Gastrointestinal disease

Chapter 6 Gastrointestinal disease






Gastrointestinal symptoms and signs







Vomiting


Many gastrointestinal (and non-gastrointestinal) conditions are associated with vomiting (Table 6.1). This is controlled by a complex reflex involving central neural control centres located in the lateral reticular formation of the medulla which are stimulated by the chemoreceptor trigger zones (CTZs) in the floor of the fourth ventricle, and also by vagal afferents from the gut. The central zones are directly stimulated by toxins, drugs, motion sickness and metabolic disturbances. Raised intracranial pressure has a direct effect on the vomiting centre leading to vomiting. Luminal toxins, inflammation and mechanical obstruction are local GI causes of vomiting.


Table 6.1 Causes of vomiting: some examples










Nausea is a feeling of wanting to vomit, often associated with autonomic effects including salivation, pallor and sweating. It often precedes actual vomiting. Retching is a strong involuntary unproductive effort to vomit associated with abdominal muscle contraction but without expulsion of gastric contents through the mouth.


Faeculent vomit suggests low intestinal obstruction or the presence of a gastrocolic fistula.


Haematemesis is vomiting fresh or altered blood (‘coffee-grounds’) (see p. 254).


Early-morning nausea and vomiting is seen in pregnancy, alcohol dependence and some metabolic disorders (e.g. uraemia).


Persistent nausea alone is often stress-related and is not due to gastrointestinal disease.



Flatulence


This term describes excessive wind. It is used to indicate belching, abdominal distension, gurgling and the passage of flatus per rectum. Swallowing air (aerophagia) is described on page 296. Some of the swallowed air passes into the intestine where most of it is absorbed, but some remains to be passed rectally. Colonic bacterial breakdown of non-absorbed carbohydrate also produces gas. Rectal flatus thus consists of nitrogen, carbon dioxide, hydrogen and methane. It is normal to pass rectal flatus up to 20 times/day. Causes of increased gas production and intake include high-fibre diet and carbonated drinks.




Abdominal pain


Pain is stimulated mainly by the stretching of smooth muscle or organ capsules. Severe acute abdominal pain can be due to a large number of gastrointestinal conditions, and normally presents as an emergency (see p. 298). An apparent ‘acute abdomen’ can occasionally be due to referred pain from the chest, as in pneumonia or to metabolic causes, such as diabetic ketoacidosis or porphyria.


Check:











Examination of the abdomen







Examination of the rectum and sigmoid colon


A digital examination of the rectum should be performed in all patients with a change in bowel habit, rectal bleeding and prior to proctoscopy or sigmoidoscopy.






Investigations


Routine haematology and biochemistry, followed by endoscopy and radiology, are the principal investigations. The investigation of small bowel disease is discussed in more detail on page 267. Manometry is mainly used in oesophageal disease (see p. 237) and anorectal disorders (see p. 286).




Endoscopy


Video endoscopes have replaced fibreoptic instruments and relay colour images to a high definition television monitor. The tip of the endoscope can be angulated in all directions. Channels in the instrument are used for air insufflation, water injection, suction, and for the passage of accessories such as biopsy forceps or brushes for obtaining tissue, snares for polypectomy and needles for injection therapies. Permanent photographic or video records of the procedure can be obtained.



image Oesophagogastroduodenoscopy (OGD, ‘gastroscopy’) is the investigation of choice for upper GI disorders with the possibility of therapy and mucosal biopsy. Findings include reflux oesophagitis, gastritis, ulcers and cancer. Therapeutic OGD is used to treat upper GI haemorrhage and both benign and malignant obstruction. Relative contraindications include severe chronic obstructive pulmonary disease, a recent myocardial infarction, or severe instability of the atlantoaxial joints. The mortality for diagnostic endoscopy is 0.001% with significant complications in 1 : 10 000, usually when performed as an emergency (e.g. GI haemorrhage).


image Colonoscopy allows good visualization of the whole colon and terminal ileum. Biopsies can be obtained and polyps removed. Benign strictures can be dilated and malignant strictures stented. The success rate for reaching the caecum should be at least 90% after training. Cancer, polyps and diverticular disease are the commonest significant findings. Perforation occurs in 1 : 1000 examinations but this is higher (up to 2%) after polypectomy (see Practical Box 6.2).


image Balloon enteroscopy, either double or single balloon, can examine the small bowel from the duodenum to the ileum using specialized enteroscopes in expert centres.


image Capsule endoscopy is used for the evaluation of obscure GI bleeding (after negative gastroscopy and colonoscopy) and for the detection of small bowel tumours and occult inflammatory bowel disease. It should be avoided if strictures are suspected.



image Practical Box 6.2


Gastroscopy and colonoscopy







Imaging


Full clinical information must be provided before the examination, and ideally, the images obtained should be reviewed with the radiologist to aid interpretation. The optimal technique to be used will depend on local expertise.


Plain X-rays of the chest and abdomen are chiefly used in the investigation of an acute abdomen. Interpretation depends on analysis of gas shadows inside and outside the bowel. Plain films are particularly useful where obstruction or perforation is suspected, to exclude toxic megacolon in colitis and to assess faecal loading in constipation. Calcification may be seen with gall bladder stones and in chronic pancreatitis, though CT is more sensitive for both.


Ultrasound involves no radiation and is the first-line investigation for abdominal distension, e.g. ascites, mass or suspected inflammatory conditions. It can show dilated fluid-filled loops of bowel in obstruction, and thickening of the bowel wall. It can be used to guide biopsies or percutaneous drainage. In an acute abdomen, ultrasound can diagnose cholecystitis, appendicitis, enlarged mesenteric glands and other inflammatory conditions.



Computed tomography involves a significant dose of radiation (approximately 10 millisieverts). Modern multislice fast scanners and techniques involving intraluminal and intravenous contrast enhance diagnostic capability. Intraluminal contrast may be positive (Gastrografin or Omnipaque) or negative (usually water). The bowel wall and mesentery are well seen after intravenous contrast especially with negative intraluminal contrast. Clinically unsuspected diseases of other abdominal organs are quite often also revealed (Fig. 6.5a).




Magnetic resonance imaging. MRI uses no radiation and is particularly useful in the evaluation of rectal cancers and abscesses and fistulae in the perianal region. It is also useful in small bowel disease and in hepatobiliary and pancreatic disease.


Positron emission tomography (PET) relies on detection of the metabolism of fluorodeoxyglucose. It is used for staging oesophageal, gastric and colorectal cancer and in the detection of metastatic and recurrent disease. PET/CT adds additional anatomical information.





Contrast studies



image Barium swallow examines the oesophagus and proximal stomach. Its main use is for investigating dysphagia.


image Double-contrast barium meal examines the oesophagus, stomach and duodenum. Barium is given to produce mucosal coating and effervescent granules producing carbon dioxide in the stomach create a double contrast between gas and barium. This test has a high accuracy for the detection of significant pathology – ulcers and cancer – but requires good technique. Gastroscopy is a more sensitive test and enables biopsy of suspicious areas.


image Small bowel meal or follow-through specifically examines the small bowel. Ingested barium passes through the small bowel into the right colon. The fold pattern and calibre of the small bowel are assessed. Specific views of the terminal ileum can be obtained and are used to identify early changes in patients with suspected Crohn’s disease.


image Small bowel enema (enteroclysis) is an alternative specific technique for small bowel examination. A tube is passed into the duodenum and a large volume of dilute barium is introduced. It is particularly used to demonstrate strictures or adhesions when there is suspicion of intermittent obstruction. Generally, this has been replaced by MR enteroclysis.


image Barium enema examines the colon and is used for altered bowel habit. Colonoscopy and CT colonography have largely replaced this examination for rectal bleeding, polyps and inflammatory bowel disease.


image Absorbable water-soluble (Gastrografin or Omnipaque) contrast agents should be used in preference to barium when perforation is suspected anywhere in the gut.



Radioisotopes


Radionuclides are used to a varying degree depending on availability and expertise. Some more common indications and techniques:



image Detect urease activity of Helicobacter pylori13C urea breath test (see p. 249)


image Assess oesophageal reflux – gamma camera scan after oral [99mTc]technetium-sulphur colloid


image Measure rate of gastric emptying – sequential gamma camera scans after oral [99mTc]technetium-sulphur colloid or 111In-DTPA (indium-labelled diethylene triamine penta-acetic acid)


image Demonstrate a Meckel’s diverticulum – gamma camera scan after i.v. [99mTc]pertechnetate, which has affinity for gastric mucosa


image Assess extent of inflammation and presence of inflammatory collections in inflammatory bowel disease – gamma camera scan after i.v. 99mTc-HMPAO (hexamethylpropylene amine oxime) labelled white cells


image Evaluate neuroendocrine tumours and their metastases – gamma camera scan after i.v. radiolabelled octreotide or MIBG (meta-iodobenzylguanidine)


image Assess obscure gastrointestinal bleeding – gamma camera abdominal scan after i.v. injection of red cells labelled with 99mTc (only useful if the bleeding is >2 mL/min)


image Measure albumin loss in the stools (in protein-losing enteropathy) – following albumin labelled in vivo with i.v. 51CrCl3. This test has been replaced by the measurement of the intestinal clearance of α1 antitrypsin


image Assess bile salt malabsorption (in patients with unexplained diarrhoea) – gamma camera scan to measure both isotope retention and faecal loss of orally administered 75selenium-homocholic acid taurine (SeHCAT) (see p. 293)


image Detect bacterial overgrowth in the small bowel – measure 14CO2 in breath following oral 14C glycocholic acid.



The mouth


The oral cavity extends from the lips to the pharynx and contains the tongue, teeth and gums. Its primary functions are mastication, swallowing and speech. Problems in the mouth are extremely common and, although they may be trivial, they can produce severe symptoms. Poor dental hygiene is often a factor.














The salivary glands


Excessive salivation (ptyalism) may occur prior to vomiting or be secondary to other intraoral pathology. It can be psychogenic.


Dry mouth (xerostomia) can result from a variety of causes:



The principles of management are to preserve what flow remains, stimulate flow and replace saliva (glycerine and lemon mouthwash and artificial saliva).




The pharynx and oesophagus






Structure and physiology

The oesophagus is a muscular tube approximately 20 cm long that connects the pharynx to the stomach just below the diaphragm. Its only function is to transport food from the mouth to the stomach. In the upper portion of the oesophagus, both the outer longitudinal layer and inner circular muscle layers are striated. In the lower two-thirds of the oesophagus, including the thoracic and abdominal parts containing the lower oesophageal sphincter, both layers are composed of smooth muscle.


The oesophagus is lined by stratified squamous epithelium, which extends distally to the squamocolumnar junction where the oesophagus joins the stomach, recognized endoscopically by a zig-zag (‘Z’) line, just above the most proximal gastric folds.


The oesophagus is separated from the pharynx by the upper oesophageal sphincter (UOS), which is normally closed due to tonic activity of the nerves supplying the cricopharyngeus. The lower oesophageal sphincter (LOS) consists of a 2–4 cm zone in the distal end of the oesophagus that has a high resting tone and, assisted by the diaphragmatic sphincter, is largely responsible for the prevention of gastric reflux.



Swallowing

During swallowing, the bolus of food is voluntarily moved from the mouth to the pharynx. This process is mediated by a complex reflex involving a swallowing centre in the dorsal motor nucleus of the vagus in the brainstem. Once activated, the swallowing centre neurones send pre-programmed discharges of inhibition followed by excitation to the motor nuclei of the cranial nerves. This results in initial relaxation, followed by distally progressive activation of neurones to the oesophageal smooth muscle and LOS. Pharyngeal and oesophageal peristalsis mediated by this swallowing reflex causes primary peristalsis. Secondary peristalsis arises as a result of stimulation by a food bolus in the lumen, mediated by a local intra-oesophageal reflex. Tertiary contractions indicate pathological non-propulsive contractions resulting from aberrant activation of local reflexes within the myenteric plexus.


The smooth muscle of the thoracic oesophagus and lower oesophageal sphincter is supplied by vagal autonomic motor nerves consisting of extrinsic preganglionic fibres and intramural postganglionic neurones in the myenteric plexus (Fig. 6.6). There are parallel excitatory and inhibitory pathways.




Symptoms of oesophageal disorders

Major oesophageal symptoms are:



Table 6.3 Causes of dysphagia












Investigations available for oesophageal disorders



image Barium swallow and meal.


image Oesophagoscopy.


image Manometry (Fig. 6.7) is performed by passing a catheter through the nose into the oesophagus and measuring the pressures generated within the oesophagus. It is used to assess oesophageal motor activity. It is not a primary investigation and should be performed only when the diagnosis has not been achieved by history, barium radiology or endoscopy. Recordings are usually made over a short time period, or much more rarely for up to 24 h. High resolution manometry has superseded conventional manometry and the greater concentration of pressure sensors enables the identification of a wider range of abnormalities of oesophageal function with a greater diagnostic accuracy.


image pH monitoring – 24-hour ambulatory monitoring uses a pH-sensitive probe positioned in the lower oesophagus and is used to identify acid reflux episodes (pH <4). Catheter and implantable sensors are available; both are insensitive to alkali. Although only 5–10% of recorded acid reflux episodes are perceived by the patient, pH is a valuable means of correlating episodes of acid reflux with patient’s symptoms.


image Impedance uses a catheter to measure the resistance to flow of ‘alternating current’ in the contents of the oesophagus. Combined with pH it allows assessment of acid, weakly acid, alkaline and gaseous reflux, which is helpful in understanding the symptoms that are produced by a non-acid reflux. Treatment is, however, still difficult in these conditions.



Mar 31, 2017 | Posted by in GENERAL & FAMILY MEDICINE | Comments Off on Gastrointestinal disease
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