Gastrointestinal: Enterobiasis

Abstract

Gastroenterologists who perform colonoscopy are likely to encounter occasional patients with small worms in the large bowel. The most common worm is Enterobius vermicularis (pinworm or threadworm). The infestation is acquired by direct person-to-person transmission, by autoinfection or by indirect spread associated with the handling of bed linen. Larvae in ingested eggs hatch in the jejunum, develop in the ileum and finally reside in the cecum and other parts of the colon. The female worm is 8–13 mm long while the male worm is only 2–5 mm long. The average lifespan of the worms is approximately 50 days. The only definite symptom attributed to enterobiasis is that of anal pruritis. This occurs when female worms actively pass out of the anus at night and lay sticky eggs over the perianal skin. Other clinical syndromes associated with enterobiasis may include vulvovaginitis in children and perhaps acute appendicitis. Enterobiasis is endemic throughout the world and particularly affects pre-school children, children in primary schools and children in institutions. Infestation rates may also increase in advanced age. Pinworms do not appear to cause inflammation in the large bowel and have not been associated with increases in blood eosinophils or serum IgE. The diagnosis can be made by the identification of worms at sigmoidoscopy or colonoscopy. However, the usual diagnostic test is the identification of eggs on a tape that is applied to the perianal area first thing in the morning. Several drugs are effective including mebendazole, albendazole and pyrantel pamoate. The patient illustrated below was a 90-year-old man who was admitted to hospital with abdominal pain and abdominal distension. Additional medical problems included hypertension, paroxysmal atrial fibrillation and chronic obstructive pulmonary disease. Blood tests revealed a mild normocytic anemia with a marked elevation of the erythrocyte sedimentation rate (108 mm/hr). A plain abdominal x-ray showed fecal loading in the colon. At colonoscopy, the only abnormality was thousands of small pinworms throughout the large bowel (Figure 1). Pinworms close to the anal canal are shown by retroflexion of the colonoscope in Figure 2. The appearance was typical of heavy infestation. His symptoms appeared to improve after treatment with albendazole.