Characterization of Anti-GAD65-Associated Neurological Syndromes: Clinical Features and Antibody Titers.

Introduction: Anti-GAD65 antibodies are associated with several neurological phenotypes. Antibody titers are increasingly recognized as useful in diagnosis and prognosis.

Objective: To describe a Portuguese cohort of patients with anti-GAD65-associated neurological syndromes.

Methods: Retrospective analysis of all patients with positive anti-GAD65 antibodies and associated neurological syndromes followed in a tertiary referral center.

Results: Nineteen anti-GAD65 antibody-positive neurological patients were identified, 62.3% female, with a mean age of onset of 56.0 (SD = 13.3) years. Comorbid autoimmune disorders were present in seven patients. Six patients had limbic encephalitis (31.6%), four had epilepsy (21.1%), four had cerebellar ataxia (21.1%), and three had stiff-person syndrome (15.8%). Two patients presented with isolated cognitive dysfunction (executive and mnesic) in the absence of other neurological symptoms. The mean follow-up time was 24.0 (14.0-42.0) months, at the end of which the mean modified Rankin Scale (mRS) value was 2.0 (1.0-4.0). Screening for malignancies was negative in all patients. Serum quantitative analysis was carried out in 18 patients, 10 of whom showed titers above previously defined cut-off points (>10,000 IU/L for ELISA and >20 mmol/L for RIA). Quantitative CSF analysis was performed in nine patients, with four showing above-threshold titers. There was no association between anti-GAD65 levels and clinical phenotype or the final mRS values. High-dose intravenous methylprednisolone and oral prednisolone were the most common acute and chronic treatment regimens, respectively.

Conclusion: Anti-GAD65 antibodies are associated with varied neurological syndromes, and antibody titers alone should not be used to exclude a disease.