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What is Hypersensitivity angiitis is seen in - and explain in detail?
HSP is not hypersensitivity angiitis. But the best answer amongst the given options is HSP because it is the most important differential of hypersensitivity angiitis.

Hypersensitivity angiitis 

Hypersensitivity vasculitis or hypersensitivity angiitis or leukocytoclastic angiitis is a small vessel vasculitis due to hypersensitivity reaction.
It is usually to a known drug, e.g. cefoperazone, autoantigens or infectious agents.
Immune complexes lodge in the vessel wall, attracting polymorphonuclear leukocytes who in turn release tissue-degrading substances leading to an inflammatory process.
Hypersensitivity angiitis usually presents with skin manifestation, e.g. palpable purpura, but sometimes nerves, kidneys, joints and heart may also be involved.

Diagnostic criteria

At least 3 out of the 5 criteria are required


Age > 16
Use of possible triggering drug in relation to symptoms.
Palpable purpura
Maculopapular rash
Skin biopsy showing neutrophil infiltrate around the vessel.

Henoch-schonlein purpura is the most important differential.