A Prospective and Retrospective Analytic Study of Infectious Cause of Encephalitis in Thailand
Authors:   , Skulsujirapa Benjawan 
Published: November 2023

Background: Previous reports of infectious encephalitis in Thailand showed viruses as major pathogens similar to worldwide data. Major viruses in studies varied among Japanese encephalitis, enteroviruses and herpesviruses.  Infectious etiologies vary by regions, seasons and preventive strategies done. Dynamic change of pathogen is believed to occur continually. Local data in each region is important to develop an algorithm of investigations for the cost-effectiveness.

Objectives: To study the etiology of encephalitis in a tertiary-care hospital using extensive tests Methods: This is a prospective study of patients with encephalitis between November 2016 to March 2017 and a retrospective review of the clinical data and prospective analysis of  archived samples of patients  with encephalitis who were admitted to the King Chulalongkorn Memorial hospital, a tertiary hospital in Bangkok, from January 2014 to October 2016. Microbiological and serological studies were done according to an algorithm based on initial cerebrospinal fluid analysis. Initial tests were for bacteria, fungus, mycobacterium and commonly prevalent viruses. In cases that initial results yielded negative findings, further testing for infectious etiology was done by stepwise approach. 9 family-wide  polymerase chain reaction  of viruses was performed to assess for infectious etiology. Results: Fifty-two patients were enrolled. Twenty-seven (51.9%) patients had no etiology identified. Three patients (5.8%) had bacterial etiology, 10 (19.2%) had viral etiology, and 12 (23%) had immune-mediated encephalitis. Varicella zoster virus was identified in 4 cases, HSV in 3 cases, CMV in 2 cases, measles in 1 case, L. monocytogenes in 2 cases and S. agalactiae in 1 case. No arbovirus nor emerging viral pathogens were identified. Six patients had anti-NMDA encephalitis, 3 cases had orobuccal dyskinesia, which was found only in anti-NMDA encephalitis in our study. Only 1 out of 6 patients was found to have teratoma. Baseline characteristic of HIV infection and the presence of skin rash were associated with viral etiology.  Patients with VZV encephalitis might not have active skin lesion at the onset of neurological symptoms.  Dysphasia was associated with infectious etiology, abnormal movement was associated with viral etiology and anti-NMDA encephalitis, motor weakness was associated with viral and unknown etiology. Cerebrospinal fluid profile of the immune-mediated encephalitis had the lowest number of white blood cells and protein. All patients survived at 7 days after admission. Conclusion:  Infection caused by herpesviruses was the most prevalent viral etiology, similar to studies from most developed countries. Emerging viral pathogens were not detected to cause encephalitis in this study.  A quarter of patients presenting with acute encephalitis in this study had immune-mediated encephalitis. Fewer ratio of anti-NMDA encephalitis patients with teratomas than in western case series.   Autoimmune and paraneoplastic encephalitis should be kept in the differential diagnosis in patients with acute encephalitis.