Differential Diagnosis for Vascular Condition with Positive c-ANCA and PR-3

Single Most Likely Diagnosis

• Granulomatosis with Polyangiitis (GPA): This condition, formerly known as Wegener's granulomatosis, is a form of vasculitis that affects small- and medium-sized vessels. It is strongly associated with the presence of c-ANCA (cytoplasmic antineutrophil cytoplasmic antibodies) and PR-3 (proteinase 3) antibodies, which are key diagnostic markers.

Other Likely Diagnoses

• Microscopic Polyangiitis (MPA): Although more commonly associated with p-ANCA and MPO (myeloperoxidase) antibodies, some cases of MPA can be positive for PR-3, making it a consideration in the differential diagnosis.
• Eosinophilic Granulomatosis with Polyangiitis (EGPA): Formerly known as Churg-Strauss syndrome, this condition is another form of vasculitis that can occasionally present with positive c-ANCA and PR-3, though it is more typically associated with asthma and eosinophilia.

Do Not Miss Diagnoses

• Drug-Induced Vasculitis: Certain medications can induce vasculitis with ANCA positivity, including PR-3. Recognizing this condition is crucial as it may require immediate withdrawal of the offending drug.
• Infectious Diseases: Some infections can trigger the production of ANCA, including PR-3. Identifying an underlying infection is vital for appropriate treatment.

Rare Diagnoses

• Idiopathic Necrotizing Crescentic Glomerulonephritis: A rare renal condition that can present with ANCA positivity, including PR-3. It is characterized by severe glomerular injury and rapid progression to renal failure if not treated promptly.
• ANCA-Associated Vasculitis Limited to the Skin: A rare condition where vasculitis is confined to the skin and can be associated with c-ANCA and PR-3 positivity, without the systemic involvement seen in GPA or MPA.