PRTN3 and Henoch-Schoenlein purpura: Serology will be positive for anti-proteinase 3(Antineutrophil cytoplasmic antibody) which is highly specific for W G. The differential diagnosis for WG includes polyarteritis nodosa, Churg-Strauss, Henoch-Schonlein purpura, temporal arteritis and Takayasu syndrome (Table 2).