Post Herpetic Anti-NMDA- Receptor Encephalitis in an 18-month-old Infant.

Herpes simplex encephalitis (HSE), caused by herpes simplex virus type 1 (HSV-1), is the most common cause of severe sporadic encephalitis worldwide. HSE is occasionally accompanied by the recurrence of clinical symptoms that usually occur a few weeks following the initial infection. According to recent studies, the recurrence can be due to a secondary autoimmune mechanism rather than the virus invasion. One of the most common etiologies for autoimmunity is Anti-N-Methyl-D-Aspartate receptor encephalitis. This disorder is a treatable autoimmune encephalitis manifesting as movement disorder or neuropsychological involvement.

Case presentation: The article pertains to the presentation of an 18-month-old infant with a primary diagnosis of herpetic encephalitis who was re-admitted to the hospital shortly after discharge with restlessness, speech disorder, and abnormal movements. The movements were predominantly choreiform and disappeared during sleep. Brain MRI revealed abnormal predominance in the left temporoparietal regions with encephalomalacic changes in some areas in favor of sequella of previous encephalitis in addition to recent right temporal involvement of sequella of previous encephalitis. The polymerase chain reaction test of cerebrospinal fluid for herpes simplex infection was negative. Therefore, the possibility of autoimmune encephalitis was raised. More laboratory examinations revealed that the Anti-N-Methyl-D-Aspartate receptor antibody level was significantly elevated in cerebrospinal fluid. Thus, the diagnosis of Anti-N-Methyl-D-Aspartate receptor encephalitis was established.

Conclusion: Relapsing symptoms after herpes simplex virus encephalitis, especially with movement disorders, should raise a high clinical suspicion of Anti-N-Methyl-D-Aspartate receptor encephalitis in children. Therefore, clinicians should be cautious of its occurrence in infants; despite its rarity in that age group.