GABABR IgG Associated Encephalitis: Clinical Presentations and Measures to Improve Diagnostic Assay Specificity

Objective To review the clinical/oncological presentations of gamma aminobutyric acid-B receptor (GABABR)-IgG and evaluate clinical specificity antibody testing methodologies. Background GABABR-IgG is an intermediate-risk paraneoplastic autoantibody commonly associated with encephalitis and/or seizures. Design/Methods positive patients tested at Mayo Clinic Neuroimmunology Laboratory were identified. Available archived sera retested by cell-based assay (CBA) 1:10 1:100 dilutions. Results 105 seropositive details identified (females, n = 56; median age 63 [range 8-82]). Most had one three anti-GABABR encephalitis/seizure presentations: focal-onset seizures altered mental status (n 39), new-onset refractory epilepticus (NORSE [n 23]) or rapidly progressive dementia 14). Fifty-three 72 (74%) available data malignancy, primarily small cell lung cancer (SCLC). Two P/Q type VGCC-IgG isolated Lambert-Eaton Myasthenic Syndrome. Additionally, 27 presented non-specific symptoms alternate diagnoses (atypical presentation); none underlying SCLC (13 malignancy data). detected in CSF (95%, 52/55; 3 who negative, 1 NMDA-IgG another AMPA-IgG CRMP5-IgG) CBA serum a dilution (76%, 31/41). Five only serum. Forty-eight 76 samples on tissue IFA (serum 17/42, 40/49). Among atypical presentations, most did not have positivity (91%, 21/23) titer (0/17). None cases 0/27, 0/21). Conclusions autoimmune presentations. Our study highlights importance evaluating both dilutions, as seropositivity without has poor specificity.