The expanding spectrum of pediatric anti-glutamic acid decarboxylase antibody mediated CNS disease - a chance association?

Central nervous system autoimmunity in the pediatric age group represents an evolving constellation of various syndromes distinct from the adult age group. One of the rarely described pathogenic auto-antibodies (ab) is the one directed against glutamic acid decarboxylase (GAD). While its pathogenic role is controversial, literature concerning adult patients abounds with heterogeneous presentations with epilepsy often as part of limbic encephalitis or chronic temporal lobe epilepsy and cerebellar ataxia accompanying endocrinopathies or paraneoplastic disorders. Diagnosis is often delayed until late adulthood. The authors report hitherto under-reported syndromes in the pediatric age group. The first case was a 3-year-old boy with sub-acute myoclonus-ataxia following a flu-like illness akin to para-infectious cerebellitis. The second case was a 7-year-old girl with longstanding chronic extratemporal partial epilepsy and electrical status epilepticus in sleep (ESES) with right hemiparesis and developmental delay. Investigations revealed two-four fold elevations in titres of GAD-65-ab. The absence of systemic diseases like diabetes and the dramatic clinical response to steroids as well as intravenous immunoglobulin in both the cases argued for GAD-ab mediated neuronal injury rather than a chance association. The concern exists regarding other potentially co-existent auto-ab to gamma-amino butyric acid and glycine receptors, and demonstration of intrathecal synthesis of GADab would be ideal. This entity should be contemplated in children presenting with acute/ sub-acute onset episodic or progressive ataxia or refractory cryptogenic focal epilepsy syndromes, epileptic encephalopathy such as ESES and worsening neurological deficits. These children ought to be maintained on regular follow-up for monitoring evolution of other autoimmune disorders in adult life.