Functional outcome after infectious encephalitis: a longitudinal multicentre prospective cohort study

Objectives: We aimed to describe longitudinal functional outcome among survivors after an infectious encephalitis (IE) and to analyse risk factors for poor functional outcome.

Methods: Patients included in the prospective ENCEIF cohort (France, 2016-2019) were followed-up at 6 months and 1 year after hospital discharge for assessment of (a) functional outcome using modified Rankin scale (mRS) and (b) cognitive function and abilities to perform activities of daily living. Risk factors for poor outcome on the full distribution of mRS were estimated using multivariable mixed ordinal regression analysis with time between hospital discharge and follow-up as a covariate.

Results: Our follow-up study included 322 patients with 896 mRS evaluations. Median age was 66 (50-74) years, 197/322 were male (61%) and 35/322 were immunocompromised (11%). Causative agents were herpes simplex virus 1 in 95/322 cases (30%), varicella zoster virus in 46/322 cases (14%), others documented IE in 90/322 cases (28%) and unknown in 91/322 cases (28%). Intensive care unit (ICU) admission was necessary for 117/322 patients (36%). Brain imaging was abnormal in 180/311 (58%) of patients. At 6 months, 95/287 (33%) had fully recovered and 181/287 (63%) had persisting symptoms. At 12 months, 124/253 (49%) had fully recovered and 108/253 (43%) had persisting symptoms. The proportion of patients who improved was 41% (117/287) during the first 6 months, and 24% (52/218) between 6 and 12 months. Factors significantly associated with poor functional outcome were age, immunosuppression, ICU admission, abnormal brain imaging and causative agents, notably herpes simplex virus 1. Follow-up visit during the first 120 days did not detect significant change in functional outcome, but was strongly associated with better outcome at the subsequent evaluation.

Discussion: After IE, improvement may take several months. Functional outcome is associated with baseline health status (age and immunosuppression), abnormal brain imaging, ICU admission and causative agents.