Invasive intestinal amoebiasis

If amoebae are invading the wall of a patient's gut, the danger is that it may perforate. If you can make the diagnosis before it has done so, metronidazole will probably cure him. When his gut has perforated, treatment is much more difficult. There are three forms of perforation: (1) An extraperitoneal (''sealed') perforation. (2) The perforation of an amoeboma, or an amoebic ulcer, into the peritoneal cavity, in the absence of acute dysentery. (3) A similar perforation in the presence of acute dysentery (this is rare in patients on metronidazole).

He usually presents as an ''acute abdomen', but diagnosing that invasive amoebiasis is causing it is difficult, before laparotomy. Typically, he has abdominal pain, fever, diarrhoea, and pain in the right iliac fossa. Often, there is a history of diabetes, alcoholism, pregnancy, or trauma. When you examine him, you find a mass in his right iliac fossa, or rigidity masking its presence, and often a distended abdomen.

If amoebiasis is common in your area, maintain a high level of suspicion. It is better to start treatment on suspicion, than to miss a treatable disease. If possible, treat him non- operatively. Avoid surgery if you can, because his colon will be friable and difficult to suture. Fortunately, surgery is usually unnecessary, because the perforation will probably have been localized by his diseased colon sticking to his surrounding small gut and omentum.

If however his perforation is not sealing off, you may have to operate, even if he is a bad risk. If you leave him, he is sure to die, whereas an operation may save him.

At laparotomy you may find: (1) A large inflammatory mass in the region of his caecum. This is more likely to be a paracolic abscess than an amoeboma. (2) Greyish patches in his caecum. (4) Multiple and often adjacent perforations, most commonly in his caecum and sigmoid colon. (5) Inflammatory lesions elsewhere in his large gut.

If he is very ill, the less surgery you do, the better. Repairing a perforation is difficult, because his whole colon is usually affected, very friable and adherent to other organs. But, if his gut has perforated, you must divert his faecal stream somehow. Resection and exteriorization are bloody and shock- producing, but they do relieve obstruction, and they remove the focus of infection. A bypass is better tolerated. Exteriorization is probably the easiest operation. Whatever you do, the danger is that his caecum will burst and flood his peritoneum with faeces.

Avoid these mistakes: (1) Don't attempt a right hemicolectomy, which is more difficult, and is said to be more dangerous. (2) Don't try to oversew a perforation[md]a necrotic colon will not hold sutures.

SAROJ (45 years) was admitted with a history of fever, bloody diarrhoea, abdominal pain, and a tender right suprapubic mass. Scrapings from typical amoebic ulcers in her rectum showed trophozoites. After only two days treatment with metronidazole, she felt better, her diarrhoea improved, and her abdominal mass staarted to resolve.]][+3] MIRANDA (46) had fever, diarrhoea, and vague abdominal pain for several weeks, worse during the last few days. She had a tender indurated mass in her right lower quadrant. At laparotomy, she had acute necrotizing colitis of her caecum, with multiple perforations, and much sloughing tissue. After a right hemicolectomy, she recovered slowly. LESSONS (1) Patients often respond to metronidazole rapidly. (2) When surgery is indicated, it is difficult. Eggleston FC, Vergese M, Handa AK, ''Amoebic perforation of the bowel: diagnosis and management'. Tropical Doctor 1980;4:160[nd]167.

INVASIVE INTESTINAL AMOEBIASIS For chemotherapy and a summary of treatment methods, see Section 31.10.

SPECIAL TESTS. Examine the patient's warm stools for trophozoites, and look for amoebic ulcers with a sigmoidoscope. Take a scraping and examine it for amoebae. Take a biopsy of the adjacent mucosa and send it for histology. Look for the cysts of E. histolytica in his stools. Only some strains are invasive, but unfortunately it takes a sophisticated laboratory to tell which ones.

CAUTION ! You will not always find amoebae, so don't be misled by a negative finding.

THE DIFFERENTIAL DIAGNOSIS includes:

Suggesting a typhoid perforation[md]a 2-week history of fever and vague abdominal pain, which becomes acute when his gut perforates; intestinal bleeding is uncommon.

Suggesting ileocaecal tuberculosis[md]he is usually (but not always) less sick than with amoebiasis (unless tuberculosis is obstructing his gut). The mass in his right lower quadrant is not so large, or tender (unless it has perforated). The course of the disease is usually more chronic.

Suggesting an appendix abscess (uncommon in in the developing world)[md]pain which starts centrally and then moves to his right lower quadrant; no history of diarrhoea, especially no bloody diarrhoea; he is less toxic, and not so sick as with amoebiasis. The distinction is not important, because both need a laparotomy.

Suggesting carcinoma of the caecum (rare in the developing world)[md]he is not so ill, or so toxic, and he may have rectal bleeding. The mass is firm to hard, but not particularly tender. Subacute obstruction is more common.

NON-OPERATIVE TREATMENT [s7]FOR INVASIVE AMOEBIASIS INDICATIONS. Manage him non-operatively if you can. (1) An amoebic perforation of his large gut, producing localized peritonitis, as indicated by a mass. (2) A critically ill patient with prolonged fever, diarhoea, toxaemia, and peritonitis, who may need surgery later, if he is fit enough. (3) Acute toxic dilatation of the colon (see below).

METHOD. Correct his dehydration, hypovolaemia, and oliguria, and especially his hypokalaemia (A 15.3). Chronic diarrhoea can cause severe potassium deficiency (resulting in confusion, weakness, hypotension, and ileus) which you can correct simply, and dramatically improve his ''toxic' state. If he has lost much blood, replace it. Give him intravenous metronidazole 800 mg 8-hourly, and chloramphenicol (2.9). If you don't have intravenous metronidazole, give him 1 g rectally 8- hourly (2.9). For more details on chemotherapy, see Section 31.10.

Apply nasogastric suction to minimize distension from obstruction, or ileus. Monitor his blood pressure, his pulse, and his hourly urine output.

Mark the outline of the mass on his skin, before you start treatment. Note how tender and indurated it is. Thereafter, examine it 8-hourly. If it increases in size, or becomes more tender, or there is more guarding, prepare to operate[md]peritonitis is spreading. Fortunately, this is uncommon once therapy has started.

LAPAROTOMY [s7]FOR INVASIVE AMOEBIASIS INDICATIONS. (1)Frank peritonitis. (2) The failure of non-operative treatment (see above).

PREPARATION. Resuscitate him thoroughly, and follow all the steps described above for non-operative treatment[md]this is critical.

ANAESTHESIA. (1) General anaesthesia with relaxants (A 10.1). (2) Ketamine, intubation, and relaxants (A 8.1). When he is anaesthetized, and his muscles are relaxed, examine his abdomen again, and sigmoidoscope him. This may confirm the diagnosis, and determine if his sigmoid colon is disease free. If it is, you may be able to divert his faecal stream into it (see below).

EXPLORATION. Make a median or right paramedian incision. Open his peritoneal cavity, and examine it as for peritonitis (6.2). Gently feel for a mass.

If there are greenish-grey, gangrenous patches on his soggy, soft caecum, your diagnosis of invasive amoebiasis was correct. It may fall apart and leak as you touch it. If his whole colon looks oedematous and inflamed, this may also be invasive amoebiasis, but in an earlier stage.

If he has extensive caecal amoebiasis, management depends on the condition of the rest of his colon. The first three procedures are comparatively safe, because you don't have to manipulate his precarious caecum. The fourth is less so.

(1) If the rest of his large gut looks normal (unusual), you can divide his terminal ileum about 25 cm from his ileocaecal valve, and anastomose its proximal end to the side of his transverse colon (9-11). Close the distal cut end of his ileum in two layers, and push it back into his abdomen. If he survives, the continuity of his gut can be re-established later.

(2) If his transverse colon is diseased but his sigmoid is spared (unusual), do an ileosigmoid anastomosis.

(3) If his sigmoid is also diseased, do an ileostomy.

(4) If the necrotic patches are confined to his caecum, and the ascending and proximal parts of his transverse colon, but do not go beyond it, exteriorize them as described below.

If his large gut has ruptured extraperitoneally (unusual), drain it through stab wound incisions in his flanks, and introduce large catheters into it.

If you find generalized peritonitis, with no obvious local lesion, lavage his peritoneum thoroughly and instil tetracycline 1 g in 1000 ml (6.2). Close his wound, and rely on metronidazole and antibiotics to cure him. Some surgeons say they can always find a lesion.

If his whole colon shows necrotic patches, which look as if they are about to perforate, do an ileostomy. Or, drain his colon widely, close the wound, and rely on metronidazole and antibiotics.

If distension is excessive, decompress his small gut at the time of the anastomosis.

You will not have removed his infected caecum (except in (4) above), so insert drains through stab wounds on the right side of his abdominal wall down to and, if necessary, even into his caecum itself.

EXTERIORIZATION is easier than some of the above procedures. Do it as in Section 66.11 on large gut injury. Free his diseased proximal large gut, and lift it out of the wound with his terminal ileum. ''Double-barrel' his healthy ileum and the left half of his transverse colon with about 10 interrupted sutures (D, 9-19). Irrigate his peritoneal cavity, and close his wound, with the two sutured loops of gut coming out of its upper end. Cut off the diseased gut about 3 cm above the surface of his skin.

CAUTION ! Try to minimize the contamination of his peritoneal cavity as you do this, pack it off where you can. (2) Irrigate it before you close it. (3) Insert drains in his right subhepatic space and his right iliac fossa.

He will need to wear an ileostomy bag (9.5). If he recovers from his acute disease, the continuity of his gut can be restored in 5 to 7 weeks.

DIFFICULTIES [s7]WITH INTESTINAL AMOEBIASIS If he has a MASS in his large gut, don't forget the possibility of an AMOEBOMA. This usually responds rapidly to metronidazole and antibiotics, sometimes in only a few days.

If he has a STRICTURE, remember the possibility of post-amoebic fibrosis. You may need to dilate it with your finger, or through a sigmoidoscope.

Because amoebomas and postamoebic strictures are so rare in some areas, the danger is that you may think that he has a carcinoma. If you are in any doubt, try metronidazole, and, if possible, take a biopsy.

If you find a regular, firm, SAUSAGE-SHAPED MASS in his large gut, remember the possibility of intussusception (10.8). You may find that it has ulcerated, but the ulcers are unlikely to be amoebic.

If his AMOEBIASIS IS PARTICULARLY SEVERE, he may have ACUTE TOXIC DILATATION OF THE COLON (a similar condition is seen in ulcerative colitis). This is diagnosable radiologically, and may simulate a perforation. Treat him non-operatively.

If he BLEEDS SEVERELY FROM HIS COLON, this may be fatal, because it may look normal externally, so that you will not know where the blood is coming from. See Section 22.3.