These are clinical presentation, histopathology, direct immunofluorescence (DIF) microscopy and indirect immunofluorescence (IIF).13 PV is characterised histologically by intraepithelial blister formation and immunofluorescence studies showing immunoglobulin G (IgG), immunoglobulin A (IgA) and/or complement component 3 (C3) binding on the cell surfaces of keratinocytes. Here, C3 is linked to acquired polycythemia vera.