Use of Ketamine Needs Caution in NMDA-R Encephalitis Related Status Epilepticus

Anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis is characterised by the antibodies decreasing the NMDAR surface density and synaptic localization by selective antibody-mediated capping and internalization of surface NMDAR. Ketamine is a NMDAR antagonist which can produce dose-dependent, self-limiting side effects such as hypersalivation, hyperreflexia, transient clonus, dizziness, nausea, vomiting, tachycardia, hypertension, and detrusor muscle overactivity. A 22-year-old girl presented with recent onset behavioral change, progressive movement disorder and later lapsed into super refractory status epilepticus (SRSE). She was treated with at least four antiseizure medications, immunomodulation as well as anesthetic drugs with only partial relief in status. Ketamine was added for SRSE and led to a significant worsening of clinical symptoms with abatement after stopping. She finally responded to thiopentone infusion. Ketamine has been found to be beneficial in SRSE in encephalitis including anti-NMDAR encephalitis. This is seemingly counterintuitive given how the action of the drug mimics the pathophysiology of the disease. This report highlights the risk of paroxysmal sympathetic hyperactivity and aggravation of clinical and electrographic features of anti-NMDAR encephalitis with ketamine. Hence, ketamine and similar medications acting on the NMDAR should be used with caution in anti-NMDAR encephalitis.