Objective:

Investigating the epidemiology and clinical characteristics of encephalitis cases in a large tertiary center.

Background:

The incidence of autoimmune encephalitis has risen in the last decade. Studies
regarding its incidence are lacking.

Design/Methods:

We reviewed the Tel-Aviv Medical Center database to identify all patients > 18
years that were hospitalized with Infectious or autoimmune encephalitis (IE or AIE), in
order to compare their incidence and characteristics.

Results:

Between 2010 and 2020 a total of 225 patients with encephalitis were
identified. The most common identifiable cause was viral (42%), followed
by AIE (35%), bacterial (18%), and fungal/parasitic (~5%).
The incidence of AIE cases out of the yearly admitted cases, more than quadrupled
between 2010 and 2020. The incidence of viral cases showed a similar substantial
increase, while the rates of bacterial and fungal/parasitic infections remained stable.
Patients with AIE presented at a younger age compared to infectious patients (p-value
<0.001), and with significantly lower markers of systemic inflammation, as well as
reduced CSF inflammatory markers (p-value for all <0.001). Seizures were
more common among AIE patients (p value=0.0006), yet one-year mortality
was significantly higher among infectious patients (p-value<0.001).

Conclusions:

The incidence of AIE in our institution has significantly increased during the past
decade, most recently displaying rates comparable to those of all infectious causes
combined. This shift may be attributed to discoveries of novel clinical syndromes and
improved diagnostic methods; to increasing awareness of AIE; and to the opening of
an AIE clinic in our center in 2017. Based on our cohort, clinical clues that should
raise suspicion of AIE in a patient with encephalitis include: a
non-inflammatory CSF profile, seizures, and temporal lobe imaging
abnormalities (also common in HSV1 encephalitis). AIE should be
high in the differential diagnosis in encephalitis cases, due to its comparable
incidence to IE and the importance of early treatment.