[Cryoglobulinemic vasculitis]

[Laboratory diagnostics for vasculitis beyond antineutrophil cytoplasmatic autoantibodies]

The diagnosis of systemic vasculitis (SV) is a major clinical challenge due to the very different forms of presentation and requires an interdisciplinary approach. Targeted laboratory diagnostics support making the diagnosis, differential diagnosis and classification and are also a key component in the detection of active organ manifestations and treatment complications. The basic laboratory tests include the erythrocyte sedimentation rate (ESR), C‑reactive protein (CRP), blood count, serum creatinine, urinalysis, specific autoantibodies, complement, immunoglobulins, cryoglobulins and hepatitis B and C serology. Antineutrophil cytoplasmic autoantibodies (ANCA), antiglomerular basement membrane antibodies (anti-GBM antibodies) and anti-C1q antibodies are valuable laboratory markers for the diagnosis of the various forms of small vessel vasculitis. There are no specific laboratory tests for the diagnosis of medium and large vessel vasculitis. Despite advances in our understanding of the pathogenesis of vasculitis, no biomarkers have yet been identified that can be reliably used to guide treatment or that are useful in distinguishing vasculitis from other inflammatory diseases such as infections or treatment complications.

[Renal manifestations in vasculitides of small and medium-sized vessels]

Small-vessel vasculitides, in particular, are frequently manifested in the kidneys. A distinction is made between antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAV) and immune complex vasculitides. Even within the AAVs there are differences with respect to renal involvement, which manifest as necrotizing glomerulonephritis (GN) but renal involvement is much rarer in eosinophilic granulomatosis with polyangiitis than in microscopic polyangiitis and granulomatosis with polyangiitis. Disease progression, organ manifestation and prognosis vary according to the ANCA status. In immune complex vasculitides (cryoglobulinemic vasculitis, IgA vasculitis, hypocomplementemic urticarial vasculitis and antiglomerular basement membrane, GBM, disease), endothelial-adjacent activation of neutrophilic granulocytes leads to local vessel wall damage with subsequent ischemic tissue damage, similar to AAV. The sparse evidence of immune complexes is different in pauci-immune AAV. Polyarteritis nodosa is a disease with variable clinical presentations with necrotizing vasculitis of small and medium-sized arteries. Intrarenal aneurysms and hemorrhages but not GN lead to renal damage. Diagnostically, the detection of specific autoantibodies (e.g. anti-GBM), cryoglobulins or increased complement turnover can be decisive. Renal biopsy with qualified immunohistopathology is particularly important in cases of initial manifestation and unclear constellation of findings. The treatment of renal vasculitis is adapted to the severity, stage of disease, extrarenal organ manifestation and pathogenesis. It ranges from glucocorticoid monotherapy to moderate immunosuppression, up to targeted biologic therapy, chemotherapy and plasmapheresis.