. 2021 Oct 13;5(11):e646. doi: 10.1097/HS9.0000000000000646

Table 1.

Proposed Classification and Criteria of CM.

Variant and Subvariant(s)	Abbreviation	Features/Criteria
Maculopapular cutaneous mastocytosis	MPCM	Positive Darier’s sign^a
Maculopapular cutaneous mastocytosis	MPCM	Typical pigmented skin lesions
Urticaria pigmentosa	UP	Positive histology^b
		KIT mutation in lesional skin
Monomorphic variant	MPCM-m	Monomorphic skin lesions^c
Polymorphic variant	MPCM-p	Polymorphic skin lesions^c
Polymorphic variant		No signs/criteria of SM^d
Diffuse cutaneous mastocytosis	DCM	Positive Darier’s sign^a
		Diffuse involvement of the entire skin
		Positive histology^b
		Criteria for SM not fulfilled^d
Cutaneous mastocytoma		Positive Darier’s sign^a
Cutaneous mastocytoma		Positive histology^b
Isolated mastocytoma		One single lesion
Multilocalized mastocytomas		Two or 3 lesions
Multilocalized mastocytomas		No signs/criteria of SM^d

^aWhereas the Darier´s sign and typical skin lesions serve as major diagnostic criteria (in both the monomorphic and polymorphic variant), a positive histology and the presence of an activating KIT mutation serve as minor diagnostic criteria. In the case of atypical lesions or a negative Darier’s sign, the diagnosis of mastocytosis can still be established provided that minor criteria are fulfilled. In young children with typical mastocytoma, testing for the Darier’s sign is often avoided because of the risk to provoke systemic reactions. Testing for the Darier’s sign should always be done gently and only when needed for diagnosis.

^bHistologic examination includes standard stains and immunohistochemistry using antibodies against tryptase and KIT regardless of the variant (monomorphic or polymorphic). The numbers of KIT⁺/tryptase⁺ mast cells is usually elevated in lesional skin in patients with mastocytosis and skin involvement.

^cThe monomorphic variant is found in children and adults. When found in children, the likelihood that the lesions will persist into adulthood is high. Polymorphic skin lesions are detected in childhood MPCM but usually not in adults with CM or systemic mastocytosis. When detected in children, the likelihood that the polymorphic skin lesions will spontaneously disappear at or shortly after puberty (in adolescence) is high.

^dIn all adult patients, SM has to be excluded by staging investigations including bone marrow studies. In children, bone marrow studies are only performed when clinical signs and symptoms and/or laboratory findings are indicative of an advanced hematologic disease.

CM = cutaneous mastocytosis; SM = systemic mastocytosis.