The surgery of intestinal amoebiasis

Amoebiasis is usually a ''medical' disease, but it does have some surgical complications, ranging from the very acute to the very chronic, which you should be able to treat. They usually involve a patient's gut, but they can involve his liver (31.12), or occasionally his lungs, or even his skin. Amoebiasis is more common in older patients, but no age is immune, and amoebae may invade the gut of babies. It is less often seen in women, but in pregnancy it can be fulminating.

Entamoeba histolytica normally lives harmlessly in the colon, but trophozoites occasionally invade its mucosa to cause shallow discrete circular or oval ulcers, with yellow sloughs in their bases, and sometimes red edges. These ulcers are most common in the caecum and ascending colon, the sigmoid colon, and the rectum. They cause diarrhoea, with or without blood, pus, and mucus.

The lesions in the gut are usually quite superficial, but, if a patient's resistance is low, amoebae may invade it more deeply, especially if he is diabetic, or alcoholic, or has recently been severely injured. Invasive intestinal amoebiasis takes several acute forms: (1) Amoebae can cause massive necrosis of the mucosa of his colon, so that large pieces of it separate as casts, and are passed rectally. (2) They can invade its muscular wall to cause gangrene, sloughing, and perforation[md]acute necrotizing amoebic colitis. Bacterial infection may then spread as generalized peritonitis, or it may remain localized as a pericolic abscess which you can feel as a tender mass. He can also develop peritonitis, without actual perforation, or his gut can perforate extraperitoneally. As the result of this suppuration, it may obstruct, or he may develop ileus. Occasionally, his colon bleeds severely.

If the pathological process is more chronic, he may have: (1) An amoeboma; this is a diffuse, oedematous, hyperplastic granulomatous swelling anywhere in his colon or rectum, which is often multiple, and may be palpable, and may obstruct his gut (usually temporarily). Although an amoeboma may form anywhere, a mass in the caecum is more easily palpable. If you do feel a mass in a patient with amoebiasis, it is more likely to be a paracolic abscess than an amoeboma. (2) A fibrous postamoebic stricture, which is one of the end results of an amoeboma. An amoeboma and a stricture are two stages in the same process, and he may have a lesion with some of the features of both. Both are common in some areas (Durban), and are the late, chronic complications of amoebic colitis; they occur years after the initial bloody diarrhoea, and are less serious than acute invasive amoebiasis. They usually involve the rectum (where you can feel them rectally), the sigmoid, and the descending colon, in that order. Both can: (1) cause diarrhoea and other abdominal symptoms, and (2) obstruct the large gut, usually incompletely.

AMOEBIASIS CHEMOTHERAPY. Some drugs act on amoebae in the gut, some on amoebae in the tissues, and some on both. The patient will need drugs to treat both. So, if necessary, give him him more than one drug.

If he is very ill, and amoebae have spread beyond his gut, give him metronidazole, and either dehydroemetine (or emetine), or chloroquine, or both. Emetine is the most potent tissue amoebicide.

(1) Metronidazole (a tissue and lumenal amoebicide) 400 to 800 mg by mouth 8-hourly for 7 to 10 days. Children 10 to 15 mg/kg 8-hourly. If possible, also give him an infusion of 500 mg as a 0.5% solution over 8 hours.

(2) Dehydroemetine (a tissue amoebicide) 1.25 mg/kg/day, maximum dose 90 mg, by intramuscular injection for a maximum of 10 days. Don't repeat the course before 28 days. Or, less satisfactorily, give him emetine in the same way, 1 mg/kg, maximum 60 mg.

(3) Chloroquine (a tissue amoebicide) 150 mg of chloroquine base 4 times daily for 2 days, followed by 150 mg twice daily for 19 days. Children 10/mg/kg/day.

(4) Tetracycline (active against associated bacteria) 500 mg 4 times daily for 5 days (only effective for intestinal amoebiasis).

(5) Diloxanide furoate (''Furamide', ''Entamide furoate', a lumenal amoebicide) 500 mg 8-hourly for 10 days. Children 20 mg/kg 8-hourly.

If you are treating invasive intestinal disease with drugs other than metronidazole or emetine, give him a 2-week course of chloroquine to prevent the development of hepatic lesions.

CAUTION ! The side-effects of emetine include nausea, diarrhoea, weakness, moderate hypotension, and alteration of the ECG. Serious cardiac effects are uncommon. Emetine is contraindicated in heart disease. Patients receiving emetine must stay in bed (they are usually so sick that they are happy to).

A SUMMARY OF TREATMENT METHODS for amoebiasis and its complications:

Amoebic dysentery without complications: metronidazole.

Amoebic liver abscess: metronidazole and dehydroemetine, or metronidazole and chloroquin, if he is seriously ill; aspiration or open drainage on the indications below.

Severe colitis wih perforation or suspected perforation: metronidazole, [pm]dehydroemetine, with tetracycline against secondary invaders. ''Drip and suck' him.

Spreading peritonitis: drugs, laparotomy and lavage.

Pericarditis (rare): drugs, aspiration and drainage.

Lung abscess (rare): drugs and postural drainage.