Evaluation of maculopapular rash

The patient with an acute maculopapular rash presents a diagnostic challenge to the clinician. The term "maculopapular" is nonspecific, as many eruptions have a primary morphology of macules or papules, and the term may be misused to indicate any rash. The term "rash" is also nonspecific and is sometimes incorrectly applied to any skin finding; eruption may be preferred for a cutaneous reaction of acute onset. However, the term "maculopapular rash" is in common clinical use and will be retained here for simplicity. Synonyms for maculopapular rash include exanthematous eruption (exanthem) and morbilliform eruption.

Definitions

The term maculopapular rash typically implies an acute and generalized eruption.

Morphologic terms

• Macule: a flat, circumscribed skin lesion ≤1 cm in greatest diameter. When macules are >1 cm, the appropriate term is patch.

• Papule: an elevated, circumscribed skin lesion ≤1 cm in diameter. When papules are >1 cm in size, the appropriate term is plaque (palpable lesions elevated above the skin surface) or nodule (a larger, firm papule with a significant vertical dimension).

Other morphologic terms encountered in this clinical setting include:

• Pustule: a papule containing purulent fluid

• Vesicle: a papule containing clear serous fluid

• Bulla: a larger vesicle >1 cm

• Urticaria: a wheal or hive.

The term maculopapular rash, therefore, implies a skin eruption of flat and raised lesions.