Classification Tree for the Diagnosis of Hypersensitivity Vasculitis

Hypersensitivity vasculitis may be diagnosed using a classification tree approach.

top level	second level	third level	diagnosis
palpable purpura present	medication at onset		HSV
	no medication at onset	age > 16	HSV
		age <= 16	non-HSV
palpable purpura absent	maculopapular rash present	eosinophils in biopsy	HSV
		no eosinophils in biopsy	non-HSV
	maculopapular rash absent	neutrophils in vessel walls	HSV
		no neutrophils in vessel walls	non-HSV

Surrogate marker:

• If the status of palpable purpura is not known, then neutrophils in vessel walls may be used.

Criteria	Comment
age at disease onset > 16 years
medication at disease onset	a medication was taken at the onset of symptoms that may have been a precipitating factor
palpable purpura	slightly elevated purpuric rash over one or more areas of the skin; the rash does not blanch with pressure and is not related to thrombocytopenia
maculopapular rash	flat and raised lesions of various sizes over one or more areas of the skin
biopsy involving arteriole and venule	granulocytes in a perivascular or extravascular location
eosinophils in biopsy	eosinophils in a venule or arteriole at any location

Patient Subsets	Findings
HSV patients	palpable purpura, medication at onset
	palpable purpura, no medication at onset, age > 16 years
	no palpable purpura, maculopapular rash, eosinophils in biopsy
	no palpable purpura, no maculopapular rash, neutrophils in vessel wall
non-HSV patients	palpable purpura, no medication at onset, age <= 16 years
	no palpable purpura, maculopapular rash, no eosinophils in biopsy
	no palpable purpura, no maculopapular rash, no neutrophils in vessel wall

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