Mildly pruritic palmar rash
After taking azithromycin and prednisone for lower respiratory symptoms, this patient developed a rash. The way it spread provided a diagnostic clue.
Diagnosis: Erythema multiforme
The clinical exam was consistent with the diagnosis of erythema multiforme (EM). A diagnosis of EM can usually be made based on the clinical exam alone.1 Typical targetoid lesions have a round shape and 3 concentric zones: A central dusky area of epidermal necrosis that may involve bullae, a paler pink or edematous zone, and a peripheral erythematous ring.2 Atypical lesions, such as raised papules, may also be seen.2
The skin lesions of EM usually appear symmetrically on the distal extremities and spread in a centripetal manner.1 Palms, soles, and mucosa can be involved.1 EM with mucosal involvement is called “erythema multiforme major,” and EM without mucosal disease (as in our patient’s case) is called “erythema multiforme minor.”2
EM is an acute, immune-mediated eruption thought to be caused by a cell-mediated hypersensitivity to certain infections or drugs.2 Ninety percent of cases are associated with an infection; herpes simplex virus (HSV) is the most common infectious agent.3 Mycoplasma pneumoniae is another culprit, especially in children. Medications are inciting factors about 10% of the time; nonsteroidal anti-inflammatory drugs, sulfonamides, antiepileptics, and antibiotics have been linked to EM eruptions.3
,Interestingly, while azithromycin—the medication our patient had taken most recently—can cause EM, it has been mainly linked to cases of Stevens-Johnson syndrome (SJS).4 So, while we suspect that azithromycin was the trigger in our patient’s case, we can’t be sure. It’s also possible that Mycoplasma pneumoniae was the trigger for our patient’s EM. However, Mycoplasma pneumoniae is more common in adolescents.
Differential includes life-threatening conditions like SJS
The differential diagnosis for a non-vesicular palmar rash is discussed in the TABLE.1,5-12 There is a wide spectrum of possible etiologies—from infectious and rheumatologic disorders to chronic liver disease. Histologic testing may be useful in differentiating EM from other diseases, but in most cases, it is not required to make a diagnosis.1 Laboratory testing may reveal leukocytosis, an elevated erythrocyte sedimentation rate, and elevated liver function test results, but these are nonspecific.1
