Objective:

To evaluate the results of follow-up lumbar punctures (LP) and characteristics of encephalitis patients undergoing repeat LPs.  

Background:

Clinical case definitions often rely on cerebrospinal fluid (CSF) results to indicate central nervous system inflammation in encephalitis, though some patients present with subtle signs of inflammation on initial LP. This study examines temporal changes in CSF results and explores the rationale behind repeating LP, aiming to identify patterns that improve diagnosis and care in encephalitis cases. 

Design/Methods:

This retrospective study analyzes LP data from the initial hospital admissions of 627 adult encephalitis patients, including autoimmune and infectious cases, from 2002 to 2022.  

Results:

Of 627 patients, 184 (29.3%) underwent follow-up LPs. Inflammatory markers, such as white blood cell (WBC) count, significantly decreased on repeat LP (median WBC LP1 = 38 vs. LP2 = 19, p < 0.001), with the decline becoming apparent three days after the initial LP. Patients with repeat LPs were more likely to have autoimmune encephalitis (22%) compared to those with a single LP (16%), p=0.04. Conversely, patients with a single LP were more frequently diagnosed with infectious encephalitis (48.1%) than those undergoing repeat LPs (33.7%), p<0.001. Patients with more severe clinical presentations (e.g., status epilepticus, altered mental status) and hospitalization course (e.g., prolonged admission, lower GOS score, ICU admission) were significantly more likely to undergo repeat LPs. Diagnostic uncertainty and lack of response to treatment were common reasons for repeat LPs. Notably, 93.2% of patients with a definitive diagnosis had positive findings on the initial LP, while subsequent LPs rarely provided new diagnostic information.  

Conclusions:

Our study found that repeat LPs were more common in autoimmune and severe encephalitis cases but rarely provided additional diagnostic insights. This emphasizes the importance of the initial LP.