Background: Primary EBV infection is usually asymptomatic or manifests as infectious mononucleosis with fever, lymphadenopathy, and tonsillitis. It is an uncommon cause of clinically significant central nervous system infection in adolescents and can present with altered sensorium and seizures. Around 5 % of viral encephalitis are due to EBV infection. Direct viral invasion and a secondary autoimmune response directed against the brain is thought to cause symptoms and imaging findings.Case description:“He had a positive mono test”.That was the opening line when we saw the 14-year-old boy return to our ED. Just the day before, he’d been discharged with what seemed to be a straightforward case of infectious mononucleosis. Fever, sore throat, fatigue, a positive mono-spot Test—he ticked all the boxes. Blood investigations supported the viral picture. Nothing appeared out of the ordinary. But less than 24 hours later, he was back—and everything had changed. That evening, he had a brief seizure at home, fluctuating level of consciousness, followed by status epilepticus. He was treated initially in our resuscitation department with fluid boluses, antimicrobial, antivirals and antiepileptic medication followed by transfer to PICU CHI and subsequent improvement and resolution of encephalopathy both clinically and radiologically and discharged home on per oral course of valacyclovir.Investigations: Positive mono-spot test, positive EBV serology both IgM and IgG but negative CSF PCR for EBV. MRI findings of bilateral and symmetrical T2 FLAIR hyper intensities of caudate and putamen nuclei, with no evidence of diffusion restriction or lactate peak, possibly consistent with EBV encephalitis.Conclusion: This case reminded us that even so called “simple” viral illnesses can turn into complex without warning. That our certainty—however well-grounded—should always leave space for humility and reassessments. It is not just to treat what we see—but to anticipate what might be coming next.
