PO008 Extreme delta brush on eeg – secondary to ketamine use?

Background The extreme delta brush (EDB) pattern is considered pathognomonic of anti-NMDAR encephalitis. Ketamine, a NMDA receptor antagonist has induced a similar pattern on EEG when used as an anaesthetic or for refractory epilepsy. We present a case of EDB without a diagnosis of anti-NMDAR encephalitis but with possible ketamine use. Case An 18 year old male who regularly uses illicit drugs including cannabis and benzodiazepines, presented to hospital after a road traffic accident with aggression and agitation. He self-discharged and was found collapsed with severe hypoxia secondary to pneumonia. On ICU he developed stereotyped movements of the limbs with oral-facial movements. An EEG demonstrated global cortical dysfunction with an EDB pattern. He had bilateral acute pallidal and corona radiata signal change on MRI, suggestive of hypoxic injury. CSF was unremarkable. He was treated for presumed seizures but was not immunosuppressed. He subsequently improved and admitted to using ketamine infrequently. CSF and serum NMDA receptor antibodies were later confirmed as negative. Conclusions This is the second reported case of EDB without a diagnosis of anti-NMDAR encephalitis. The EDB could be explained by the suspected ketamine use, which may suggest it is specific for NMDA receptor blockade rather than encephalitis.