This 16-month-old boy had a brown papule on his left thigh at birth. In the early months of his life, the patient developed new brown and tan papules on his chest, back, and occipital scalp. Although his growth and development were normal, some of the papules occasionally blistered after rubbing or irritation and he had a few brief episodes of flushing. Urticaria pigmentosa is one manifestation of cutaneous mastocytosis. This condition is characterized by persistent pruritic pigmented skin lesions that uriticate with mechanical or chemical irritation. This finding is known as Darier’s sign. The condition is associated with mutations in the c-KIT protooncogene, which codes for the stem cell growth factor receptor (also known as the mast cell growth factor receptor). Urticaria pigmentosa can occur from birth to middle age with most cases occurring within the first 6 months of life. Cutaneous lesions consist of macules, papules, nodules, plaques, vesicle or bullae. Pruritus may be severe, and occurs as a result of the massive release of histamine from mast cell degranulation. Triggers for degranulation include alcohol, opiates, aspirin, quinine, scopolamine, gallamine, reserpine, amphotericin B, polymyxin, and tubocarine.
On histology, a dense dermal collection of mast cells is diagnostic of mastocytosis. Severe systemic disease may involve the lymph nodes, GI tract, bones, heart, blood, liver and spleen. The prognosis for isolated cutaneous involvement, such as in urticaria pigmentosa, is generally good. Most cases clear spontaenously or improve significantly over time. Symptomatic relief can be obtained with systemic anti-histamines. PUVA is frequently efficacious. Diarrhea as a result of urticaria pigmentosa can be controlled with oral cromolyn sodium. Avoidance of physical and chemical percipitants is of paramount importance for control of this condition.
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bronze 1-2 cm round to oval leathery plaques with fuzzy borders and one plaque with surrounding wheal