Abstracts

Rationale: Elevated titers of antibodies against glutamic acid decarboxylase (GAD) 65 present with diverse clinical  and phenomenological syndromes, including stiff person syndrome, cerebellar ataxia, autoimmune epilepsies, limbic encephalitis, syndromes of cryptogenic refractory status epilepticus, and type 1 diabetes mellitus. Many patients to improve after immunotherapy. Syndromes associated with anti-GAD65 antibodies are rarely reported in children.  Methods: We describe the case of a 7-year-old girl who was previously healthy and intellectually normal. She presented with new onset two focal seizures a few days apart. She had limb-shaking and jaw clenching with decreased level of consciousness lasting about five minutes. Her seizures were controlled with levetiracetam After this presentation, she also developed new onset bilateral continuous, high frequency, semirhythmic facial muscle myoclonus, prominently involving the right face and upper lip during both wakefulness and sleep. She reported a headache over the right temporal area initially which resolved spontaneously. Six weeks into her course, she developed segmental myoclonus involving the right hand, particularly the thumb, tongue and palate. These movements affected her swallowing transiently but breathing and speech were intact. She never had any signs of encephalopathy, cognitive changes or regression in her school performance.Investigation shows slightly elevated cerebrospinal fluid (CSF) protein (at 0.29 grams/L, Normal range 0.12-0.24) and cell count (8 cells, 97% lymphocytes, Normal range 0-7). Oligoclonal bands were positive. GAD 65 antibodies were positive in CSF and serum (>250 IU/ml). Other autoimmune encephalitis antibody panel were otherwise negative.  Metabolic investigation including neuronal ceroid lipofuscinosis types 1 and 2, ammonia, lactate, transferrin isoelectric focusing were all negative. Neoplastic, paraneoplastic and autoimmune work up were negative.Initial EEG showed facial muscle twitching without any EEG correlate and occasional epileptiform discharges over the left posterior quadrant. Repeated EEG after 2 months showed frequent left temporal epileptiform activity and giant occipital photic response at low frequency stimulation. EMG showed bilateral semirhythmic facial muscle discharges with no evidence of fasciculation or myokymia. Initial MRI was unremarkable. Repeated MRI after 1.5 months showed T2 hyperintensity in the left medial temporal lobe and repeated MRI after 3 months showed T2 signal abnormality in the bilateral medial temporal lobes. MRI scan of body was negative.She was started on high dose IV steroids for 5 days then oral steroid course, intravenous immunoglobulin (IVIg) course biweekly, and 2 doses of rituximab. On day 5 of treatment the myoclonus improved clinically.  Results: We report a novel presentation of GAD 65 antibody syndrome associated with myoclonus in a child.  Conclusions: To facilitate early diagnosis, a high level of suspicion for GAD 65 antibody-related CNS disease needs be maintained as this can prompt early treatment and may lead to better outcomes.  Funding: None