AUTHOR=Hänsel Martin , Schmitz-Peiffer Henning , Hähner Antje , Reichmann Heinz , Schneider Hauke 

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

JOURNAL=Frontiers in Neurology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/neurology/articles/10.3389/fneur.2023.1225975

DOI=10.3389/fneur.2023.1225975

ISSN=1664-2295

ABSTRACT=<sec id="sec1"><title>Objective</title><p>Patients’ olfactory function after autoimmune encephalitis (AE) involving limbic structures may be impaired. This study aimed to characterize olfactory function in patients after autoimmune encephalitides.</p></sec><sec id="sec2"><title>Methods</title><p>A case–control study was performed including 11 AE patients with antibodies against NMDAR (<italic>n</italic> = 4), GAD (<italic>n</italic> = 3), VGKC (<italic>n</italic> = 3) and antibody-negative AE (<italic>n</italic> = 1) and a control group of 12 patients with pneumococcal meningo-encephalitis (PC). In subgroup analyses, AE patients with and without NMDAR-antibodies were compared. Olfactory function was assessed using the Sniffin Sticks test and the resulting TDI-score (threshold, discrimination, identification). Involvement of limbic structures was evaluated on imaging data (MRI). Statistical analyses were performed to test for correlations of TDI-score and MRI results.</p></sec><sec id="sec3"><title>Results</title><p>The overall olfactory function of the AE-group and the PC-group was comparable (mean TDI 32.0 [CI 27.3–36.7], 32.3 [CI 28.5–36.0)]. The proportions of hyposmic patients were similar compared to the general population. However, AE patients of the non-NMDAR group had significantly lower TDI-scores (28.9 ± 6,8) than NMDAR patients (37.4 ± 3.5) (<italic>p</italic> = 0.046) and a significantly lower discrimination capability than the NMDAR patients (9.9 ± 2.0 vs. 14.5 ± 0.6) (<italic>p</italic> = 0.002). The non-NMDAR patients had significantly more limbic MRI pathologies (6/7) compared to the NMDAR patients (0/4) (<italic>p</italic> = 0.015). Furthermore, a correlation between limbic MRI pathologies and worse capability of smelling discrimination was found (<italic>p</italic> = 0.016, <italic>r</italic> = −0.704, <italic>n</italic> = 11).</p></sec><sec id="sec4"><title>Conclusion</title><p>Our results indicate that patients with NMDAR autoimmune encephalitis have normal long term olfactory function. However, patients with non-NMDAR autoimmune encephalitis appear to have a persistently impaired olfactory function, probably mediated by encephalitic damage to limbic structures.</p></sec>