCA3 and that sex, MMSE scores and RLS also influence the SS-16 scores.