Abdominal Pain in an 8-Year-Old Male

J. Elliot Carter, MD; John J. Nelson, MD, MPH; Kelly N. Mizell, MD


Lab Med. 2007;38(6):357-360. 


Clinical History

Patient. 8-year-old Caucasian male.

Chief Complaint. Right lower quadrant abdominal pain.

History of Present Illness. Three-day history of worsening abdominal pain with nausea, vomiting, and low-grade fever. No history of diarrhea or lymphadenopathy.

Past Medical History. The patient had a history of routine childhood illnesses and asthma. Past surgical history consisted only of the placement of bilateral myringotomy tubes to treat chronic otitis media and a tonsillectomy at age 6.

Physical Exam Findings. The patient showed normal development for age and appeared well nourished. Physical examination was remarkable only for tenderness in the epigastric region and right lower quadrant.

Laboratory Findings. A complete blood count with differential and, due to the patient's abdominal symptoms, a stool rotavirus antigen test were performed ( Table 1 ).

Imaging Studies. Due to the patient's abdominal symptoms, radiographs of the abdomen were obtained. No abdominal masses were identified, and no evidence of volvulus, intussusception, or bowel obstruction was seen. Based on the clinical impression of acute appendicitis, the patient was taken to the operating room for emergency appendectomy.

Gross and Histopathologic Findings. The appendix received in the histopathology laboratory showed no gross evidence of abnormality. The specimen was serially sectioned, and microscopic examination of tissue sections showed evidence of acute appendicitis as well as the intraluminal structures shown in Figure 1.

Figure 1.

Microscopic sections (hematoxylin eosin [H&E] stain) of the patient's appendix illustrating A) cross sections of intraluminal nematodes (40×; arrows); B) higher magnification (200×) showing lateral cuticular projections or "alae" (arrows) diagnostic of E. vermicularis; C) gravid female nematode showing eggs in the reproductive tract (200×; arrows); and D) higher magnification (400×) of eggs of E. vermicularis.



  1. What are this patient's most striking clinical and laboratory findings?

  2. How do you explain these findings?

  3. What is the life cycle of this organism, and what are the structures identified in Figure 2A and 2B?

  4. What is the mode of transmission of infection?

  5. How is infection with this parasite diagnosed?

  6. What other nematodes are included in the differential diagnosis of an intestinal parasitosis?

  7. What are the treatment options for this patient?

  8. What is the usual outcome of this infection?

  9. What measures may prevent new infection and reinfection?

Figure 2.

Morphologic characteristics of an egg of Enterobius vermicularis illustrating its oval and flattened on one side appearance. Image provided courtesy of the Centers for Disease Control and Prevention Web site.

Possible Answers

1. The most striking initial clinical finding in this patient was abdominal pain of unknown etiology. In a pediatric patient, the differential diagnosis for abdominal pain is wide and includes bacterial, viral, or parasitic gastroenteritis, volvulus (twisting of the bowel with resulting ischemia), intussusception (telescoping of one section of the bowel into another), bowel obstruction, abdominal neoplasm such as lymphoma or Wilms' tumor, and acute appendicitis. Imaging studies may be useful in excluding volvulus, intussusception, and an abdominal mass; laboratory studies including bacterial cultures and identification of toxin production, viral assays, and ova-parasite examination of stool can help establish an infectious cause of the abdominal pain. Acute appendicitis, however, is a diagnosis of clinical exclusion and, when suspected, is a surgical emergency. The false-positive rate for clinical diagnosis of acute appendicitis with subsequent removal of a normal appendix is as high as 25%.[1] This false-positive rate is felt to be justified due to the morbidity and mortality associated with appendiceal perforation.

2. The abdominal pain seen in this patient was due to blockage of the appendiceal lumen with parasites, ischemia, and associated acute appendicitis. Figures 1A and 1B show the diagnostic morphologic characteristics of Enterobius vermicularis. Enterobius vermicularis, commonly known as pinworm, is one of the most common nematode parasites in humans, affecting as many as 42 million people in the United States alone.[2] Worldwide, an estimated 200 million people are infected. Enterobiasis is most common among children ages 5 to 14 and can be spread with particular efficiency in institutionalized patients and in the day care setting. Enterobiusvermicularis remains confined to the lumen of the gastrointestinal tract and, therefore, is not an invasive pathogen, but mechanical blockage of a portion of the appendix by adult worms may lead to ischemia and secondary appendicitis with perforation. In this patient, abdominal pain and an elevated white blood cell count with neutrophilia prompted appendectomy with subsequent histologic evidence supporting a diagnosis of acute appendicitis associated with E. vermicularis infection. Adult worms in the lumen of the appendix have also been seen incidentally at autopsy in patients with no prior clinical signs or symptoms and no histologic evidence of acute appendicitis. Appendicitis due to E. vermicularis appears to be an uncommon event with an incidence less than 2% in some pediatric studies.[3]

3. The life cycle of E. vermicularis is relatively uncomplicated (Figure 1). Adult pinworms live freely in the lumen of the large bowel and rectum where they mate. Female worms can produce as many as 10,000 fertilized, unembryonated eggs. At night, the female worms migrate through the anus and deposit their eggs on the perianal skin. The eggs embryonate and become infective shortly after deposition. The structures seen in Figures 1C and 1D are eggs seen within the reproductive tract of the adult female. The eggs of E. vermicularis are oval and flattened on one side (Figure 3). They measure approximately 55 × 25 μm (l × w).

Figure 3.

Life cycle of Enterobious vermicularis illustrating 1) deposition of eggs on perianal folds; 2) self-infection occurs by transferring infective eggs to the mouth with hands that have scratched the perianal area. Person-to-person transmission can also occur through handling of contaminated clothes or bed linens. Enterobiasis may also be acquired through surfaces in the environment contaminated with pinworm eggs (eg, curtains, carpeting). Some small number of eggs may become airborne and be inhaled. These would be swallowed and follow the same development as ingested eggs; 3) following ingestion of infective eggs, the larvae hatch in the small intestine while 4) the adults establish themselves in the colon. The time interval from ingestion of infective eggs to oviposition by the adult females is approximately 1 month. The life span of the adults is about 2 months; 5) gravid females migrate nocturnally outside the anus and oviposit while crawling on the skin of the perianal area. The larvae contained inside the eggs develop (the eggs become infective) in 4 to 6 hours under optimal conditions 1). Retroinfection, or the migration of newly hatched larvae from the anal skin back into the rectum, may occur but the frequency with which this happens is unknown. Figure provided courtesy of the Centers for Disease Control and Prevention Web site.

4. While many infections may be asymptomatic, the eggs of E. vermicularis deposited on the perianal skin can cause intense pruritis with excoriation. Eggs deposited under the fingernails of infected patients during scratching come in contact with the oral cavity, are swallowed, and mature in the small intestine for 4 to 6 weeks before reaching the colon. The eggs may also contaminate other surfaces through manual contact and spread infection to additional members of the household. While most cases of enterobiasis involve the gastrointestinal tract alone, rare cases of infection in female patients involving the vagina, fallopian tubes, ovary, and peritoneal cavity have been documented, apparently related to aberrant migration of the worms.[4]

5. Morphologic analysis of the adult worms and eggs, whether fresh or in histologic sections, is the mainstay of diagnosis. Anal swab or "Scotch tape" preparations may yield the typical morphology of eggs and occasionally adult worms characteristic of E. vermicularis. The adult female worm measures 8 to 13 mm in length and 0.3 to 0.6 mm in width. The smaller adult male measures 2 to 5 mm in length and 0.2 mm in width. In histologic sections, the adult worms have readily distinguishable lateral cuticular projections, the so-called "alae" or wings (Figure 1B). These projections are specific to E. vermicularis and are diagnostic of the parasite in tissue sections.

6. Common nematodes seen in the gastrointestinal tract include Ascaris lumbricoides, the hookworms Ancylostoma duodenale and Necatur americanus, Strongyloides stercoralis, Trichuris trichiura, and Trichinella spiralis. Morphologic characteristics of eggs, larvae, and adult worms help establish the correct diagnosis in cases of intestinal infection ( Table 2 ). Unlike the other common intestinal nematodes, E. vermicularis is not an invasive tissue parasite. It remains isolated to the lumen of the bowel and therefore causes no symptoms of anemia or systemic disease. The eosinophilia in the peripheral blood associated with tissue-invasive parasites is not seen with E. vermicularis infection.

7. Treatment of enterobiasis consists of the administration of anti-helminthic agents such as mebendazole or pyrantel pamoate.[5] These therapies eradicate the organism in up to 90% of cases, but reinfection is common. Several treatments may be required for long-term eradication. All members of a family may need treatment since almost any surface or object, including bedding, door knobs, or sinks, may become contaminated; the eggs of E. vermicularis are very resilient and can live on such surfaces for 2 to 3 weeks.

8. Infection with E. vermicularis poses few long-term health consequences. Infected patients may develop symptoms of appendicitis due to blockage of the lumen of the appendix by adult worms, but only in a minority of these cases is actual histologic evidence of acute appendicitis identified. Barring recurrence, infection is usually cured with adequate therapy.

9. Enterobius vermicularis is a ubiquitous inhabitant of soil and shows no gender, race, or socioeconomic predilection. Infection is not necessarily associated with poor hygiene or the cleanliness of surroundings. Treatment of infected individuals and household contacts helps eradicate all possible sources of infection. Additional preventative measures include thorough hand washing before cooking or eating, keeping fingernails short and clean, daily changing of bed linens of infected patients undergoing treatment, and washing linens in hot water as well as drying with heat to kill eggs.


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