Urticaria Pigmentosa (UP, or Maculopapular Cutaneous Mastocytosis (MPCM))

General: UP is the most frequent form of cutaneous mastocytosis (CM).

Clinical: In children, UP lesions tend to be papular. There is a subvariant which has non-pigmented plaques occurring primarily in infants. Adult lesions are usually macular, more darkly pigmented, and may be associated with telangiectasia. Some call these darkly pigmented lesions sometimes termed telangiectasia macularis eruptiva perstans subvariant (TMEP). Others reserve the term TMEP for an even more rare form with minimal or no increase in mast cells and relatively few but larger (>1cm) lightly pigmented lesions.

Microscopic: In children, UP lesions have aggregates of elongated or spindle-shaped mast cells which typically fill the papillary dermis and follow the vascular network into the reticular dermis. In adults, lesions may have fewer mast cells and it may require additional levels, sections, or biopsies to reveal aggregates or diagnostically high numbers of mast cells.

Stains:

• Positive:
• Negative:
• Suggested, focused panel:

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