Discussion
In the autumn of 2024, a large outbreak of M. pneumoniae was observed in Norway, primarily affecting children and adolescents (1). Such infections can lead to various complications, and extrapulmonary manifestations, such as cutaneous and mucosal symptoms, arthritis, haemolytic anaemia and pericarditis, occur in approximately 25 % of cases (2). Cutaneous and mucosal manifestations of M. pneumoniae infection have previously been considered variants of erythema multiforme or Stevens–Johnson syndrome, which remain the two main differential diagnoses.
The term Mycoplasma pneumoniae-induced rash and mucositis was proposed in 2015 as a distinct disease entity, separate from erythema multiforme and Stevens–Johnson syndrome (3). In recent years, the broader and less specific designation 'reactive infectious mucocutaneous eruption' has gained acceptance, encompassing similar cutaneous and mucosal symptoms triggered by other infectious agents, including several viral pathogens (4). Mycoplasma pneumoniae-induced rash and mucositis, however, is specifically associated with M. pneumoniae and occurs simultaneously with, or approximately one week after, the onset of respiratory symptoms, suggesting a direct immune response to the infection (3). Proposed pathophysiological mechanisms include tissue injury followed by the release of inflammatory cytokines and deposition of immune complexes with accompanying complement activation (4). The condition is characterised by marked mucosal involvement at a minimum of two sites: oral, ocular and/or genital mucosa, with painful ulcerations. Cutaneous rash is not obligatory, and when present, is often less prominent and nonspecific (frequently vesiculobullous) (3). The condition predominantly affects boys, with a median age of 12 years (4).
Erythema multiforme is a delayed hypersensitivity reaction, typically following herpes simplex virus infection in adults aged 20–40 years (5), but it can also be triggered by M. pneumoniae, particularly in children (6). The rash is variable, but typically affects the distal extremities and is characterised by classic target lesions. Stevens–Johnson syndrome is an acute, life-threatening cutaneous disorder, characterised by fever, rash and mucosal involvement. It is almost always drug-induced, with mortality up to 25 %, and can occur at any age (7).
Both Mycoplasma pneumoniae-induced rash and mucositis and erythema multiforme are managed by addressing the underlying trigger, with antibiotic or antiviral therapy as appropriate. Ocular involvement should be assessed early, as scarring can lead to sequelae (8). In cases of extensive mucosal involvement, immunosuppressive therapy with systemic corticosteroids is often administered; however, studies of erythema multiforme suggest minimal benefit and, in the worst case, a potential for prolonged or chronic disease (3, 5, 9). No studies have evaluated the efficacy of immunosuppression in Mycoplasma pneumoniae-induced rash and mucositis (3), although case reports describe potentially faster recovery (4, 10). Our patient received high-dose systemic corticosteroids with apparent clinical benefit and no complications. Nevertheless, we emphasise that there is insufficient evidence regarding optimal corticosteroid dosing or the role of such treatment given the generally benign course of the condition.
M. pneumoniae has a tendency to cause epidemics, and several cases of reactive mucocutaneous eruptions have been reported in association with such infections. Internationally, both terms – Mycoplasma pneumoniae-induced rash and mucositis (MIRM) and reactive infectious mucocutaneous eruption (RIME) – are used, and both are referenced in recent textbooks and knowledge bases. Which term will ultimately become standard remains uncertain. In clinical practice, however, it is crucial to recognise that patients with bacterial or viral respiratory infections may develop mucosal involvement with or without a rash, and to differentiate between a reactive infection-triggered condition and a drug-induced reaction, as management strategies and prognosis differ substantially.