Perianal Pinworms (Enterobiasis)

This picture is of a 4-year-old girl’s perianal area showing numerous typical white thread pinworms.

The child’s mother stated the girl had been “pulling at her bottom” for 2 to 3 weeks. The mother thought she had been imitating her younger brother.

The clinical diagnosis was readily made by simple inspection of the perianal area. The patient and her household were treated with a single mebandazole (Vermox) chewable tablet, and a second in 2 weeks.

Pinworm infection is caused by the nematode Enterobius vermicularis and is the most common helminth infection in the United States. This worm is white, thready, and about 1 cm in length.

The pregnant female worm deposits up to 15,000 eggs perianally at night. Infection occurs by fecal-oral ingestion of the eggs, which mature in the gut. This worm inhabits the cecum, appendix, and adjacent ileum and colon.

The typical symptom of pinworm infestation is nocturnal perianal pruritis with resulting restless sleep. Symptoms parallel the severity of the infection.

Diagnosis is made by a history of perianal pruritis, most commonly in children although people of any age may be affected. If necessary, the diagnosis can be confirmed by microscopic examination of an adhesive glass slide or similar testing tool applied to the perianal area at night or early in the morning if no typical worms are present on visual perianal inspection.

Very infrequently, pinworms may be associated with appendicitis, chronic salpingitis, pelvic inflammatory disease, peritonitis, hepatitis, and ulceration of the small and large intestines.

Treatment is most commonly with oral mebendazole, 100 mg for all ages with a repeat dose in 2 weeks. Alternative treatments are:
o Albendazole, 400 mg by mouth for all ages, also repeated in 2 weeks,
or
o Pyrantel pamoate, 11 mg/kg by mouth, maximum 1 g in children age 2 years and older as a single dose.

Repeated treatments every 3 to 4 months may be necessary with repeated exposure, especially in institutionalized children.

The most effective prevention is good hand hygiene. Morning bathing and frequent washing of all bed-associated clothing and sheets may decrease autoinfection.¹

A couple of reminders for the clinician:
1. Visually inspect the symptomatic area. It’s amazing what one might find.
2. A microscopic sticky slide exam is unnecessary when you see the typical worms.

References:

Reference and for more information: 1. Kliegman RM, Stanton BF, St Geme III JW, et al. Nelson Texbook of Pediatrics. 19th ed. Elesevier Saunders. 2011: 1222.