Surprising finding on colonoscopy
While looking for the cause of our patient’s intermittent rectal bleeding, we discovered something else entirely.
The Scotch tape test clinches the diagnosis
The “Scotch tape test” is the most commonly used diagnostic test for pinworm infection. A clinician applies a piece of clear cellulose acetate tape to the unwashed perianal skin in the morning on 3 separate occasions. He or she then applies the tape to glass slides and sends them to the lab.1
The characteristic findings are long, oval, colorless eggs, 50 to 60 micrometers in length, which are flat on one side (FIGURE 2).
The patient’s perianal area may also be examined with a flashlight late at night or early in the morning; occasionally glistening adult worms are found. Stool samples are often negative for worms and eggs; thus, stool examination is rarely helpful.
Tx: Antiparasitics for patients and others in household
Patients with pinworm infection are initially treated with 1 dose of oral mebendazole (100 mg), albendazole (400 mg), or pyrantel pamoate (11 mg/kg, maximum dose 1 g) (strength of recommendation [SOR] B).8-10 Some sources suggest pregnant patients be treated with pyrantel pamoate (a Category C drug in pregnancy), whereas others recommend deferring treatment until after delivery, as harm to the fetus by pinworm infection has not been reported in the literature (SOR C).1,3,11
Regardless of which antiparasitic is used, treatment should be repeated after 10 to 14 days, given the high relapse rate. Repeat treatment is especially important with mebendazole, which is active only against worms—not eggs.
Household members should also be treated, as the infection is readily transmitted and others may have asymptomatic infection (SOR B).1,3,12 In order to prevent reinoculation or spread of the infection, patients should practice good hand hygiene, including trimming their fingernails. The patient and family members should wash all sheets, clothes, and towels. Pets need not be treated, as they cannot serve as reservoirs.1,3
A good outcome. We treated the patient with mebendazole 100 mg once and repeated treatment 10 days later. We taught the patient how to prevent reinfection, and we asked him to follow-up at the clinic, as needed.
