Cutaneous small-vessel leukocytoclastic vasculitis (LCV), in association with linear IgA disease (LAD)-type immunoreactant deposition along epidermal basement membrane zone

Summary: Leukocytoclastic vasculitis (LCV) is a cutaneous small-vessel vasculitis characterized by perivascular deposition of immune complexes. Linear IgA disease (LAD) is an autoimmune (subepidermal) vesiculobullous disorder demonstrating linear (non-granular) IgA deposition along the cutaneous basement membrane zone (BMZ). LCV and LAD are generally regarded as separate disease entities with different pathophysiology. A 69-year-old male presented with a red, non-blanching maculopapular rash on bilateral upper and lower extremities, concerning for LCV. The patient had a co-existent acute diarrheal illness, and no new medications. Skin biopsies demonstrated: (1) early small-vessel vasculitis, with subepidermal blistering, on H&E staining; and (2) superficial perivascular granular IgA, IgM and C3 deposition, combined with linear, homogenous BMZ IgA deposition, on direct immunofluorescence (DIF) studies. A diagnosis of LCV with features of LAD was made. Patients with overlapping clinical-histopathological-DIF features of LCV and LAD are rarely reported; and include drug-induced (vancomycin), paraneoplastic, and idiopathic causes. It is postulated that combined LCV-LAD findings may result from: (1) unique autoimmune response to an unidentified shared antigen, with novel IgA antibody binding to both epidermal and vascular BMZs; (2) circulating/in vivo IgA antibody in LAD that could activate the complement cascade, via non-classical pathways, leading to vasculitis; and/or (3) “epitope spreading” phenomenon.