P-anca positive, negative mpo??? wegener's vasculitis suspected due to clinical symptoms. 6 yr old with juvenile arthritis.

Difficult case: Untreated Wegener's is almost uniformly fatal. It's unusual but not unheard-of in kids. And there are lab errors. The decision about whether to use cyclophosphamide should be made by an interdisciplinary team at a major center.

See below: Wegener's Granulomatosis can exist with negative MPO. If in doubt, the diagnosis can be confirmed (or changed) by renal biopsy. If these problems are in your 6 year old, rather than you, then she needs an evaluation for aggressive treatment. I would suggest an assessment in a major center by a rheumatologist familiar with the use of newer immunological treatments.

Autoimmune: The positive ANCA test supports the diagnosis of an autoimmune disorder but with a negative MPO test (of one the proteins in the neurophils targeted by the disease) the possible diagnoses are many including Wegener's, RA, and others. Further testing including a biopsy may be required.