Dx: Mycoplasma pneumoniae–induced rash and mucositis
Further follow-up on Day 6 of illness revealed bibasilar crepitations along with an elevated CRP level of 40.5 mg/L and a positive mycoplasma antibody serology (titer > 1:1280; normal, < 1:80). The patient was given a diagnosis of pneumonia (due to infection with Mycoplasma pneumoniae) and M pneumoniae–induced rash and mucositis (MIRM).
MIRM was first proposed as a distinct clinical entity in 2015 to distinguish it from Stevens-Johnson syndrome and erythema multiforme.1 MIRM is seen more commonly in children and young adults, with a male preponderance.1
A small longitudinal study found that approximately 22.7% of children who have M pneumoniae infections present with mucocutaneous lesions, and of those cases, 6.8% are MIRM.2 Chlamydia pneumoniae is another potential causal organism of mucositis resembling MIRM.3
Pathogenesis. The commonly accepted mechanism of MIRM is an immune response triggered by a distant infection. This leads to tissue damage via polyclonal B cell proliferation and subsequent immune complex deposition, complement activation, and cytokine overproduction. Molecular mimicry between M pneumoniae P1-adhesion molecules and keratinocyte antigens may also contribute to this pathway.
3 criteria to make the diagnosis
Canavan et al1 have proposed the following criteria for the diagnosis of MIRM:
- Clinical symptoms, such as fever and cough, and laboratory findings of M pneumoniae infection (elevated M pneumoniae immunoglobulin M antibodies, positive cultures or PCR for M pneumoniae from oropharyngeal samples or bullae, and/or serial cold agglutinins) AND
- a rash to the mucosa that usually affects ≥ 2 sites (although rare cases may have fewer than 2 mucosal sites involved) AND
- skin detachment of less than 10% of the body surface area.
Continue to: The 3 variants of MIRM include...