Olfactory impairment in autoimmune encephalitis: another piece of the puzzle

Abstract

Background Despite being long neglected, olfaction has recently become a focus of intense research in neuroscience, as smell impairment has been consistently documented in both neurodegenerative and neuroinflammatory diseases. Considering the close anatomo-functional correlations between the limbic system and the central olfactory structures, we investigated olfaction in a population of patients with autoimmune encephalitis (AE). Methods Nineteen adult subjects (14 males, median age 64 years) diagnosed with definite (14/19) or possible (5/19) AE and followed for ≥ 6 months were enrolled. The Brief Smell Identification Test (B-SIT), a 12-item, forced-choice, scratch-and-sniff measure, was used to assess the patients’ olfactory function in comparison with a group of sex- and age-matched healthy controls (HC). According to the B-SIT score, subjects were classified as anosmic (< 6), hyposmic (6–8) and normal (≥ 9). Electro-clinical, laboratory and neuroimaging findings were reviewed. Results Smell impairment was revealed in 15/19 patients (9 hyposmic, 6 anosmic), compared with 5/19 HC ( p = 0.0029). Age, gender and smoking habits did not affect the participants’ performance at B-SIT. Olfactory dysfunction appeared more common among patients with definite AE ( p = 0.0374), regardless of autoantibody status. Subjects with higher modified Rankin Scale (mRS) scores at AE onset more likely presented hyposmia/anosmia ( p = 0.033), and so did those with bilateral ictal/interictal EEG abnormalities ( p = 0.006). Conclusions We found olfaction to be impaired in a significantly large proportion of AE cases. Smell deficits appeared more common in subjects with severe AE (as indicated by both definite diagnosis and higher mRS score), and might represent an additional feature of immune-mediated encephalitis. Supplementary Information The online version contains supplementary material available at 10.1007/s00415-022-10959-6.

Olfaction and Mobility in Older Adults

“…Each correct answer receives 1 point, and the total score ranges from 0 to 12, with a lower score indicating a poorer sense of smell. In this analysis, we defined anosmia as a B-SIT score of 0 to 6, hyposmia as 7 to 8, moderate olfaction as 9 to 10, and good olfaction as 11 to 12, which was consistent with other studies …”

Olfactory dysfunction after autoimmune encephalitis depending on the antibody type and limbic MRI pathologies

“…Olfactory dysfunction may be associated with AE. This has recently been suggested by two studies investigating olfactory function in AE patients (4,5). In contrast to these studies, which reported impaired olfactory function in most AE patients, in our AE cohort, overall olfactory function was not significantly impaired compared to a standard population.…”

“…Morano et al detected olfactory dysfunction in 15/19 of AE patients (5). However, because of the different test-design used (Brief Smell Identification Test, B-SIT), only the olfactory identification can be compared.…”

“…In another work by Morano et al, olfactory dysfunction was found in 15 of 19 AE patients (5). The heterogeneity of the groups was high with 12 different antibody-types including seronegative AE in the first sample (4) and 5 different antibody-types in the second sample (5). Considering that different AE antibody-types are associated with a spectrum of clinical syndromes, olfactory function may be differentially affected in known AE subtypes.…”

“…In 2019 Geran et al showed in a cohort of 32 AE patients, that olfactory dysfunction is present in 75% of AE patients (4). In another work by Morano et al, olfactory dysfunction was found in 15 of 19 AE patients (5). The heterogeneity of the groups was high with 12 different antibody-types including seronegative AE in the first sample (4) and 5 different antibody-types in the second sample (5).…”