This is an uncommon blistering subepidermal eruption of the skin associated with a gluten-sensitive enteropathy. Rarely there may be gross malabsorption, but usually the jejunal morphological abnormalities are not as severe as in coeliac disease. The inheritance and immunological abnormalities are the same as for coeliac disease. The skin condition responds to dapsone but both the gut and the skin will improve on a gluten-free diet.
This is a condition presenting with malabsorption that occurs in residents or visitors to a tropical area where the disease is endemic. Malabsorption of a mild degree, sometimes following an enteric infection, is quite common and is usually asymptomatic. The term tropical sprue is reserved for severe malabsorption (of two or more substances) that is usually accompanied by diarrhoea and malnutrition. Tropical sprue is endemic in most of Asia, some Caribbean islands, Puerto Rico and parts of South America. Epidemics occur, lasting up to 2 years, and in some areas repeated epidemics occur at varying intervals of up to 10 years.
The aetiology is unknown, but is likely to be infective because the disease occurs in epidemics and patients improve on antibiotics. A number of agents have been suggested but none has been shown to be unequivocally responsible. Different agents could be involved in different parts of the world. An overgrowth of coliforms that produce an enterotoxin has been reported.
These vary in intensity and consist of diarrhoea, anorexia, abdominal distension and weight loss. The onset is sometimes acute and occurs either a few days or many years after being in the tropics. Epidemics. can break out in villages, affecting thousands of people at the same time. The onset can also be insidious, with chronic diarrhoea and evidence of nutritional deficiency. The clinical features of tropical sprue vary in different parts of the world, particularly as different criteria are used for diagnosis.
ACUTE INFECTIVE causes of diarrhoea must be excluded (see p. 228), particularly Giardia, which can produce a syndrome very similar to tropical sprue.
MALABSORPTION should be demonstrated, particularly fat and vitamin BI2 malabsorption.
THE JEJUNAL MUCOSA is abnormal, showing some villous atrophy (partial villous atrophy). In most cases the lesion is less severe than that found in coeliac disease, although it affects the whole small bowel. Mild changes can be seen in asymptomatic individuals in the tropics, so jejunal mucosal changes must be interpreted carefully.
Many patients improve when they leave the sprue area and take folic acid (5 mg daily). Most patients also require an antibiotic (usually tetracycline 1 g daily) to ensure a complete recovery; it may be necessary to give this for up to 6 months. The severely ill patient requires resuscitation with fluids and electrolytes for dehydration; any nutritional deficiencies should be corrected. Vitamin Bl2 (1000 /-Lg) is also given to all acute cases.
The prognosis is excellent. Mortality is usually associated with water and electrolyte depletion, particularly in epidemics. Bacterial overgrowth The upper part of the small intestine is almost sterile, containing only a few organisms derived from the mouth. Gastric acid kills most organisms and intestinal motility keeps the jejunum empty. The normal terminal ileum contains faecal-type organisms, mainly Escherichia coli and anaerobes. Bacterial overgrowth is normally only found associated with a structural abnormality of the small intestine, although it can occur alone in the elderly. Aspiration of the upper jejunum will reveal the presence of E. coli and/or Bacteroides, both in concentrations greater than 106/rnl as part of a mixed flora. These bacteria are capable of deconjugating and dehydroxylating bile salts, so that uncnjugated and dehydroxylated bile salts can be detected in aspirates by chromatography. Steatorrhoea (see p. 202) occurs as a
result of conjugated bile salt deficiency.
The bacteria are able to metabolize vitamin BI2 and interfere with its binding to intrinsic factor, thereby leading to vitamin BI2 deficiency; this can be demonstrated using the Schilling test. Conversely some bacteria produce folic acid.
Bacterial overgrowth has only minimal effects on other substances absorbed from the small intestine. The clinical features are chiefly diarrhoea, steatorrhoea and vitamin BI2 deficiency, although this is not so severe as to produce a neurological deficit.
Although bacterial overgrowth may be responsible for the presenting symptoms, it must be remembered that many of the symptoms may be due to the underlying small bowel pathology.
If possible, the underlying lesion should be corrected, e.g. a stricture should be resected. With multiple diverticula, grossly dilated bowel, or in Crohn’s disease, this may not be possible and rotating courses of antibiotics are necessary, such as metronidazole and tetracycline, or ciprofloxacin.
Intestinal resection is usually well tolerated, but massive resection is followed by the short-gut syndrome. The effects of resection depend on the extent and the areas involved.
EXTENT. Because the gut is long, a 30-50% resection can usually be tolerated without undue problems. lleal resection The ileum has specific receptors for the absorption of bile salts and vitamin B12, so that relatively small resections will lead to malabsorption of these substances. Removal of the ileocaecal valve increases the incidence of diarrhoea. In ileal resection:
• Bile salts and fatty acids enter the colon and interfere with water and electrolyte absorption, causing diarrhoea.
• Increased bile salt synthesis can compensate for loss of approximately one-third of the bile salts in the faeces. Greater loss than this results in decreased micellar formation and steatorrhoea, and lithogenic bile and gallstone formation.
• Increased oxalate absorption is caused by the presence of bile salts in the colon. This gives rise to renal oxalate stones.
• There is a low serum vitamin B12 and macrocytosis.
INVESTIGA TION. This includes a small bowel followthrough, measurement of vitamin Bw bile salt and occasionally fat absorption.
MANAGEMENT. Many patients require vitamin B12 replacement and some need a low-fat diet if there is steatorrhoea. If diarrhoea is a problem, cholestyramine or aluminium hydroxide mixture to bind bile salts sometimes helps.
Here the ileum can take over jejunal absorptive function. Jejunal resection may lead to gastric hypersecretion with high gastrin levels; the exact mechanism of this is unclear. Intestinal adaptation takes place, with an increase in the absorption per unit length of bowel. Massive resection (short-gut syndrome) This can occur following resection in Crohn’s disease, mesenteric occlusion or trauma. Diarrhoea with severe loss of water and electrolytes occurs together with malnutrition. Parenteral nutrition (sometimes long term) is necessary. With intestinal adaptation most will eventually recover, although they continue to have diarrhoea and little functional reserve should another gastrointestinal problem occur.