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Mycoplasma pneumoniae may cause encephalitis with a wide range of clinical manifestations in the pediatric population, with or without inoculation of cerebral spinal fluid (Christie et al., 2007). We report a case of a child presenting with fever and encephalopathy who was found to be seropositive for M. pneumoniae and myelin oligodendrocyte glycoprotein (MOG) antibodies.

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A 10-year old previously healthy male presented to the emergency department with 10 days of fever, cough, and lethargy. He showed initial improvement on doxycycline. Brain and spine magnetic resonance imaging (MRI) were unremarkable. Seven days into his hospital course, he had increased confusion, fever, and seizure-like episodes. Serum M. pneumoniae IgG and IgM were elevated. Treatment with azithromycin, doxycycline, and intravenous immunoglobulin (IVIG) was initiated. Subsequently, anti-MOG antibodies were found to be positive. The patient gradually improved and was discharged home 6 days later with outpatient follow up with neuroimmunology.

In uncomplicated cases of M. pneumoniae encephalitis, treatment with an intravenous antibiotic regimen alone may be sufficient (Meyer et al., 2011). However, patients who receive azithromycin plus IVIG may also have improved outcomes and quicker recovery (Fan et al., 2023). Our patient was found to be positive for anti-MOG antibodies despite having no evidence of demyelination on imaging. In these cases, treatment with immunomodulatory therapy is indicated and effective in agreement with what has been recorded in other cases of MOG-positive encephalitis (Huang et al., 2023).

This case represents a complex manifestation of M. pneumoniae encephalitis with positive anti-MOG antibodies without demyelination on MRI. Seropositivity for autoimmune markers may suggest a longer clinical course and recovery time with increased risk of relapse. Treatment with antibiotics alone is not sufficient for cases of M. pneumoniae encephalitis with autoimmune involvement, and providers should not exclude immunomodulatory therapy even in the absence of demyelination.