Abstract
Objective: To test the hypothesis that olfactory (OF) and gustatory function (GF) is disturbed in patients with autoimmune encephalitides (AE).Methods: The orthonasal OF was tested in 32 patients with AE and 32 age- and sex-matched healthy controls (HC) with the standardized Threshold Discrimination Identification (TDI) score. This validated olfactory testing method yields individual scores for olfactory threshold (T), odor discrimination (D), and identification (I), along with a composite TDI score. The GF was determined by the Taste Strip Test (TST).Results: Overall, 24/32 (75%) of patients with AE, but none of 32 HC (p < 0.001) had olfactory dysfunction in TDI testing. The results of the threshold, discrimination and identification subtests were significantly reduced in patients with AE compared to HC (all p < 0.001). Assessed by TST, 5/19 (26.3%) of patients with AE, but none of 19 HC presented a significant limitation in GF (p < 0.001). The TDI score was correlated with the subjective estimation of the olfactory capacity on a visual analog scale (VAS; rs = 0.475, p = 0.008). Neither age, sex, modified Rankin Scale nor disease duration were associated with the composite TDI score.Conclusions: This is the first study investigating OF and GF in AE patients. According to unblinded assessment, patients with AE have a reduced olfactory and gustatory capacity compared to HC, suggesting that olfactory and gustatory dysfunction are hitherto unrecognized symptoms in AE. Further studies with larger number of AE patients would be of interest to verify our results.
Highlights
In recent years, the term autoimmune encephalitis was established for a heterogeneous group of antibody-associated disorders of the brain that can either be caused by paraneoplastic or non-paraneoplastic conditions [1, 2]
As the olfactory information is processed in these brain areas, we hypothesized that functional disturbances of the limbic system in AE patients could lead to olfactory and gustatory dysfunction [11, 12]
The GF was significantly limited in 26.3% (5/19) of AE patients in the TST and none of the HC (p < 0.001)
Summary
The term autoimmune encephalitis was established for a heterogeneous group of antibody-associated disorders of the brain that can either be caused by paraneoplastic or non-paraneoplastic conditions [1, 2]. The diagnosis of definite autoimmune limbic encephalitis can be made, if the following criteria are met: MRI abnormalities of the medial temporal lobe, epileptic slow-waves on EEG, and CSF pleocytosis [3]. Olfactory dysfunction is an increasingly detected symptom in neuroimmunological disorders such as multiple sclerosis and neuromyelitis optica spectrum disorder [8, 9]. As the olfactory information is processed in these brain areas, we hypothesized that functional disturbances of the limbic system in AE patients could lead to olfactory and gustatory dysfunction [11, 12]. Emotional and behavioral consequences of olfactory, and gustatory dysfunction, its detection using a standardized test could be a helpful marker of disease activity [13]
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