Approach
The diagnosis is clinical, based on a history of bowel resection with or without signs of fluid, electrolyte, nutritional, or micronutrient deficiency despite adequate enteral intake. Not all patients with SBS have intestinal failure; patients with mild disease remain nutritionally autonomous and the malabsorption is overcome by increasing oral intake. It is important that the surgeon measures the amount of residual bowel, not the amount resected. However, a patient’s ability to develop and maintain nutritional autonomy is not dependent solely on the amount of residual bowel, but rather on the health and function of that bowel. It must be recognized that patients with Crohn disease, despite SBS, may develop disease recurrence.
The aim of assessment is to distinguish SBS from intestinal failure due to active Crohn disease, cancer, or celiac disease; identify and thoroughly assess fluid, electrolyte, nutritional, or micronutrient deficiencies; and define the anatomy and bowel length. It is particularly important to distinguish SBS from malabsorption secondary to active Crohn disease, as the management of these conditions is very different. It is also important to remain alert for complications of long-term parenteral nutrition (PN) use.
History
A detailed review of the surgical history of the patient is crucial to obtain information about the intestinal anatomy. Symptoms of possible complications of SBS should also be specifically sought in the history.
Surgical history: if the patient has Crohn disease, the extent of disease should be established. If there has been surgery, it is important to know the length of remaining bowel and which segments have been removed. The health of the residual bowel is important.
Diet and weight: detailed information about the diet and the time frame of weight loss should be sought. Patients often struggle to maintain weight despite intentional hyperphagia and nutritional supplementation. The degree of weight loss is directly proportional to the reduction in absorptive capability of the bowel.
Diarrhea: diarrhea results from increased osmolarity of the intestinal contents (mostly due to fat malabsorption), bile salt irritation of the colon, decreased intestinal transit time, increased gastric acid production, and a decrease in gut surface area for water reabsorption. In addition, patients with a proximal jejunostomy may have a secretory response to food ingestion.
Volume depletion: it is important to determine whether there have been previous admissions for intravenous hydration, home use of oral rehydration solution, or symptoms of diarrhea or decreased urine output.
Fatigue: a direct consequence of vitamin deficiency, weight loss, and volume depletion.
Symptoms of vitamin deficiency: night blindness (vitamin A); proximal muscle weakness or bone fractures (vitamin D); excessive bleeding (vitamin C or K); motor weakness/altered gait or new neurologic deficits (vitamins E and B12).
Symptoms of liver disease related to SBS/intestinal failure: key symptoms include pruritus and confusion, and a key sign is jaundice.
Pain suggestive of new gallstones (postprandial epigastric or right upper quadrant abdominal pain) or kidney stones (dysuria or renal colic).
Symptoms of D-lactic acidosis: balance or vision difficulties, confusion, inappropriate behavior. This occurs due to oral carbohydrate overload, resulting in excess fermentable carbohydrate within the colon which is metabolized by colonic flora into D-lactate. Therefore, this complication is unlikely to occur in a patient without colon in continuity with small intestine.
Physical exam
Physical signs are related to the malabsorption of fluid, electrolytes, and nutrients.
Weight loss: weight and height should be measured to assess SBS-associated weight loss.
Volume depletion: dry mucous membranes, low skin turgor, tachycardia, and hypotension.
Peripheral or presacral edema due to protein depletion: protein depletion is the result of protein malabsorption, or decreased albumin synthesis due to PN-related liver failure.
Signs of neurologic dysfunction related to vitamin E or B12 deficiency: these may include orthostatic hypotension, asterixis (wrist tremor during dorsiflexion), altered reflexes, sensory deficits, and less commonly motor weakness or altered gait.
Dermatologic signs suggestive of deficiency in vitamins, zinc, or essential fatty acid: these may include swelling and fissuring of the lips (vitamin B2 deficiency); bruising/ecchymoses at nontraumatic sites (vitamin C deficiency); spontaneous bleeding (vitamin C or K deficiency); skin rash (zinc deficiency); and "chicken skin" on the backs of the arms (essential fatty acid deficiency).
In addition, if the patient is receiving home PN, it is important to examine central lines for exit site and subcutaneous tunnel infection. Liver disease is a known complication of long-term PN and it is important to look for any evidence of jaundice, asterixis, ascites, edema, or gastrointestinal (GI) bleeding, which are signs of end-stage liver disease.
Initial investigations
Laboratory investigations
CBC: anemia can develop due to deficiency of iron, copper (microcytosis), folate, or vitamin B12 (macrocytosis). Thrombocytopenia may suggest hemolysis due to vitamin E deficiency or PN-associated liver disease. Increased hemoglobin values indicate hemoconcentration and volume depletion.
Serum electrolytes, BUN, creatinine, and albumin are indicated to assess for electrolyte abnormalities, volume depletion, and hemoconcentration (elevated albumin, BUN/creatinine ratios, and contraction alkalosis, concurrent with elevated hemoglobin values). Hypo- and hypernatremia reflect hydration status. Hypokalemia is very common in SBS and reflects nutritional deficiencies as well as possible magnesium deficiency. Magnesium deficiency may exist in spite of a normal serum magnesium concentration and, if clinically indicated, measurement of 24-hour urine magnesium may be required for diagnosis. Serum bicarbonate concentration may be elevated in a dehydrated patient, or may be low in a patient who has significant losses from a duodenal fistula or diarrhea, or who has developed D-lactic acidosis as a consequence of excessive oral carbohydrate intake.
Serum calcium, zinc, selenium, folate, and vitamins A, B1, B2, B6, B12, C, D, and E must also be tested. Methylmalonic acid (MMA) can be used to confirm vitamin B12 deficiency. An INR is used to detect vitamin K deficiency. Deficiencies in the fat-soluble vitamins A and D are commonly seen in SBS. Vitamin E concentration should be measured in relation to total serum lipid concentration. Vitamin K deficiency is rare in patients who have an intact colon (where vitamin K is synthesized by bacteria) and who have not received oral broad-spectrum antibiotics. Water-soluble vitamin deficiencies are very rare in SBS (except for B12) due to efficient proximal absorption.
Additional investigations
Laboratory investigations
Serum hepatic aminotransferases, alkaline phosphatase, and bilirubin to monitor for intestinal failure-associated liver disease. An increase in alkaline phosphatase in patients supported with PN nutrition can be an early marker of liver damage and cholestasis.
Urinalysis to distinguish protein malabsorption from excessive protein loss due to nephrotic syndrome. It is also indicated to test for hematuria in patients with suspected kidney stones.
Serum D-lactate to exclude D-lactate acidosis in the presence of neurologic signs such as confusion or altered gait. In patients with SBS, carbohydrates may be metabolized by colonic bacteria to D-lactate; excessive oral carbohydrate intake can therefore lead to D-lactate acidosis. This can be a particular problem, as patients are encouraged to increase their oral intake to overcome malabsorption. Note that, because lactic acid measurement provided by most laboratories only measures L-lactate, testing for D-lactate has to be specifically requested.
Fecal fat quantification can be helpful in confirming/estimating fat malabsorption.
Radiology
Radiologic investigations are not required for diagnosis, but can be used as an additional test to define bowel length and anatomy. It is also useful to assess and monitor complications.
Upper GI contrast series may be used to estimate bowel length and anatomy if they remain unclear following patient history. Results should be carefully interpreted in the context of clinical findings, since radiologic length does not always correlate with function.
Dual-energy x-ray absorptiometry (DXA) scanning is used annually to monitor bone density, as patients are at high risk for osteopenia and osteoporosis due to vitamin D and calcium deficiencies. Z-scores for lumbar spine and femoral neck, in a study of patients requiring PN, were -3.35 ± 3.49 and -2.23 ± 2.11, respectively.[20] In some patients with SBS, corticosteroids to treat Crohn disease may further increase the risk of osteoporosis.
An abdominal ultrasound should be performed in all patients who present with postprandial epigastric or right upper quadrant abdominal pain to exclude cholecystitis.
A CT of the abdomen or renal ultrasound should be performed if patients present with dysuria, hematuria, or renal colic, as these patients are at high risk for calcium oxalate kidney stones.
Use of this content is subject to our disclaimer