Introduction: Early electroencephalogram (EEG) revealing extreme delta-brush,¹ and other focal and unilateral electro-clinical features² have been reported in N-Methyl-D-Aspartate receptor (NMDAR) antibody encephalitis. We evaluated the electrophysiological features of children with a range of autoimmune encephalitides, to identify similar and other features.   

Methods: 34 consecutive patients (identified from cohort of 40) with presumed autoimmune encephalitis as previously defined³ with acute and/or follow-up EEG recordings available for blinded review by a paediatric neurophysiologist, were studied. 

Results: 6 NMDAR antibody positive patients with focal or multifocal seizures had EEG demonstrating either diffuse slowing with spike wave discharges (n=1), unilateral hemispheric slowing (n=3) or focal slowing (n=2). 4/6 voltage-gated potassium channel (VGKC) antibody positive patients had focal temporal slowing with 3 having additional diffuse changes, of which 2 had ictal activity. In the remaining antibody positive group (n=4; glycine receptor, thyroid, basal ganglia, ganglioside); and negative group (n=18), EEG features ranged from normal (n=4), focal slowing (n=6), diffuse slowing (n=11) and PLEDS (n=1), with ictal activity observed in 7. Overall, the antibody positive group were more likely to have persistingly abnormal EEG (7/12 vs 7/22); and these changes were also abnormal for longer ( mean 12 vs 6 months).

Conclusion: Previously reported EEG features of NMDAR antibody encephalitis were identified in our patients. Other than the unilateral hemispheric slowing, the other features identified in patients with autoimmune encephalitis were shared across the antibody positive and negative group.