Aim We present an atypical case of NMDAR Ab Encephalitis (N-methyl-D-Aspartate Receptor Antibody Encephalitis) with recurrent right sided focal seizures, right hemiparesis and hemiplegia. The youngest case in UK to be described without significant psychiatric component.

Methods 4 years 10 month old girl born in UK to Zimbabwean Parents. She had been well with not relevant family history. She presented with right sided focal seizure and reduced movement. She had 2 episodes of generalised tonic convulsions involving the right side associated with loss of consciousness which lasted for 2 min and then 10 min; 5 min apart. The seizures was managed with diazepam. No preceding trauma, fever, neck pain, headache or vomiting. Her right sided weakness which improved within 2 h.

She was then re admitted 4 days later with right focal seizure with persisting right sided weakness, dysarthria and right sided facial palsy. She had amnesia without any new psychotic features

Baseline blood and CSF Investigation were normal. Lyme serology, ASOT, Lupus screen, all viral PCR and throat swab were negative. ECG, Echo and EEG was normal. CSF amino acid, ammonia, Lyme titre, oligoclonal bands, mitochondrial DNA, acylcarnitine profile was normal. MRI showed possible left MCA infarct with a picture of encephalitis with oedema.

She was treated with antibiotics, lorazepam, Aspirin and Omeprazole. Repeat MRI ruled out a stroke so Aspirin was stopped and started on IV methylprednisolone.

Repeated MRI brain suggested an inflammatory process with evidence of maturing damage suggestive of neurometabolic or neuroinflammatory disorder. Importantly the CSF and blood NMDAR antibody returned positive with rising titres of blood NMDAR ab.

Results NMDA Receptor Antibody Encephalitis was diagnosed and treated with Prednisolone 30 mg OD for 8/52, advised avoiding live vaccines and IVIG 1 g/kg for 2/7. MMF 200 mg BD planned for 18–24 months- dose to be adjusted based on response. Monthly NMDAR ab blood and CSF have been positive for 10 months after diagnosis. She is on Annual surveillance for tumours with MRI or USS. She continues to have physiotherapy and Neuropsychology input.

Conclusion Atypical focal seizures may need further evaluation and NMDAR ab considered with atypical presentations resulting in better outcome.