General Medical Information

Pinworms

Wilberto Nieves-Neira
Bhagirath Majmudar
Ira R. Horowitz

Enterobius vermicularis (pinworm) should be suspected in girls who present with vulvar and/or perianal itching as the main symptom. Nocturnal exacerbation of the pruritus increases the degree of suspicion. This occurs as the female worm emerges from the anus to deposit the eggs on the external skin. As many as 20% of girls infested with pinworms develop an associated vulvitis. Rarely, a female worm may become trapped in the vagina and cause primary vaginitis. Pinworms are a cause of persistent or recurrent vulvovaginitis. Pinworm infestation has been associated with increased incidence of E. coli cultures from the introitus and recurrent urinary tract infections. Usually there is perianal and vulvar erythema. Because the patient often scratches, vulvar skin abrasions are likely to be present. Diagnosis is based on the direct observation of the worm or more commonly its eggs. The Scotch tape test usually is effective in establishing the diagnosis. Stool samples for ova and parasites usually do not detect pinworm ova. The most common treatment is mebendazole as a single 100-mg tablet. For patients with vulvovaginitis, a second course of treatment may be advisable to cover any possible eggs in the vaginal introitus. Other regimens include pyrantel pamoate 11 mg/kg up to 1 g or pyrvinium pamoate 5 mg/kg up to 350 mg. Vulvar granulomas secondary to E. vermicularis eggs have been reported.