Multiple brown bumps in 9-month-old infant

The Case

A healthy 9-month-old boy is brought to the clinic by his mother, who is concerned about multiple golden-brown “bumps” on his trunk, head, arms, and legs that developed soon after birth. She noticed that every time one of these lesions gets irritated, it swells and forms a red pruritic plaque. The blistering had improved since the newborn period, and his growth and development have been normal. There is no family history of any skin disorders.

DIANOSIS: Urticaria pigmentosa

Darier sign (urtication or blistering of a lesion after scratching or stroking) is pathognomonic for UP. It is caused by release of histamine from mast cells secondary to mechanical trauma.^3,5 With increasing age it becomes more difficult to demonstrate the Darier sign. Although most infants and young children are not symptomatic, itching or signs of systemic histamine release (diarrhea, headache, gastrointestinal bleeding) may occur, necessitating further evaluation and treatment.

Systemic mastocytosis with bony and bone marrow involvement occurs in up to 2% of pediatric patients with UP and should be suspected in children with hepatosplenomegaly, flushing episodes, or peptic ulcer symptoms.² However, even children with severe symptoms usually improve spontaneously by 5 to 10 years of age and most lesions regress. Progressive improvement can occur well into adolescence.

DIFFERENTIAL DIAGNOSIS

Urticaria pigmentosa lesions can be mistaken for urticaria, which are transient and not usually associated with hyperpigmentation.⁴ Pigmented nevi are mostly brown and black rather than golden brown and do not urticate. Café-au-lait macules present as uniform brown macules or patches and never have the leathery texture so characteristic of UP.

DIAGNOSIS

The diagnosis of pediatric UP usually is a clinical one, and the Darier sign is diagnostic. Biopsies are reserved only for lesions that are clinically inconsistent with UP.⁵ Systemic studies rarely are needed, but when systemic symptoms are present, the initial workup consisting of complete blood count with differential, chemistry panel, and liver enzymes is recommended.⁵ Skeletal surveys and bone marrow biopsies are warranted only in patients with UP with severe systemic symptoms.²