Glutamic acid decarboxylase isotype 65 (GAD-65) antibodies have been associated with several conditions including type 1 diabetes (T1D), stiff-man syndrome and autoimmune cerebellar ataxia. GAD-65 antibody-associated cerebellar ataxia has been described in multiple case reports, mostly in adult women, but rarely in children, as reported here.
An 11-year-old female presented with two weeks of polyuria and polydipsia and one week of abnormal speech and difficulty walking. Labs were consistent with new onset diabetes with mild ketoacidosis. Neurological exam localized her lesion to the cerebellum. Several type 1 diabetes-related antibodies were positive, including zinc transporter 8, GAD-65, and ICA512. Insulin autoantibody was negative. Serum Pediatric Autoimmune Central Nervous System Disorders Evaluation (Mayo Clinic) showed only elevated levels of GAD-65 antibody to 41.6 nmol/L (≤ 0.02). CSF studies showed oligoclonal bands, without evidence of infection. CSF GAD-65 antibody testing (Mayo Clinic) was elevated to 13.7 nmol/L (≤ 0.02). MRI showed no cerebellar pathology. Thyroglobulin and thyroid peroxidase antibodies were normal. Because of the constellation of findings, she was diagnosed with GAD-65 antibody-associated cerebellar ataxia. Her symptoms improved after a short course of steroids and IVIG. She is planned for monthly IVIG for at least 6 months.
Elevated serum GAD-65 antibody levels are found in the majority of patients newly diagnosed with T1D. GAD-65 CSF levels are noted to be higher in patients that develop autoimmune cerebellar ataxia, stiff-man syndrome or autoimmune polyendocrine syndromes (≤20 nmol/L), as seen in this patient (41.6 nmol/L). Patients presenting with new onset T1D and cerebellar ataxia should prompt evaluation for GAD-65 antibody-associated cerebellar ataxia.
K. Chan: None. M. Sweat: None. M. R. Zimbric: None. R. S. Newfield: Consultant; Self; Merck Sharp & Dohme Corp.