# From Respiratory Pathogen to Systemic Threat: Rethinking Mycoplasma pneumoniae Infections

## TL;DR

Mycoplasma pneumoniae, once seen as a lung infection, can cause serious problems in multiple body systems, requiring a new approach to diagnosis and treatment.

## Contribution

The paper proposes a paradigm shift in viewing M. pneumoniae as a systemic pathogen rather than a respiratory one.

## Key findings

- M. pneumoniae can cause neurological, cardiac, and other systemic complications through direct invasion or immune mechanisms.
- Diagnosis is challenging due to delayed serology and lack of pathogen detection in sterile sites.
- Management requires antimicrobial therapy, supportive care, and immunomodulation for severe cases.

## Abstract

Mycoplasma pneumoniae is traditionally recognized as a leading cause of community-acquired pneumonia, yet growing evidence demonstrates that its clinical impact extends far beyond the respiratory tract. Increasing reports of neurologic, cardiac, hematologic, dermatologic, renal, gastrointestinal, and thrombotic complications indicate that M. pneumoniae should be viewed as a systemic pathogen capable of inducing multisystem disease. Extrapulmonary manifestations may arise through three major mechanisms: direct bacterial invasion of tissues, immune-mediated injury driven by molecular mimicry or immune complexes, and vascular or thrombotic events related to endothelial dysfunction. These processes frequently occur independently of, or temporally dissociated from, respiratory symptoms, complicating early diagnosis. The diagnostic approach remains challenging because respiratory PCR may reflect colonization, serology is delayed, and pathogen detection in sterile sites is uncommon. Consequently, diagnosis often depends on the integration of clinical features, laboratory markers, and organ-specific imaging. Management requires a combined strategy: antimicrobial therapy to reduce bacterial load, organ-targeted supportive measures, and immunomodulatory interventions such as corticosteroids, IVIG, or plasma exchange for severe immune-mediated complications. The emergence of macrolide-resistant strains further underscores the need for tailored antimicrobial strategies and close clinical monitoring. Although many extrapulmonary complications are reversible, severe forms—including encephalitis, ADEM, myocarditis, Stevens–Johnson syndrome, and major thromboses—can lead to lasting morbidity or death. Significant knowledge gaps persist, including determinants of host susceptibility, mechanisms linking CARDS toxin to systemic inflammation, the impact of macrolide resistance on disease severity, and the absence of standardized diagnostic criteria. Advances in molecular immunology, multicenter registries, and development of targeted therapies or vaccines represent crucial next steps. Overall, the breadth and clinical relevance of extrapulmonary involvement support a paradigm shift: Mycoplasma pneumoniae infection should be regarded and managed as a systemic disease rather than a purely respiratory pathogen.