Brownish macules or papules or nodules which urticate when stroked provide the symptomatology and the diagnosis of urticaria pigmentosa (mastocytosis). Urtication from mild injury (stroking) is the result of histamine release from dermal mast-cell nests. The brown color is due to hyperactive melanocytes in the overlying epidermis.
Young children with only one or a few lesions limited to the skin (Fig 1) account for about 80% of all cases. The lesions, which are usually nodular, fade gradually and by puberty are usually insignificant.
Onset during later childhood or adult life is a matter for concern. The lesions are usually more numerous and tend to be macular or papular (Fig 2). They may progress until the entire skin is diffusely infiltrated with mast cells (Fig 3) and until individual lesions can no longer be appreciated. Systemic symptoms due to histamine release occur frequently and include episodic flushing, pruritus, headache, nausea, diarrhea,
Halprin KM. The Pigmented Hive. JAMA. 1966;197(11):917. doi:10.1001/jama.1966.03110110141035