Urticaria Pigmentosa

Photoclinic

The mother of an 18-month-old boy was concerned that for the past year, the child had nonbloody, watery stools at least twice a day and a worsening rash. The child had a history of failure to thrive; his weight had decreased from the 56th percentile at 7 months to the 4th percentile at 12 months. The rash initially looked like pink “bug bites” but darkened over time to look more like moles. The lesions did not seem to bother the child, but the mother noticed that they became red with warm baths.

The patient’s weight was at the 2nd percentile, height at the 23rd percentile, and head circumference at the 26th percentile. Multiple brown-tan, maculopapular lesions of 3 to 5 mm were scattered over the trunk, neck, and arms. They developed a surrounding area of redness when stroked with a tongue blade. The remaining physical findings were normal.

A complete blood cell (CBC) count, chemistry panel, liver enzyme levels, erythrocyte sedimentation rate, and tryptase level were all normal. Results of stool culture and testing for ova and parasites, reducing substances, fecal leukocytes, and occult blood were negative.

Urticaria pigmentosa was diagnosed on the basis of the clinical findings. It is 1 of 4 cutaneous mastocytosis disorders that result from an abnormal amount of mast cells proliferating in the skin: urticaria pigmentosa (the most common form), solitary mastocytoma, diffuse cutaneous mastocytosis, and telangiectasia macularis eruptiva perstans.¹ These disorders do not directly involve other organs but may present with systemic symptoms, such as flushing, blistering, itching, shortness of breath, hypotension, and GI upset (eg, reflux, diarrhea).^1,2 Symptoms may be present at birth but most commonly appear before age 2 years; a male predominance has been reported.^2,3 Most symptoms resolve over time, and about 50% resolve by adolescence.¹

Diagnosis is clinical. The cardinal feature is urtication and erythema of lesions after gentle rubbing (Darier sign).^1,2 The lesions can be mistaken for moles or café au lait macules. A biopsy showing mast cell infiltration of the dermis confirms the diagnosis.⁴

Laboratory studies are generally unnecessary; however, if lesions do not improve, screening tests to rule out mastocytosis are frequently ordered. These include a CBC count, chemistry panel, and levels of liver enzymes and tryptase.¹ Results of these studies in this patient were normal. We believe that his GI symptoms were caused by an endocrine effect from cutaneous histamine release.

Treatment is aimed at minimizing mast cell mediator–induced symptoms. Avoidance of triggers, both physiologic (pressure, heat, and cold) and chemical (polymyxin B sulfate, thiamine, NSAIDs, iodine contrast, and systemic anesthetics), is important.¹ H1 blockers can help with flushing and pruritus, whereas H2 blockers can help with diarrhea or peptic ulcers.¹ Topical cortico-steroids can be used as adjunct therapy for cutaneous symptoms. Other treatments include cromolyn sodium and oral ketotifen, although the latter is only available outside the United States.¹

Prognosis is good when urticaria pigmentosa is diagnosed early. This patient was treated with a combination of cetirizine and ranitidine for his cutaneous and GI symptoms. At follow-up one month later, his stools were more formed and his weight increased to the 14th percentile.