Toxic Megacolon

Generality

Toxic megacolon is an "abnormal gaseous distension of the colon, with acute onset, independent of obstructive processes. The major total or segmental dilation of the colic walls causes symptoms such as abdominal swelling and pain, fever and shock.

Toxic megacolon is a very serious condition and can be lethal when not treated with the utmost urgency and in an appropriate manner. The "toxic" attribute distinguishes it from other non-toxic forms of colic distension, such as congenital ones (Hirschsprung ), idiopathic or pseudo-obstructive (Ogilvie's syndrome). In particular, we speak of toxic megacolon to underline the presence of symptoms of systemic toxicity (such as mental confusion) attributable to alterations in electrolyte homeostasis and acid-base balance.

Causes

Disorders associated with Toxic Megacolon

• Chronic inflammatory bowel disease
  • Ulcerative colitis
  • Crohn's disease
• Infectious colitis
  • Salmonella, Shighella, amoebic colitis
  • Clostridium difficile (pseudomembranous colitis)
  • Cytomegalovirus colitis
• HIV / AIDS
• Chemotherapy for cancer
• Ischemic colitis, especially in the elderly
• Complications of diverticular diseases, especially in the elderly
• Stenosing colon cancers, especially in the elderly
• Sepsis, states of shock, MOF, etc.

Toxic megacolon is a complication of inflammatory bowel disease. Ulcerative colitis and Crohn's disease represent the most common causes of toxic megacolon in Italy and in other industrialized countries, while in developing regions and among debilitated patients, toxic megacolons due to infectious processes of the colon leading to colitis prevail. pseudomembranous.

Unlike what happens in common colitis, in the presence of toxic megacolon the inflammatory process is not limited to the superficial layers of the intestinal walls (mucosa), but also goes deep into the submucosal, muscular and serous tunics. By affecting the nerve endings of the plexuses, the inflammatory process can cause muscular paralysis of the colon, with the arrest of the progression of the enteric content and consequent distension. Due to the increased pressure, the local venous and arterial vessels are progressively occluded, facilitating necrotic and perforative processes. Furthermore, the absorption of water and electrolytes through the intestinal mucosa is compromised.

By way of example, toxic megacolon complicates 5 to 10% of cases of ulcerative colitis, while it is rarer among people with Crohn's disease. Today, thanks to the advent of new biological drugs that allow better control of inflammation, the onset of toxic megacolon as a complication of ulcerative colitis is becoming increasingly rare. Often, it occurs as an acute initial episode, less frequently during a phase and rarely in chronic and continuous forms of ulcerative colitis. More generally, therapeutic and pharmacological advances (eg antibiotic therapies and anti-retroviral drugs) have reduced the incidence of toxic megacolon as a complication of the aforementioned diseases. However, even drugs can be risk factors for the onset of toxic megacolon; this is the case, for example, of prolonged antibiotic therapies not compensated by the intake of probiotics: such treatment can cause intestinal dysbiosis with selection of resistant strains (Clostridium difficile pseudomembranous colitis, common in a hospital setting and difficult to treat). Even antidiarrheals, narcotics or anticholinergics - administered for the treatment of ulcerative colitis, of the m. Crohn's disease or a banal gastroenteritis, possibly viral - they can favor the onset of toxic megacolon slowing down, up to stopping, intestinal peristalsis

Symptoms and complications

For further information: Toxic Megacolon Symptoms

Clinically, toxic megacolon manifests itself with the typical picture of severe acute colitis, which can sometimes evolve dramatically, characterized by symptoms and signs of peritoneal involvement (peritonitis) and systemic toxicity:

• Worsening abdominal pain, localized or diffuse
• Abdominal swelling with considerable gaseous distension of the intestinal loops
• Abdominal pain exacerbated by pressure
• Absence or scarcity of intestinal peristalsis that typically occurs after a conspicuous diarrhea with numerous discharges (even 10-15 / day)
• Fever
• Tachycardia
• Dehydration
• Pallor
• Mental confusion or psychic agitation

The most fearful complication of toxic megacolon is intestinal perforation linked to the abnormal distension of the colic walls. The extension of the infectious-inflammatory process to the blood can be responsible for sepsis and shock (tachycardia, hypotension, nausea, profuse sweating, confusion) .

Diagnosis

In the absence of an improvement in general conditions, the paradoxical and sudden arrest of fecal emission in a patient suffering from profuse diarrhea until recently must always lead to suspect the onset of a toxic megacolon. Another important clinical sign is the critical reduction of abdominal listener noises (

Diagnostic confirmation is obtained from the blank radiograph of the abdomen, which in the presence of toxic megacolon shows an abnormal increase in the diameter of the colon (at least 6 cm at the level of the transverse colon), with possible signs of emphysema of the wall with detachment of the mucosa. A CT scan can then be performed. Biohumoral tests show leukocytosis, haemoconcentration, increased ESR and inflammation indices, anemia and electrolyte imbalances with a tendency to metabolic alkalosis (increase in blood pH).

The execution of a barium enema during a period of severe and acute diarrhea could represent a possible precipitating factor and is also contraindicated due to the high risk of perforation, especially if practiced with barium, a very sticky substance that if the colon were to break it would cause very severe peritonitis to be treated. The same goes for colonoscopy.

Treatment

In the presence of toxic megacolon, the goal of treatment is bowel decompression associated with the prevention of additional factors that can distend the colon. With reference to this last point, feeding by mouth is suspended to avoid the introduction of air and food; it is then replaced by enteral nutrition, with particular attention to restoring the electrolyte balance to prevent shock and dehydration. Corticosteroids may be indicated to suppress the inflammatory reaction when toxic megacolon is caused by "acute inflammatory bowel disease. Broad-spectrum antibiotics, administered intravenously, can instead be used to prevent sepsis or to treat a toxic megacolon. from Clostridium difficile, a bacterium complicated to eradicate and sensitive to vancomycin and fidaxomicin. At the same time it is important to discontinue all drugs that can reduce colon motility; these include narcotics, antidiarrheal and anticholinergic agents. Decompression occurs by aspiration through a nasogas tube trico, which absorbs and drains what is secreted in the stomach and duodenum, and a soft rectal probe, positioned with extreme caution to avoid perforation of the intestine. Contraindicated both the administration of purgative laxatives, especially the irritating ones, and the practice of evacuative enemas.

If decompression is not practicable, if the patient does not improve within 24-48 hours, or if the diameter of the bowel reaches or exceeds 12-13 cm, surgical removal of a more or less extended part of the body is required. colon (colectomy).