Differentials
Coeliac disease
SIGNS / SYMPTOMS
May manifest later in adult life as well as in childhood.
Weight loss usually accompanies the diarrhoea.
Systemic symptoms include ataxia, convulsions, bone pain, short stature, infertility.
Increased risk of gastrointestinal malignancy.[39]
Papulovesicular rash over the extensor surfaces of legs and arms, trunk, buttocks, and neck if dermatitis herpetiformis present.[40]
INVESTIGATIONS
Routine laboratory biochemistry may reveal an iron and/or folic acid (rarely B12) deficiency anaemia, elevated parathyroid hormone, elevated alkaline phosphatase, and hypocalcaemia.
Tissue transglutaminase (TTG) antibodies are raised and endomysial antibodies (EMA) are positive. If coeliac serology is negative, IgA levels should be checked as 2% to 5% of patients with coeliac disease are IgA deficient.[39] TTG is more sensitive and EMA is more specific.
Small bowel biopsy will show abnormalities ranging from increase in intraepithelial lymphocytes and crypt hyperplasia to villous atrophy.[41]
Reduced bone mineral density is present in many patients.[42]
Sucrase-isomaltase deficiency
SIGNS / SYMPTOMS
Autosomal recessive inherited deficiency.
Symptoms are evoked by sugar, not milk.[43]
Homozygotes have lifelong symptoms, while heterozygotes may have mild symptoms as infants and no symptoms as adults.
Affects up to 10% of the Inuit population of Greenland, but only 0.2% of North Americans.[44][45]
INVESTIGATIONS
Stools contain non-hydrolysed sucrose; however, hydrolysation by a special technique is needed before testing for reducing substances.
Diagnosis usually achieved by sucrose hydrogen breath test.
As many studies report false positives, diagnosis may need to be confirmed by small-intestinal biopsy showing reduced sucrase-isomaltase.
Cow's milk protein intolerance
SIGNS / SYMPTOMS
Between 5% and 15% of infants present with symptoms suggesting adverse reactions to cow’s milk protein.[46]
Typically resolves by age 4-5 years.[47]
May be confused with extremely rare congenital form of lactase deficiency, but diarrhoea is less severe and does not always start on the first day of exposure to milk.
INVESTIGATIONS
Prick test with cow's milk and cow's milk proteins, specific IgE antibodies, and challenge test with cow's milk confirms diagnosis in most patients.
Tests for lactase deficiency are negative.
Giardiasis
SIGNS / SYMPTOMS
Diarrhoea caused by a waterborne parasite, Giardia lamblia (one of the two most common gastrointestinal parasites in the US). History of water contamination may suggest diagnosis.
Significant weight loss is common. Post-giardiasis lactose intolerance occurs in 20% to 40% of patients.[48]
INVESTIGATIONS
No peripheral leukocytosis or eosinophilia, and white cells are usually absent in stool samples. Multiple stool specimens are needed to reveal parasite.
Immunoassays for antigen detection and immunofluorescence for parasite are more accurate, and sensitivity and specificity are >90%.[49]
Irritable bowel syndrome
SIGNS / SYMPTOMS
Typically recurrent abdominal pain or discomfort associated with a change in stool frequency or form. Pain or discomfort may be relieved by defecation.
A large number of patients have coexistent (or underlying) lactose intolerance, and symptoms can worsen after ingestion of lactose.[1][50]
INVESTIGATIONS
There is no single diagnostic test to confirm diagnosis.
Coeliac serology, including tissue transglutaminase antibodies and endomysial antibodies, is negative.
Lactose hydrogen breath test is negative, except in patients where either underlying diagnosis is lactase deficiency or both conditions coexist.
Tropical sprue
SIGNS / SYMPTOMS
Chronic diarrhoeal illness initiated or sustained by a still undefined infection. Patients have usually lived for more than 1 month in countries where tropical sprue exists. Most patients have steatorrhoea and progressive weight loss.
Relapse rate is substantial in treated patients who remain in, or return to, areas where tropical sprue is endemic.[51]
INVESTIGATIONS
Low vitamin B12 and folate serum levels with megaloblastic anaemia, hypoalbuminaemia, hypocalcaemia, and hypomagnesaemia are present due to malabsorption. Other causes of malabsorption should be excluded.
Endoscopic and histological findings are similar to untreated coeliac disease, but negative tissue transglutaminase antibodies with normal serum IgA level will help with diagnosis.
Treatment with tetracycline for 6 months completely reverses intestinal and haematological abnormalities in most patients.[51]
Eosinophilic enteritis
SIGNS / SYMPTOMS
Can affect any part of the gastrointestinal tract and usually presents with anaemia and weight loss, as well as diarrhoea and abdominal pain.[52]
Up to 50% of patients may be atopic, or have a history of food intolerance or allergy.[53]
INVESTIGATIONS
Endoscopic or laparoscopic biopsy of affected bowel shows histology with significant eosinophilic infiltrates.[52]
Peripheral eosinophil count and serum IgE levels may be raised.
Autoimmune enteropathy
SIGNS / SYMPTOMS
Rare disorder that presents in infancy with severe intractable diarrhoea and faltering growth. It may be isolated or occur as part of IPEX (immunodysregulation polyendocrinopathy enteropathy X-linked) syndrome.[54]
INVESTIGATIONS
Small bowel biopsies show severe villous atrophy and extensive lymphocytic infiltration.
Anti-enterocyte antibodies, when present, confirm the diagnosis.[54]
Coeliac serology, including tissue transglutaminase antibodies and endomysial antibodies, is negative.
Small bowel bacterial overgrowth
SIGNS / SYMPTOMS
History may reveal conditions that alter motility, intestinal anatomy, and gastric acid secretion (e.g., use of proton pump inhibitors, and anatomical disturbances in the bowel such as diverticula, fistulae, and blind loops created after surgery).[55]
Improvement of diarrhoea after taking antibiotics for some other illness is suggestive of diagnosis.
INVESTIGATIONS
Culture of jejunal fluid grows in excess of 10⁵ bacteria/mL.
A peak of breath hydrogen excretion within 2 hours from the ingestion of 50 g of glucose or 10 g of lactulose is consistent.
A trial of treatment with antibiotics for 1 week may help in the diagnosis if symptoms show an improvement.
Microscopic colitis (lymphocytic or collagenous)
SIGNS / SYMPTOMS
Watery diarrhoea and weight loss, as well as abdominal pain.[56]
Usually affects middle-aged patients, but can affect children, particularly those with a history of other auto-immune illnesses.[56]
Normal physical examination.
INVESTIGATIONS
A small number of patients may have slight anaemia, hypokalaemia, and high erythrocyte sedimentation rate, but positive auto-antibodies is more common.
Colonoscopy usually shows macroscopically normal colonic mucosa, though mild mucosal oedema, erythema, and friability may be seen. Colonic biopsies reveal changes typical of microscopic colitis, including either increased intra-epithelial lymphocytes (lymphocytic colitis) or sub-epithelial collagen deposition (collagenous colitis).
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