Anti-GAD antibody syndrome with concomitant cerebellar ataxia, stiff person syndrome, and limbic encephalitis.

Abstract

A 42-year-old man initially presented at age 38 with progressive vertigo, leg stiffness, dysarthria, diplopia, and ataxia. Lumbar puncture revealed 1 red blood cell and 9 nucleated cells (96% lymphocytes) with normal protein and glucose. Anti–glutamic acid decarboxylase (GAD) antibody testing was strongly positive at 1,050 nmol/mL (November 2009 by immunoprecipitation assay, Mayo Clinic, reference range (RR) ≤ 0.02 nmol/mL). MRI brain was unremarkable. He was diagnosed with stiff person syndrome (SPS), autoimmune cerebellar ataxia (CA), type 1 diabetes mellitus (DM1), and Hashimoto thyroiditis. He was treated with high-dose methylprednisolone for 3 days, IV immunoglobulin (IVIg) 2 g/kg divided over 2 days, and monthly IVIg for 3 months, with persistently high anti-GAD antibody level after treatment (1,070 nmol/mL in February 2010).