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  1. Problem. A nurse calls you to tell you that an infant has a rash and wants you to evaluate it. A rash is any change of skin that affects its color, appearance, or texture. Although the majority of rashes in newborns are benign and require no treatment, certain rashes require a workup and intervention.

  2. Immediate questions

      1. What are the characteristics of the rash? Morphology of the lesion aids differential diagnosis. Is it macular (flat lesion <1 cm), papular (raised up to 1 cm), nodular (raised up to 2 cm), vesicular (raised, <1 cm, filled with clear fluid), bullous (raised, >1 cm, with clear fluid), or pustular (raised with purulent fluid)?

      1. Are there petechiae (tiny pinpoint red dots from broken blood vessels), purpura (large flat area of blood under tissue), or ecchymosis (very large bruised area)? All can result from intradermal bleeding and need to be differentiated from erythema (redness of the skin). With erythema, the redness is cleared when pressed and returns when you release. With pressure, petechiae, purpura, and ecchymosis do not blanch. Petechiae on the lower body after a breech delivery or upper body with a vertex presentation can be normal. If widespread, petechiae are considered abnormal. Petechiae and purpura can signify thrombocytopenia and require a workup.

      1. Is there a history of a congenital infection? Obtain a thorough maternal history. TORCH infections are known to cause rashes. The "blueberry muffin baby" has widespread purpura and papules and can be seen in rubella (most known), CMV, and syphilis.

      1. Is the infant ill appearing? A well infant with a rash suggests a benign rash. A febrile or ill-appearing infant with a rash requires a thorough workup searching for an infectious cause.

      1. What medications did the mother receive during pregnancy and delivery? Is the mother breastfeeding and taking any medications? A rare cause of rash in the infant.

      1. Does the skin lesion make you think of a genetic disorder? Skin lesions can be associated with genetic syndromes.

          1. Blisters: Epidermolysis bullosa.

          1. Brown flat patches: Neurofibromatosis.

          1. Cutis marmorata: Cornelia de Lange syndrome and in trisomies 18 (Edward syndrome) and 21 (Down syndrome).

          1. Deficient hair and nails: Ectodermal dysplasias.

          1. Scaly, thick skin: Ichthyoses.

          1. Thin, fragile skin: Collagen disorders and hypoplasia of the dermis.

          1. Unformed skin: Aplasia cutis.

          1. White skin and hair: Piebaldism, tuberous sclerosis.

  3. Differential diagnosis

      1. Benign skin disorders/rashes that usually require no workup or intervention. These rashes are common.

          1. Erythema toxicum, the most common newborn rash, consists of erythematous macules with a central papule or pustule. Can be present at birth, typically appear within the first 48 h, and may appear up to 2 weeks of age. More common in full-term infants and more common on the trunk, extremities, and perineum. New lesions can appear after the initial onset and usually disappear after a week.

          1. Transient neonatal pustular melanosis. These 2- to 5-mm pustules are usually present at birth on various sites, typically the face and sacrum. Pustules evolve and disappear within 48 h but can leave hyperpigmented scarring that eventually resolves but may persist for months.

          1. Sebaceous ...

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