A healthy 29-month-old boy presented with 1-week history of bizarre psychiatric symptoms that progressed to behavioral aggression, insomnia, and disuse of the left upper extremity that were thought to be seizures.
He had episodic outbursts of excessive, inconsolable crying and distress that were described "as though he was having nightmares while awake". He had delayed sleep onset from his baseline, decreased appetite, decreased activity level, and emesis. Subsequently, he had dysarthria with progressively decreasing verbal output to the point of mutism with preserved comprehension.
Cranial nerves, muscle bulk and strength, and reflexes were normal. His tone was episodically increased in the left upper extremity with prominent intermittent dystonia and positive Babinski response on left plantar stimulation. Sensory exam was normal to pin prick and vibration. Gait was initially normal but progressively worsened to significant ataxia and frequent falls when trying to stand or ambulate unassisted.
Past history was significant for streptococcal-negative pharyngitis and a motor vehicle accident. The accident occurred at age 19 months when he sustained a pneumothorax that fully recovered. His development was normal, described as an independent, mild-mannered and active toddler. Pregnancy, birth, and family histories were unremarkable.
Because of suspicion of seizures and status epilepticus, an urgent EEG was obtained that captured movements and showed them to be nonepileptic seizure mimics consisting of unilateral extremity quasi-rhythmic movements, and AEDs were withheld.
Cerebrospinal fluid analysis showed 8 WBC and 450 red blood cells without xanthochromia. Cerebrospinal fluid protein was 26 mg/dL, and cerebrospinal lactate and glucose were normal. Cerebrospinal fluid herpes and enterovirus amplifications were negative. Blood counts, chemistries, and urine drug screen were unremarkable. Antistreptolysin O, antinuclear antibody, lupus anticoagulant, cytoplasmic-antineutrophil cytoplasmic antibodies, perinuclear-antineutrophil cytoplasmic antibodies, and antiphospholipid antibody titers, thyroid function studies, creatine kinase, lactic acid, and serum ammonia were normal as were serum amino and urine organic acids, carnitine, and acylcarnitine. Cerebral MRI, EEG, echocardiography, and abdominal ultrasound were normal.
Given his progressive neurological deterioration as well as prominent motor and psychiatric manifestations, an empiric diagnosis of autoimmune-mediated encephalitis was made (and confirmed two weeks later). An empiric trial of intravenous immunoglobulin of 2 g/kg and methylprednisolone 30 mg/kg/day were administered over the course of 5 days. Over the subsequent 6 days, he demonstrated marked improvement in language, behavior, appetite, and sleep. He was able to walk without support, and choreoathetoid movements diminished dramatically. Repeat cerebral and spine MR imaging remained normal.
At this time, results of CSF anti-NMDA-receptor antibodies were positive, and he was placed on mycophenolate with a plan to treat him with immune-modulatory therapy for a full year.