Diagnosis of renal damage in Wegener's granulomatosis

Laboratory diagnostics of Wegener's granulomatosis

Patients with Wegener's granulomatosis have a number of non-specific laboratory changes: increased ESR, neutrophilic leukocytosis, thrombocytosis, normochromic anemia, and in a small percentage of cases, eosinophilia. Dysproteinemia with increased globulin levels is typical. Rheumatoid factor is detected in 50% of patients. The main diagnostic marker of Wegener's granulomatosis is ANCA, the titer of which correlates with the degree of vasculitis activity. Most patients have c-ANCA (to proteinase-3).

Differential diagnosis of Wegener's granulomatosis

Diagnosis of Wegener's granulomatosis is straightforward in the presence of the classic triad of signs: damage to the upper respiratory tract, lungs and kidneys, especially when ANCA is detected in the blood serum. However, on average, 15% of patients have a negative test for antibodies to neutrophil cytoplasm. For this reason, morphological examination of organs and tissues is of great importance for the diagnosis of Wegener's granulomatosis.

• In patients with respiratory tract lesions, biopsy of the nasal mucosa and paranasal sinuses is highly informative, revealing necrotizing granulomas, although in some cases only non-specific inflammation is detected. Biopsy of the skin, muscles, nerves, and, if necessary, lungs can also be of great help in diagnosing the disease.
• A renal biopsy is indicated for all patients with Wegener's granulomatosis with clinical signs of glomerulonephritis. In addition to establishing a histological diagnosis (pauci-immune necrotizing glomerulonephritis), this procedure allows determining the treatment strategy and prognosis, which is especially important for patients admitted to a nephrologist with a clinical picture of severe renal failure (blood creatinine over 440 μmol/l), which sometimes develops several months after the onset of the disease. In this case, only a renal biopsy can distinguish rapidly progressing glomerulonephritis with a high degree of activity (which requires aggressive immunosuppressive therapy, which should be carried out by starting treatment with hemodialysis) from terminal renal failure with diffuse glomerulosclerosis, in which treatment with immunosuppressants is already futile.

Differential diagnostics of Wegener's granulomatosis with kidney damage is carried out with other diseases that occur with the development of renal-pulmonary syndrome.

Causes of renal-pulmonary syndrome

• Goodpasture's syndrome
• Wegener's granulomatosis
• Polyarteritis nodosa
• Microscopic polyangiitis
• Churg-Strauss syndrome
• Henoch-Schönlein purpura
• Cryoglobulinemic vasculitis
• Systemic lupus erythematosus
• Antiphospholipid syndrome
• Pneumonia in:
  • acute poststreptococcal glomerulonephritis;
  • acute interstitial drug-induced nephritis;
  • glomerulonephritis in patients with subacute infective endocarditis;
  • acute tubular necrosis.
• Lymphomatoid granulomatosis
• Primary or metastatic tumors of the kidneys and lungs
• Pulmonary embolism due to renal vein thrombosis complicating nephrotic syndrome
• Sarcoidosis
• Uremic lung

One of the differential diagnostic tasks is to distinguish between Wegener's granulomatosis and other forms of systemic vasculitis that occur with similar clinical symptoms.

Rapidly progressive glomerulonephritis in Wegener's granulomatosis should be differentiated from rapidly progressive glomerulonephritis without extrarenal signs of vasculitis, which is also a pauci-immune ANCA-associated glomerulonephritis and is considered a local renal form of vasculitis. Due to the morphological identity and the same serological markers, differential diagnosis in these cases is difficult, which, however, is not always important, since the treatment tactics are the same (immediate, even before the results of histological and serological studies are obtained, administration of glucocorticoids and cytostatics).

Differential diagnosis of Wegener's granulomatosis also requires the need to distinguish lung lesions within the framework of this form of systemic vasculitis from opportunistic respiratory infections, mainly tuberculosis and aspergillosis, the development of which is often noted during treatment with immunosuppressants.

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