Metabolic phenotyping of pilomotor seizures in autoimmune encephalitis

OBJECTIVES: Ictal piloerection (IP) is an uncommon symptom in focal epilepsy and is associated with autoimmune encephalitis (AE). However, the networks involved in AE‐associated IP are still unclear. To have a better understanding of IP underlying mechanisms, the current study investigated whole‐brain metabolic networks for the analysis of AE‐associated IP. METHODS: Patients with AE and IP diagnosed at our Institute between 2018 and 2022 were selected. We then investigated the brain regions associated with AE‐associated IP using positron emission tomography (PET). Anatomometabolic changes (interictal (18)F fluorodeoxyglucose PET) in AE patients with IP were compared with those of AE patients of similar age without IP (p‐voxel <0.001, uncorrected). RESULTS: Sixteen patients showed significant IP. The overall IP prevalence was 4.09% of patients with AE and 12.9% of patients with limbic encephalitis. The most common autoantibodies were against LGI1 (68.8%) followed by GAD65 (6.3%), NMDA (6.3%), GABAb (6.3%), CASPR2 (6.3%), and antibodies recognizing both GAD65 and mGLUR5 (6.3%). Most patients responded well to immunotherapy. Analysis of the imaging results at the voxel level showed that patients with IP had hypermetabolic changes in the right inferior temporal gyrus, suggesting involvement of this brain region in IP. CONCLUSIONS: Our findings indicate that IP as an uncommon AE‐associated manifestations should be recognized. We observed that the metabolic pattern of IP was conspicuous in the right inferior temporal gyrus.