Short bowel syndrome overview

# Overview
Short bowel syndrome is a malabsorption disorder caused by the surgical removal of the small intestine. Most cases are acquired, although some children are born with a congenital short bowel. It does usually not develop unless a person has lost more than two-thirds of their small intestine. Intestine has the ability to adapt following resection. Adaptation depends on multiple factors including individual, intestinal and therapeutic measurements. Successful adaptation depends on the length of remaining intestine, portion of the resected intestine, and early introduction of nutrition therapy. Total intestinal adaptation defines as when patient is weaned from parenteral nutrition. The hallmark of short bowel syndrome is diarrhea. Complications might happen due to malnutrition, surgery and parenteral nutrition. Management of short bowel syndrome consists of medical and surgical therapy. Medical therapy consists of nutritional therapy and pharmacotherapy. Patients who have severe or worsened malabsorption might require surgery including intestinal transplant. Effective measures must be adopted for secondary prevention of complications following total parenteral nutrition including liver disease, cholelithiasis, kidney stone, small bowel bacterial overgrowth, lactic acidosis, lactic acidosis.

# Historical Perspective
The first successful intestinal resection was performed in 1880. In 1935, Haymond following research on many patients with bowel resection, reported that 30 to 50% loss of bowel was well tolerated. Total parenteral nutrition (TPN) was introduced during 1960s which helped patients to survive following bowel resection.

# Classification
Based on the length of the remaining bowel, short bowel syndrome may be divided into end-jejunostomy, jejunocolonic anastomosis, ileocolonic anastomosis. Severity varies from mild to severe. All of them require home parenteral nutrition except ileocolonic anastomosis which has excellent prognosis and rarely needs parenteral nutrition. Based on the etiology, short bowel syndrome may be divided into three categories such as vascular abnormalities, mucosal disease of intestine and causes without preexisting intestinal disease.

# Pathophysiology
Short bowel syndrome occurrs as a result of bowel resection following various diseases of the gut such as Crohn's disease, malignancies, ischemia, and trauma. Short bowel syndrome occurs when the length of the small intestine is less than 2 meters and requires nutritional therapy to prevent malnutrition. Post bowel resection, adaptation might occur which includes structural, motility and functional changes in the remaining intestine. Changes usually start in the first 24 hours following bowel resection and last for about two years. Adaptation depends upon multiple factors including individual, intestinal and therapeutic measurements. Following bowel resection, adaptation occurs in three phases including acute, adaptive, and maintenance phases. Successful adaptation depends on the length of remaining intestine, portion of the resected intestine, and early introduction of nutrition therapy. The term total intestinal adaptation is used when the patient is weaned from parenteral nutrition. The main reason for malabsorption following bowel resection is reduced absorptive capacity of the small intestine due to loss of surface area. On gross and microscopic examination, the resected bowel segment may show the underlying causes including Crohn's disease, malignancies or ischemia.

# Causes
Short bowel syndrome in adults is usually caused by surgical removal of the intestine due to different diseases including Crohn's disease, mesenteric ischemia, malignancies or radiation enteritis. Less common causes include trauma, volvulus, adhesion and iatrogenic surgery on gastrointestinal system.

# Differentiating short bowel syndrome from Other Diseases

# Epidemiology and Demographics
The incidence and prevalence of short bowel syndrome is difficult to estimate. All the data is derived from patients receiving home parenteral nutrition. Therefore, there are different distributions around the world. The incidence of short bowel syndrome was estimated to be 1-2 cases per 100,000 individuals worldwide per year. The prevalence of short bowel syndrome is approximately 0.3-4 per 100,000 individuals in the USA to 0.1-4 per 100,000 individuals in Europe. It affects all age groups. There is no racial predilection to short bowel syndrome and is reported worldwide. Short bowel syndrome affects men and women equally.

# Risk Factors
Common risk factor for the development of short bowel syndrome may be iatrogenic including any operation on the gastrointestinal system.

# Screening
There is insufficient evidence to recommend routine screening for short bowel syndrome.

# Natural History, Complications, and Prognosis
The symptoms of short bowel syndrome usually develop immediately following bowel resection. Diarrhea may cause massive fluid and electrolyte loss. Immediately after surgery, intestinal adaptation develops in three phases, including acute, adaptive and maintenance phase. During the adaptation, structural, motility and functional changes occur. Patients need hydration and nutritional support via parenteral, enteral and oral routes. Length of remaining small bowel is the most important prognostic factor. Patients with more than 200 cm length of small bowel, usually do not need parenteral nutrition. Patients with shorter small bowel may not wean off from parenteral nutrition support. Complications might occur due to malnutrition, surgery and parenteral nutrition. Malnutrition presents with vitamin, mineral and essential fatty acids deficiencies. Complications related to surgery including thrombosis, infection, hemorrhage, atelectasis and anastomosis disruption might occur. Small intestinal bacterial overgrowth due to stasis and obstruction might also occur. Chronic liver disease following parenteral nutrition is a common complication in short bowel syndrome. There is no definite cure for short bowel syndrome. However, medications and nutritional therapy significantly improve the quality of life and survival of the patients. Prognosis of short bowel syndrome depends on the location and size of the bowel resection, underlying pathology, nutrition support, pharmacotherapy, and extent of intestinal adaptation. The 2 and 5-year survival rate of patients with short bowel syndrome are approximately 80% and 70%, respectively.

# Diagnosis

## Diagnostic Criteria
Short bowel syndrome is mainly diagnosed based on clinical presentation. There are no established criteria for the diagnosis of short bowel syndrome. History of bowel resection and clinical manifestation including diarrhea and malnutrition would confirm the diagnosis.

## History and Symptoms
The hallmark of short bowel syndrome is diarrhea. A positive history of operation on gastrointestinal system and symptoms of malabsorption is suggestive of short bowel syndrome. The most common symptoms of short bowel syndrome include dehydration, abdominal pain, and fatigue.

## Physical Examination
Patients with short bowel syndrome usually appear weak and tired. Physical examination of patients with short bowel syndrome is usually remarkable for signs of malabsorption, dehydration and abdominal tenderness.

## Laboratory Findings
Laboratory findings consistent with the diagnosis of short bowel syndrome include anemia, hypoalbuminemia, low level of vitamins, minerals, and micronutrients. Level of acute phase reactants is high. Abnormal liver function tests including elevated liver enzymes and bilirubin might be seen. Fluid and electrolyte imbalance might be present. Fecal fat test is usually positive.

## Electrocardiogram
There are no ECG findings associated with short bowel syndrome. In case of malnutrition and electrolyte imbalance, an ECG may be helpful. Hypokalemia might present with arrhythmia, ST segment depression, low T wave, prominent U waves and QRS prolongation. Hypocalcemia might present with QT interval prolongation. Hypomagnesemia might present with QT interval prolongation and ventricular and supraventricular arrhythmia.

## X-ray
An abdominal x-ray may be helpful in the diagnosis of short bowel syndrome. Abdominal x-ray helps to rule out ileus or intestinal obstruction. Upper gastrointestinal series might demonstrate strictures and dilation of the bowel.

## Ultrasound
There are no abnormal echocardiographic findings associated with short bowel syndrome. Ultrasound may be helpful in the diagnosis of complications of short bowel syndrome including gallstones and liver diseases. Doppler ultrasound might be used to diagnose venous thrombosis.

## CT scan
Abdominal CT scan with contrast may be helpful in the diagnosis of short bowel syndrome complications including dilation, obstruction of the bowel and signs of liver diseases.

## MRI
There are no MRI findings associated with short bowel syndrome.

## Other Imaging Findings
There are no other imaging findings associated with short bowel syndrome.

## Other Diagnostic Studies
There are no other diagnostic studies associated with short bowel syndrome.

# Treatment

## Medical Therapy
Management of short bowel syndrome is complicated and requires close collaboration of all medical team members including the physician, nutritionist, and nurse with the patient and their families. Medical therapy consists of nutritional therapy and pharmacotherapy. Nutritional therapy is essential for short bowel syndrome and to restore the intestinal adaptation. It could be provided through oral, enteral and parenteral routes. The ultimate goal is to provide necessary nutrients via oral route other than parenteral or enteral routes. All patients require enough fluid, electrolytes, supplements and calories. Medications are used to control symptoms of short bowel syndrome include antimotility agents, antisecretory agents, and trophic agents. Lifelong follow-up is usually needed.

## Surgery
Surgery is not the first-line treatment option for patients with short bowel syndrome. Surgery is usually reserved for patients with the goal to wean them off parenteral nutrition. Patients who have severe or worsened malabsorption might require surgery including intestinal transplant. Transplant is contraindicated in patients with active infection or malignancies. Approximately half of the patients with short bowel syndrome will require surgery. Bianchi procedure and serial transverse enteroplasty (STEP) are performed to lengthen dilated bowel. Stricturoplasty might be necessary. Intestinal transplant is reserved for patients who have life-threatening complications of intestinal failure, irreversible permanent total parenteral nutrition requirement and episodes of sepsis or loss of venous access.

## Primary Prevention
There are no established measures for the primary prevention of short bowel syndrome. However, treating underlying causes including Crohn's disease and malignancies might prevent short bowel syndrome.

## Secondary Prevention
There are several ways to prevent complications of short bowel syndrome. Management strategies and regular follow-up are needed to find and treat complications accordingly. Effective measures must be done for secondary prevention of complications following total parenteral nutrition including liver disease, cholelithiasis, kidney stone, small bowel bacterial overgrowth, lactic acidosis, lactic acidosis. Hydration, consuming supplements, antibiotic therapy, and regular monitoring with blood tests, ultrasound and scans are recommended.