Clinical utility of ANCA tests for the dermatologist

In summary, cutaneous findings are not uncommon in WG or MPA. Unfortunately, cutaneous lesions may be nonspecific as these same patterns may also be seen in other systemic vasculitides or illnesses including classic polyarteritis nodosa or inflammatory bowel disease. Careful clinical examination and clinical pathologic correlation is required to confirm the diagnosis. Testing of antineutrophil cytoplasmic antibodies may play a significant role in the evaluation of patients suspected to have systemic vasculitis or another illness with presentations similar to WG. Only a positive c-ANCA IIF result together with a positive PR₃-ANCA result obtained by EIA, and a positive p-ANCA IIF result together with a positive MPO-ANCA EIA result are sensitive and specific for WG and MPA. Repeat ANCA testing is warranted to follow the course of the disease in patients who have proven WG or MPA, as levels correlate loosely with disease activity and relapses in the absence of ANCA are rare. A patient with LCV or other cutaneous findings suggestive of WG with a positive C-ANCA/PR₃-ANCA or p-ANCA/MPO-ANCA test result should be followed carefully for subsequent development of systemic disease manifestations even if there is no sign of internal organ involvement at the time of initial presentation.