Patients with a clinical picture suggestive of GPA are three times more likely to have a C-ANCA, rather than a P-ANCA. Stone et al. determined that the sensitivity of ANCA is only 60%; however, the specificity can be quoted up to 99% (if both ELISA and immunofluorescence testing are done). Further, in GPA, 80–90% of patients are PR3 positive, compared with only 10–20% MPO positive. The presence of positive-PR3 antibodies was later determined to have prognostic value in treating patients with GPA.8 In disease limited mostly to upper respiratory airways, ANCA may be negative in up to 40% of cases. That will make diagnosis even more challenging.
GPA can also affect the kidneys in up to 80% of cases, especially during the first two years of the disease.3 Detecting renal involvement early is difficult, but essential. New avenues were opened by a study of Ohlsson et al. that assessed the use of urinary biomarkers, such as cytokines (IL-6, IL-8) and monocyte chemoattractant protein-1 (MCP-1). This study demonstrated that MCP-1 levels in urine were significantly higher in ANCA-vasculitis patients (in the stable phase of the disease) compared with healthy controls. Further, patients with higher urinary levels of MCP-1 and IL-6 tend to relapse more within three months and have poor prognoses.9 In 2012, a study by Lieberthal et al. determined that increased urinary MCP-1 concentrations were able to discriminate between active renal disease and remission. It was noted that a 1.3-fold increase in MCP-1 had 94% sensitivity and 89% specificity for active renal disease.10 Thus, in addition to conventional markers of disease activity, such as CRP, ANCA and vasculitis activity scores, urinary MCP-1 can be a promising prognostic marker.
We would also like to emphasize the role of biopsy to establish a clear diagnosis. Most often, skin and renal biopsies are obtained in patients to diagnose ANCA vasculitis. Nasal biopsy is rarely performed due to fear of nonspecific results, but these may be valuable to rule out other non-inflammatory causes, infections and malignancy. Typical findings are chronic inflammation and capillaritis, but granulomatous features are diagnostic for GPA, especially in patients with limited disease and negative ANCA. Borner et al. showed that the sensitivity of sinonasal mucosal biopsy in localized disease was about 53% compared with C-ANCA antibodies of 47%.11
As previously mentioned, our patient had nasal biopsy-proven disease that showed both granulomatous changes and neutrophilic infiltration of the intima of the small blood vessels.
