A 21-year-old-woman with no relevant medical history presented with a 1-week history of sore throat, fever and itchy rash. The examination revealed erythema in the oropharynx and vesiculopustular exudative lesions 2–3 cm in diameter over the face and erythematous vesicular “target” lesions in the trunk, upper limbs and the back of both hands (Fig. 1a–c). Laboratory tests, with the exception of the C-reactive protein level (4 mg/dL), were all normal. Blood cultures and cultures from skin lesions (for both virus and bacteria) were negative. However, the serological test for Mycoplasma pneumoniae (IgM; microparticle agglutination assay) was positive. Treatment with intravenous levofloxacin and topical mupirocin was initiated and the skin lesions gradually improved and the fever disappeared. A biopsy of the lesions was not performed given the improvement of the patient with the treatment administered and the positivity of the serology. However, a second blood sample was obtained 10 days afer the first serology result, observing a four-fold increase in IgM titre and, thus, the diagnosis of erythema multiforme (EM) secondary to M. pneumoniae infection could be made.

Fig. 1
figure 1

Vesiculopustular exudative lesions over the face and vesicular “target” lesions in the neck and the hands highly suggestive of erythema multiforme

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M. pneumoniae can cause skin lesions in up to 25 % of patients with pulmonary infections [1]. A non-specific exanthem is the most common cutaneous reaction related to M. pneumoniae, but other skin conditions, such as pityriasis rosea, Kawasaki disease, leukocytoclastic vasculitis, subcorneal pustular dermatosis, Sweet syndrome, toxic epidermal necrolysis, Henoch–Schönlein purpura and EM have been previously described [2]. However, the aetiologies of EM are commonly drugs (antibiotics, anticonvulsants) and infections (herpes simplex virus mainly). Since M. pneumoniae is a frequent cause of respiratory tract infection, being aware of potential mucocutaneous manifestations in these patients is advisable to any physician. On the other hand, patients presenting with EM should be evaluated for, but not only, herpes simplex virus, since many others infectious agents, such as M. pneumoniae, may produce it.