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Cutaneous mastocytosis: Telangiectasia macularis eruptiva perstans (TMEP)

Diagnosis: Telangiectasia macularis eruptiva perstans (TMEP)

Cutaneous mastocytosis include solitary mastocytoma, diffuse erythrodermic mastocytosis, paucicellular mastocytosis (telangiectasia macularis eruptiva perstans [TMEP]), and urticaria pigmentosa (UP).
Urticaria pigmentosa is the most common form and is characterized by multiple oval or round red-brown macules, papules, or plaques.
On stroking, a urticaria pigmentosa or mastocytoma lesion becomes pruritic, edematous, and erythematous (the Darier sign), caused by mast cell degranulation. The Darier sign is not positive in patients with TMEP because the lesions are paucicellular.
In TMEP, epidermis is normal. Dermis shows spindled mast cells best identified by Giemsa or Toluidine  blue stain showing cytoplasmic granules. Mast cells are positive with CD 117 immunostain.