Diagnosis

4 Diagnosis

The differential diagnosis of common presentations of IBD is shown in Tables 4.1, 4.2, 4.3 and 4.4. In younger patients (under 50 years) the main differential diagnoses, depending on presentation, include infection and irritable bowel syndrome. In older people (over 50 years), neoplasia, diverticular disease and ischemia require special consideration. The aims of investigation (Tables 4.5, 4.6) are to establish the diagnosis, its site, extent and activity, and to check for complications of the disease (Chapter 3) and its treatment (Chapters 5, 6 and 7).

Blood tests

Hematology. In patients presenting with abdominal pain and/or diarrhea, test results revealing anemia and raised platelet count may suggest active IBD but are not diagnostic. Those with extensive chronic terminal ileal Crohn’s disease may have low serum B₁₂, while a low red-cell folate may indicate active chronic inflammation, reduced intake or malabsorption. Iron deficiency is common, although not necessarily diagnostic of IBD.

TABLE 4.1 Causes of bloody diarrhea
Cause	Disease
Inflammatory	Ulcerative colitis	Crohn’s colitis	Behçet’s colitis
Infective colitis	Campylobacter Salmonella Shigella Clostridium difficile Yersinia Tuberculosis	Enterohemorrhagic Escherichia coli (VTEC/0157:H7) Amebiasis Schistosomiasis Cytomegalovirus* Herpes simplex*
Neoplastic	Colorectal cancer
Vascular	Ischemia
Iatrogenic	NSAIDs	Antibiotics	Irradiation
*Particularly in immunocompromised patients. NSAIDs, non-steroidal anti-inflammatory drugs.

TABLE 4.2 Causes of rectal bleeding
Cause	Disease
Inflammatory	Proctitis	Crohn’s disease
Sexually transmitted	Gonococcus Cytomegalovirus Herpes simplex	Atypical mycobacterium Chlamydia Kaposi’s sarcoma
Neoplasia	Colorectal polyps Colorectal cancer	Anal cancer
Vascular	Ischemia	Angiodysplasia
Iatrogenic	NSAIDs (oral or suppositories)	Irradiation
Other	Benign solitary rectal ulcer Diverticulosis (acute bleeds only)	Severe upper gastrointestinal bleeding
NSAIDs, non-steroidal anti-inflammatory drugs.

Biochemistry. Raised C-reactive protein (CRP) and low serum albumin levels suggest active disease in patients with established ulcerative colitis or Crohn’s disease; they are also suggestive, although not diagnostic, of IBD in those in whom the diagnosis has not yet been made. Low serum albumin, calcium, magnesium, vitamin D, zinc and essential fatty acid concentrations may be found in Crohn’s disease patients, while abnormal liver function tests may be found in those with hepatobiliary complications of IBD.

Serology. In patients presenting for the first time with diarrhea, a negative test for endomysial or transglutaminase antibodies usually excludes celiac disease. Most patients with ulcerative colitis and a minority with Crohn’s disease have circulating perinuclear antineutrophil cytoplasmic antibodies (pANCAs), but this test is not sufficiently sensitive or specific to be of diagnostic value. Antibodies to Saccharomyces cerevisiae (ASCA) are present in most patients with small-intestinal Crohn’s disease. Profiles of these and other antibodies, including those against bacterial antigens such as Escherichia coli outer membrane porin protein C (OmpC), Pseudomonas fluorescens (I2) and flagellin (CBir1), are being used in some countries (e.g. USA) as diagnostic aids in patients with IBD of uncertain type.

TABLE 4.3 Causes of abdominal pain, diarrhea and weight loss
Cause	Disease
Inflammatory	Crohn’s disease Ulcerative colitis Behçet’s colitis	Microscopic/lymphocytic/collagenous colitis*
Infections	See Table 4.1
Neoplasia	Colorectal cancer Pancreatic cancer Small-bowel lymphoma	Endocrine tumors (carcinoid, gastrinoma, VIPoma)
Endocrine	Thyrotoxicosis Diabetic autonomic neuropathy	Hypoadrenalism
Vascular	Ischemia
Iatrogenic	NSAIDs Antibiotics Laxative abuse	Irradiation Gut resections
Malabsorption	Celiac disease Bacterial overgrowth	Lactose intolerance^†
Other	Irritable bowel syndrome^†
*Pain and weight loss unusual. ^†Weight loss unusual. NSAIDs, non-steroidal anti-inflammatory drugs. VIPoma, vasoactive intestinal peptide-producing tumor.

For patients who have recently traveled to endemic areas, serology (as well as stool samples) should be checked for amebiasis, strongyloidiasis and schistosomiasis. The use of corticosteroids in such patients, in the mistaken belief that they have active IBD, can have fatal consequences. HIV testing should be done for those who have watery diarrhea.

Finally, in patients with newly diagnosed IBD, a panel of serological tests is requested to establish previous exposure to infections that could recrudesce during any future use of immunosuppressive medications (see Chapter 6).

TABLE 4.4 Causes of abdominal pain and mass in the right iliac fossa
Cause	Disease
Ileocecal
Inflammatory	Crohn’s disease	Appendiceal mass
Infective	Tuberculosis Ameboma	Actinomycosis
Neoplastic	Cecal carcinoma Lymphoma	Carcinoid tumor
Other	Fecal loading
Renal	Hydronephrosis Cysts	Neoplasia Transplant
Gynecologic	Ovarian cyst Neoplasia	Tubal mass, including ectopic pregnancy Endometriosis