The challenge of diagnosing atypical exanthems: a clinico-laboratory study

Although atypical exanthems pose a severe diagnostic challenge, they have not been studied widely.

To identify the clinical features, laboratory parameters and other characteristics that help establish the etiology of atypical exanthems.

We collected the following information from 260 consecutive patients with atypical exanthems, including 108 children and 152 adults: demographic data, exanthem and enanthem morphology, clinical symptoms, month of outbreak and total duration. Throat, rectal, and vesicle swabs as well as urine and skin samples were examined for bacterial and viral signs. Serologic studies were performed for the most common infectious agents.

Seven morphological patterns were identified: macular erythema, papular erythema, macular-papular erythema, erythematovesicular, macular-papular erythema with petechiae, erythema with pustules, and urticarial. Ninety-four cases were due to viruses, 38 to bacteria, 65 to drugs, 3 to parasites, and one to viruses-plus-drugs. Nineteen of the 25 cases with a petechial pattern had an infectious etiology (12 viral and 7 bacterial) and only 4 were iatrogenic. Sixty-one of 69 patients with enanthems were infectious (57 viral and 4 bacterial), 6 were iatrogenic, and 2 remained undiagnosed. The petechial pattern was infectious in 80% of cases (14 viral and 2 bacterial). Four cases were iatrogenic. During the spring and summer, 60% of exanthems were infectious and 21% were iatrogenic. Picornavirus infections exhibited summer prevalence (57%), peaking in July.

There were a variable number of patients with each of the morphological patterns.

Morphological patterns, seasonal occurrence, and enanthem are key for etiological diagnosis of atypical exanthems.