Differentiating Infection from Inflammation in Systemic Vasculitis

Clinical Assessment

A structured clinical assessment at each visit is essential to detect new organ involvement and differentiate between active vasculitis, infection, and other complications, as recommended by the European League Against Rheumatism 1, 2
Patients with systemic vasculitis should be managed in collaboration with, or at centers of expertise, as accurate assessment requires expert guidance to differentiate activity from damage and consider differential diagnoses, according to the American College of Rheumatology 1
Multiorgan involvement is common in primary systemic vasculitis, necessitating a systematic approach to evaluation, as stated by the European League Against Rheumatism 1

ANCA testing (including indirect immunofluorescence and ELISA) should be performed in the appropriate clinical context to help establish diagnosis and monitor disease activity, as recommended by the American College of Rheumatology 1, 2
Serial determination of inflammatory markers such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) is recommended, but results must be interpreted in the context of clinical findings, according to the European League Against Rheumatism 3
Urinalysis and other basic laboratory tests should be conducted at each clinical visit to monitor disease activity, particularly in patients with renal involvement, as stated by the American College of Rheumatology 1, 2
Complete blood count may show leukocytosis in both infection and active vasculitis, but marked neutrophilia with left shift more strongly suggests infection, as reported in the Kidney International journal 4

Appropriate imaging studies should be performed based on clinical presentation and suspected organ involvement, as recommended by the American College of Radiology 5
In cases where infection is suspected, targeted imaging of the potentially affected area should be performed, according to the American College of Radiology 2, 5

A positive biopsy is strongly supportive of vasculitis and is recommended to assist diagnosis and further evaluation for patients suspected of having vasculitis, as stated by the American College of Rheumatology 1, 2
Biopsy can be particularly helpful for distinguishing active disease from damage as the cause of clinical decline, according to the European League Against Rheumatism 2
Histopathological evidence of vasculitis, such as fibrinoid necrosis or pauci-immune glomerulonephritis, remains the gold standard for the diagnosis of vasculitis, as reported by the American College of Rheumatology 1
Repeat kidney biopsy may differentiate recurrent or refractory disease activity from infection or alternative diagnoses, as stated by the European League Against Rheumatism 2

Conduct thorough clinical assessment for signs of infection or vasculitis activity, and obtain appropriate laboratory tests (complete blood count, inflammatory markers, cultures if indicated, ANCA), as recommended by the American College of Rheumatology 1, 2
If infection is suspected, obtain appropriate cultures before starting antibiotics, and consider empiric antibiotic therapy based on likely pathogens, as reported in the Kidney International journal 4
Temporarily reduce immunosuppression if infection is confirmed, as stated by the European League Against Rheumatism 2

Patients on immunosuppressive therapy are at increased risk for opportunistic infections, which may present atypically, as reported by the American College of Rheumatology 2
Pneumocystis jirovecii pneumonia prophylaxis should be considered in patients on significant immunosuppression, as recommended by the Kidney International journal 4
Certain infections (e.g., bacterial endocarditis) can mimic ANCA-associated vasculitis and should be excluded before intensifying immunosuppression, as stated by the European League Against Rheumatism 2