Severe Acute Meningoencephalitis Associated with Mycoplasma pneumoniae Infection in a Young Adult Successfully Treated with Immunotherapy.

A previously healthy 23-year-old man developed acute-onset fever, headache, and a rapidly deteriorating altered mental status, occurring 11 days after the resolution of self-limiting respiratory symptoms. The cerebrospinal fluid and brain MRI findings were consistent with meningoencephalitis. A recent M. pneumoniae infection was confirmed using nasopharyngeal PCR and serological testing. Despite appropriate antimicrobial therapy, his neurological deterioration progressed. The addition of steroids and intravenous immunoglobulin resulted in a rapid and complete neurological recovery. This case underscores the immune-mediated pathogenesis of M. pneumoniae-associated meningoencephalitis, particularly in cases with a delayed neurological onset following respiratory prodromes. Clinicians should therefore consider early immunotherapy in conjunction with antibiotics, even in adult populations.