Clinical characteristics of possible Mycoplasma pneumoniae-associated meningoencephalitis in adults.

OBJECTIVES: To characterize clinical profiles of adults with possible Mycoplasma pneumoniae-associated meningoencephalitis and evaluate whether serologic diagnostic categories are associated with phenotypes or prognosis. METHODS: We conducted a retrospective, single-center cohort study (March 2005-July 2023). Among 184 adults with meningoencephalitis who underwent confirmatory testing for M. pneumoniae, 39 met predefined criteria for possible M. pneumoniae-associated meningoencephalitis based on serologic evidence and were stratified into seroconversion (n = 8), IgM-positive (n = 11), and single high-titer (≥1:320; n = 20) subgroups. RESULTS: Median age was 40 years (IQR, 30.5-49) and differed across subgroups (P = 0.018). Cerebrospinal fluid (CSF) leukocyte counts were higher in the IgM-positive group (P = 0.031), while other CSF parameters were similar. Brain MRI abnormalities were common (78.9%), with leptomeningeal enhancement in 55.3%. EEG abnormalities were found in 35.9%, most often diffuse cerebral dysfunction. Median hospitalization was 15 days; 76.9% received targeted antibiotics (median 7 days). Ninety-day mortality was 2.6% (unrelated to meningoencephalitis), and neurologic sequelae occurred in 28.2%. CONCLUSIONS: In adults with possible M. pneumoniae-associated meningoencephalitis, we observed an intermediate inflammatory and imaging phenotype between classic bacterial and viral central nervous system (CNS) infections. Despite low mortality, neurologic sequelae were frequent. Serologic subgroups were associated with differences in inflammatory profiles and treatment patterns but not major clinical outcomes.