To assess olfactory function in individuals with classical (infratentorial) superficial siderosis (iSS)

iSS is a rare but potentially disabling and progressive neurological disorder that commonly involves auditory and vestibular neural pathways. Olfactory nerve function may also be affected but dedicated studies assessing this in iSS are lacking.

Ethics approval was granted. Eleven participants with a known diagnosis of iSS and no prior symptoms or history of COVID-19, were provided with the 40-item (British version) University of Pennsylvania Smell Identification Test (UPSIT) kits by post. The scores (40 as maximum best) were graded as normal, microsmia (mild/moderate/severe) and anosmia, as compared with age- and gender-matched norms; percentile values were obtained. Smoking status was determined; pack-years, years since smoking-cessation and disease duration (from presumed causative event) were calculated.

Ten participants completed the test. The mean (±standard deviation, SD) age was 52.5(±14.5) years; 2 participants (20%) were females; 6 participants (60%) never smoked; 1 participant (10%) was a current smoker. The mean(±SD) UPSIT score was 25.5(±7.8), with no difference between males/females (t(10)=-1.528, p=0.165). The mean(±SD) disease duration (n=9) was 23.2(±11.4) years. The UPSIT scores were statistically significantly lower than age-/gender-matched norms (t(9)=4.016; p=0.003), and below the 30^th centile for all participants (<10th percentile for 4 (40%); in 10-20th percentile for 5 (50%); in 20-30th percentile for 1 (10%)). Six participants (60%) had anosmia or moderate microsmia and 4 (40%) had mild microsmia. There was no correlation (as assessed by Kendall’s tau-b, ?_b) (p>0.05) between the UPSIT scores and: age (?_b(10)=-.114); years since smoking-cessation (?_b(4)=.333), pack-years (?_b(4)=-.333), or disease duration (?_b(9)=.310).

We report a novel quantitative assessment of the prevalence of olfactory dysfunction in iSS. Given its high prevalence, olfactory dysfunction may be another key feature of the iSS clinical syndrome that is currently under-investigated but should routinely be assessed.