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IgA Deposition DIF — SCE Rheumatology MCQ

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ModerateVasculitisIgA Deposition DIFSCE Rheumatology

A 50-year-old woman presents with palpable purpura. Histology of a skin biopsy shows leucocytoclastic small-vessel vasculitis, and direct immunofluorescence demonstrates predominant granular IgA deposition in dermal vessel walls. What is the most accurate interpretation of the immunofluorescence finding?

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Correct answer: A — It supports IgA vasculitis in an appropriate clinical context but is not independently diagnostic

Predominant granular IgA deposition in dermal small-vessel walls supports classification as IgA vasculitis when the clinical phenotype is compatible. It is not independently diagnostic: vascular IgA may occur in patients with leucocytoclastic vasculitis who do not otherwise meet clinical criteria for IgA vasculitis. ANCA-associated vasculitis is usually pauci-immune, so prominent IgA deposition does not establish that diagnosis. A drug can trigger cutaneous small-vessel vasculitis, but the immunofluorescence pattern does not identify the trigger. The finding is therefore clinically useful rather than wholly non-specific. It also does not establish SLE, which requires compatible clinical and serological evidence and may show deposition of multiple immunoreactants rather than isolated predominant vascular IgA.

Reference: Larson AR, Granter SR. Utility of immunofluorescence testing for vascular IgA in adult patients with leukocytoclastic vasculitis. American Journal of Clinical Pathology. 2014;142:370–374. https://pubmed.ncbi.nlm.nih.gov/25125628/