We describe a case of autoimmune encephalitis associated with anti-glutamic acid decarboxylase (GAD 65) antibodies in a girl with type 1 Diabetes Mellitus (T1DM).

Anti-GAD65 antibodies are associated with neurological syndromes such as limbic encephalitis, refractory epilepsy, stiff-person syndrome, Miller-Fisher syndrome, cerebellar ataxia, and opsoclonus myoclonus syndrome and non-neurological conditions such as T1DM and thyroiditis. Very few pediatric cases with anti-GAD65 encephalitis are reported to date. Concomitant T1DM is even rarer and complicates management.

A 13 year old girl with developmental delay, ventriculomegaly, hyperglycemia managed with metformin and remote history of seizures, well controlled on topiramate for 5 years, was hospitalized for breakthrough seizures and altered mental status. She had head jerking and generalized convulsion with right temporal electrographic onset; and 3 Hz repetitive eye blinking, initially without electrographic correlate, but later with right temporal electrographic onset. Seizures were initially managed with addition of levetiracetam. As inpatient, she had worsening of mental status and developed diabetic ketoacidosis requiring airway protection. Insulin was started post clinical diagnosis of T1DM. Clinical and electrographic seizures worsened in frequency. Interictal EEG showed independent bilateral frontal; left temporal spikes; independent right temporal periodic lateralized epileptiform discharges; and multifocal stimulus-induced rhythmic, periodic, or ictal discharges. Addition of fosphenytoin, lacosamide and continuous midazolam infusion could not control seizures. Infectious work-up was non-revealing. Anti-GAD65 antibody levels were elevated in serum (207 nmol/L) and CSF (24 nmol/L). No other testable autoimmune antibodies were detected. Intravenous high dose corticosteroids and intravenous immunoglobulin resulted in complete resolution of clinical and electrographic seizures but minimal improvement in her mental status. Plasma exchange (PLEX) improved mental status. She is receiving further rounds of PLEX.

Physicians should be aware of this rare entity of anti-GAD65 encephalitis. This can occur in conjunction with T1DM. Prompt recognition and aggressive immunological treatment is critical.