Generalized reddish-brown macules on a 51-year-old man.

Urticaria pigmentosa (UP) is characterised by brownish to reddish macules and papules with central body distribution. The histopathologic hallmark of UP lesions is the neoplastic infiltrates of mast cells in dermis. The prognosis factors associated with coexisting systemic involvement might include monomorphic lesions, adult-onset, tryptase levels, bone symptoms or osteoporosis, and constitutional or cardiovascular symptoms.