Background: Cytotoxic lesions of the corpus callosum (CLOCCs) are classically associated with benign viral infections; however, bacteria-induced CLOCCs frequently exhibit more aggressive clinical phenotypes. Concurrent central nervous system (CNS) infections by Streptococcus pneumoniae (SP) and Mycoplasma pneumoniae (MP) are exceptionally rare, and their synergistic pathogenesis remains poorly understood. Case Presentation: We report a 9-year-old boy presenting with severe encephalopathy (GCS 8), purulent cerebrospinal fluid (CSF), and profound localized cytokine elevation (CSF IL-6 >50,000 pg/mL), accompanied by an isolated splenial MRI lesion. Initially, false-negative MP-PCR results risked early diagnostic anchoring, resulting in targeted therapy exclusively for SP meningitis. This unmasked a classic biphasic clinical course, characterized by a secondary high fever and severe agranulocytosis on day 17. The underlying MP-driven immune response was subsequently confirmed via serology and successfully treated with macrolides and high-dose corticosteroids, leading to full neurological recovery. Conclusions: SP and MP co-infections underscore the complexity of dual-pathogen CNS involvement. The risk of diagnostic anchoring and biphasic clinical evolutions necessitates high vigilance. Timely integration of comprehensive molecular diagnostics and potent immunomodulation is paramount for optimizing outcomes in these rare, life-
Yilun Tao (Thu,) studied this question.