Microbiology Case Study: How to “Pin” a Diagnosis

Case History

A 7 year old female presented to the emergency department with left sided abdominal pain and a temperature of 103 degrees Fahrenheit. Labs drawn showed mild leukocytosis with a CT scan suggestive of acute appendicitis. The patient underwent uncomplicated appendectomy with no complication. Gross examination of the appendix revealed an unremarkable, non-perforated serosa and a fecalith within the lumen. Representative tissue sections submitted for microscopic analysis per grossing policy. The findings below led to the submission of the entire appendix to be evaluated.

Figure 1. Low power image of an appendix demonstrating mild acute inflammation, lymphoid hyperplasia and congestion.

Figure 2. High power image, Cross-section of an adult female E. vermicularis from the same specimen shown in Figure 1. Adherent to the appendiceal surface. Note the presence of the alae (blue arrow), and the presence of almond shaped eggs (red arrow).

Discussion

The nematode Enterobius vermicularis, widely known as the human pinworm, is one of the most common parasitic worm infections today in the United States, infecting approximately 40 million people. The patient population is often children who are infected via fecal-oral transmission, with autoinfection being common. Humans are the only known host of this nematode. Once E. vermicularis embryonated oocytes are ingested, the larvae hatch and inhabit the gastrointestinal system. At night, the larvae migrate down to the anus, lay their eggs, and the cycle recurs.

The clinical presentation can be asymptomatic or can present with perianal pruritus at night, which can be explained via the life cycle of the parasite as stated above. The method of choice for diagnosing E. Vermicularis is microscopic examination of the eggs via cellulose tape slide test. A piece of scotch tape collects the eggs near the perianal area of the patient, which is then used for analysis and identification of the eggs. Microscopically, E. Vermicularis can be identified by the spines or ‘alas’ on the surface with oval shaped, thick capsuled oocytes within, seen in figure 2. To improve the sensitivity of the scotch tape test, it is best to do this test in the early morning, when there is an increased chance of sampling the eggs.

Rarely, is this worm associated with any severe symptoms but patients can present with abdominal pain, suggesting intestinal obstruction, extra intestinal manifestations like vulvovaginitis, or appendicitis. The relationship between E. Vermicularis and appendicitis is up for debate as to whether there is a causative relationship or if it is an incidental finding seen within appendicitis. Regardless of the relationship, once a diagnosis of Enterobius vermicularis is made, treatment with an anthelmintic needs to be given to the patient, such as Albendazole or Pyrantel Pamoate. In addition, treatment for everyone in the household needs to be considered in confirmed cases of infection.

Routine surgical specimens, such as appendices, can perhaps be overlooked once acute inflammation is noted. It is important to be able to identify organisms, such as pinworms, on such specimens to get the patient the appropriate treatment.

References

-Alexandra Medeiros, MD, is a first year anatomic and clinical pathology resident at Medical College of Georgia at Augusta University. Her academic interests include Forensic pathology, and surgical pathology.