A Rare Case of Adult-Onset Human Parechovirus Type A3 Encephalitis.

Adult-onset human parechovirus (HPeV) encephalitis is extremely rare. We report the first case of HPeV encephalitis in Japan in an 82-year-old man with diabetes, who presented with an impaired consciousness and status epilepticus (SE). A cerebrospinal fluid (CSF) analysis revealed a normal cell count with elevated protein levels. Magnetic resonance imaging showed hyperintense signals in the thalamus and parietal lobe, and HPeV type 3 was detected in the CSF. SE resolved following antiepileptic treatment, and the patient's cognitive function recovered. Adult HPeV encephalitis may present with SE, an absence of pleocytosis, and "reversible" cognitive deficits, highlighting the diagnostic utility of multiplex polymerase chain reaction testing in encephalitis without pleocytosis.