There are many types of maculopapular exanthema which require an excellent knowledge of nosology and a great experience in order to make a diagnosis. It is essential to perform an in-depth analysis of the associated signs (forewarning signs, influenza-like symptoms, enlarged lymph nodes, enanthema), of the comorbidity, and a drug history. As such, exanthema from measles is maculopapular and confluent while leaving intervals of unaffected skin. It starts from behind the ears and shows a downward progression in a child or adult affected by an oculonasal catarrh, with alteration of the general condition. Its primary lesion is a folliculitis or a perifollicular erythema. The presence of a characteristic associated enanthema (Koplik’s sign) enables diagnosis. The exanthema from Still’s disease is transient and consists of macules and pink plaques that are barely palpable and ­particularly located on the trunk. It occurs in the late ­afternoon during febrile peaks. The ­associated signs, joint pains, cervical adenopathy, pharyngitis, inflammatory syndrome, leukocytosis, and hepatitis, hold a high diagnostic value.

While drug-induced exanthemas can be pruritic, most infectious exanthemas are not. A confluent erythema, localized or generalized, with edema of the extremities and a marked enanthema, is common in superantigen diseases such as scarlet fever, staphylococcal toxic shock syndrome, or Kawasaki disease. The onset of Lyell’s syndrome must be feared in the presence of a macular exanthema evolving towards skin detachment that requires to be thoroughly searched by traction of the skin.

For teaching purposes and in spite of the great value of the nature of the primary lesion, papular and vesicular exanthema are also addressed in this chapter, because they represent a true differential diagnosis on account of their eruptive nature.