Autoimmune encephalitis and gastrointestinal inflammation: Building evidence for a gut-brain connection.

OBJECTIVE: To report coexistence of autoimmune encephalitis (AE) and gastrointestinal inflammatory pathology, including malignancy. METHODS: We performed a retrospective observational case series of patients seen at Massachusetts General Brigham and University of Pittsburgh Medical Center during routine clinical care for AE, who had coexisting gastrointestinal inflammatory pathology. Clinical, paraclinical, treatment, and outcome data were reviewed. RESULTS: Sixteen patients (44% female, median age 64 years) with AE and gastrointestinal inflammatory pathology were identified. Presenting neurologic features included cognitive dysfunction (50%), seizures (44%), and psychiatric symptoms (44%). Clinically congruent neural autoantibodies were identified in 9/16 patients (56%) (GFAP, n = 3; LGI1, n = 3; GAD65, n = 1; PCA-1, n = 1; PCA-2, n = 1). Brain MRI abnormalities were present in 8/16 (50%), CSF pleocytosis in 6/16 (38%), elevated CSF protein in 7/16 (44%), CSF-unique oligoclonal bands in 3/10 tested (30%), and matched bands in 6/10 tested (60%). Gastrointestinal pathology included gastrointestinal tumor in 5/16 (31%) and inflammatory bowel disease in 4/16 (25%). AE followed gastrointestinal disease in 7/16 patients (44%), was diagnosed concurrently in 7/16 (44%), and preceded gastrointestinal disease in 2/16 (12%). Gastrointestinal symptoms or imaging findings were present at the onset of neurologic symptoms in 81% of patients. Fifteen of 16 patients (94%) received immunotherapy, and 12/16 (75%) had a modified Rankin Scale score of 0-2 at last follow-up. All deaths (3/16; 19%) occurred in patients with metastatic gastrointestinal malignancy. CONCLUSIONS: This case series expands upon limited related literature and explores potential gut-brain immune associations in a subset of patients with AE.