To compare incidence, demographics, and clinical outcomes in U.S. patients with diagnosis of unspecified cause of encephalitis stratified by type of immune therapy, plasma exchange (PLEX) vs. intravenous immunoglobulin (IVIG). 

Encephalitis can be an incapacitating disorder secondary to inflammation of brain parenchyma. The ability to detect specific antibodies in CSF and serum has increased recognition of non-infectious etiologies such as autoimmune encephalitis. The morbidity and mortality with untreated disease demonstrates the need for disease awareness and prompt treatment.

We conducted a retrospective case control study using the Healthcare Cost and Utilization Project - National Inpatient Sample database for years 2005 to 2014. Our cohort included the diagnosis ICD-9 code 323.9, Unspecified Cause of Encephalitis. Within this cohort, the ICD-9 procedure code for IVIG (99.14) and PLEX (99.71) was used to identify patients who received these treatments during their hospital stay.  Multivariate regression analyses were utilized to analyze data.

A total of 15,605 patients with diagnosis of unspecified cause of encephalitis were found. Among those, 159 and 188 patients received IVIG and PLEX, respectively. The cohort treated with IVIG was mostly male (51.6%), white (60.7%) with mean age of 34. The cohort treated with PLEX was mostly female (59.6%), white (58%) with mean age of 44.3. Mean length of stay was longer for cohort treated with PLEX at 31.1 days vs. 22.9 days for IVIG. Both cohorts (IVIG vs. PLEX) had private payers (48.7% and 57.8%), and were hospitalized in academic centers (89.2% and 86.7%). PLEX treated cohort was 37% (p<0.01) less likely to be discharged to home, and 79.6% (p<0.01) more likely to be transferred to another facility. 

We found immunotherapy has been increasingly used in diagnoses of unspecified cause of encephalitis. Our findings provide a picture of the outcomes and the type of patients treated for suspected autoimmune encephalitis.