ASCA : Role as diagnostic & prognostic marker in inflammatory bowel diseases
The inflammatory bowel diseases (IBD) are a heterogeneous group of disorders of unknown etiology. The group is primarily subdivided into ulcerative colitis (UC) and Crohn's disease (CD). Although CD & UC are generally considered distinctive forms of IBD, their clinical presentations may overlap. Despite several clinical, endoscopic, radiological and histopathological tools, in approximately 1% of cases no differentiation can be made. The disease in these patients is called indeterminate colitis (IC). Indeed the clinical overlaps and presence of IC support the concept that IBD represents a spectrum of diseases rather than two entities, CD and UC.
Accurate diagnosis of IBD is very important. Because the treatment strategies in CD and UC differ, especially when surgery is required, much effort has been expended over the years to distinguish the cases. Non-invasive tests are expected to display a crucial role in the differential diagnosis. In IBD, investigators have searched for several years for antibodies that correlate with various diseases. Two antibodies for use in the clinical diagnosis of IBD have been identified, i.e. Antisaccharomyces Cerevisiae Antibody (ASCA) and Perinuclear Antineutrophil Cytoplasmic Antibody (P-ANCA). Combined detection of ASCA and P-ANCA has been proposed as a valuable diagnostic approach in IBD.
ASCA have been found to be significantly more prevalent in patients with CD compared to patients with UC. These antibodies include antibodies of both IgG and IgA classes.
The presence of IgG or IgA ASCA has been shown to have a high specificity for CD. Furthermore, a recent report found the presence of both IgG and IgA ASCA was 100% specific for CD.
P-ANCA may have significant diagnostic value for UC (prevalence 65%). Positive P-ANCA in CD has been proposed as a predictor for UC - like phenotype.
Medical therapy for CD is not curative, and relies on a variety of approaches to suppress bowel inflammation. As reliable indicators of prognosis are lacking, medical therapy is usually guided by signs and symptoms. Published data indicate that 80% of CD patients require surgery by 20 years while 20-40% requires surgery within 3 years. As resection is not curative, surgery is usually reserved for medically refractory disease.
Patients with CD, who are positive for ASCA IgA, IgG, or both, may define a subset of patients with CD at increased risk for early surgery.
In conclusion, ASCA and P-ANCA have an important role in identifying disease subgroups and might enable clinicians to modify treatment strategies.