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Under the Microscope: How would you diagnose this case?

A 57-year-old man who carries a diagnosis of ulcerative colitis presents for colonoscopy. Histologic sections from the right colon show chronic and active inflammation with increased eosinophils, along with occasional structures like the one pictured below (Image 1, black arrow). What is your diagnosis?

  1. Ulcerative colitis with foreign body.
  2. Strongyloides stercoralis colitis.
  3. Crohn’s disease with foreign body.
  4. Infectious (bacterial) colitis.

Image 1


Answer: B. Strongyloides stercoralis colitis.

Infection by Strongyloides stercoralis, a nematode frequently acquired through bare feet walking on infested soil, is often considered to be primarily an infection of soldiers abroad and adventurous travelers. While many sufferers acquire their infections in tropical and subtropical locales, there are also endemic areas in the Southeastern United States, particularly in the Appalachian region.1 In addition, the nature of the Strongyloides life cycle permits the organism to persist within its host for many years, making a history of travel to endemic areas a distant memory to many patients.

The case of Strongyloides stercoralis colitis depicted in Image 1 (which shows a larval form) was recently diagnosed at Miraca Life Sciences. Regarding the other answer choices,Strongyloides colitis may indeed share histologic features with IBD (discussed below); infectious (bacterial) colitis would show active inflammation without well-developed chronic changes and would not contain larvae. The infected patient in this case, a 57-year-old man with no reported history of travel outside of the United States, had carried a diagnosis of ulcerative colitis for over eight years. Part of his regular treatment regimen included corticosteroids. He presented for routine surveillance colonoscopy, which showed erythema in the right colon. Histologic sections from a biopsy of the erythematous area showed some features consistent with active, partially treated ulcerative colitis, including mild architectural distortion, a lymphoplasmacytic lamina proprial infiltrate with plentiful eosinophils and areas of basal plasmacytosis, active inflammation, and reactive epithelial and stromal changes (Image 2).

Image 2: Chronic and active inflammation with abundant eosinophils.


Importantly, however, the eosinophils in the lamina propria were greater in number and concentration than is typical for ulcerative colitis. Careful examination of the tissue revealed organisms within the lamina propria as well as within the crypt epithelium (Image 3, arrows).

Image 3: Strongyloides spp, larval forms.


Since Strongyloides colitis and ulcerative colitis share many clinical, colonoscopic, and histologic features, and since the organisms can easily be overlooked (especially if one has little experience with this disease) in tissue examination, it is not surprising that this patient’s colitis had previously been diagnosed as inflammatory bowel disease. A retrospective review by Qu et al describes a series of 25 cases of Strongyloides colitis with 5 of those cases originally erroneously diagnosed and subsequently treated as ulcerative colitis.2 In the absence of identifiable organisms, several important but subtle features can assist in distinguishing ulcerative colitis from Strongyloides colitis. Attenuation of disease in the distal colon and rectum may be seen in Strongyloides infection, while ulcerative colitis will often show florid distal involvement (in the absence of topical treatment effects such as enemas). While ulcerative colitis characteristically extends without areas of sparing, spared areas are common in Strongyloides colitis.

These latter, disease-distribution-related features may prompt us to wonder whetherStrongyloides colitis is attempting to resemble Crohn’s disease, and in truth Strongyloidesdoes a good job of impersonating Crohn’s as well as ulcerative colitis, with its minimal or mild architectural distortion, the frequent presence of aphthoid ulcers, and inflammation extending to submucosal depths. (In Qu et al’s review, Crohn’s disease represented 7.7% of misdiagnoses of Strongyloides). Fortunately, there are also a few characteristics ofStrongyloides that can help avoid a misdiagnosis of Crohn’s, including a relative paucity of true crypt abscesses in Strongyloides, more frequent eosinophilic abscesses inStrongyloides, and the usual lack of basal plasmacytosis in Strongyloides. Clinically, a patient with Strongyloides may have prominent peripheral eosinophilia (but this is by no means a universal feature of chronic strongyloidiasis), an exacerbation of disease symptoms upon starting steroid therapy, and respiratory signs or symptoms.

Figure 1. Disseminated Strongyloidiasis. (Figure courtesy of Robert M. Genta, MD).


It is important to be aware of this organism, as well as of other rare entities, when evaluating a biopsy of an inflammatory process. Miraca Life Sciences GI pathologists encounter such diseases with sufficient frequency that unusual infectious etiologies are always part of their working differential diagnosis and therefore, much less likely to be missed. Such experience can be potentially life-saving: in immunocompromised hosts, particularly patients on long-term corticosteroid therapy (a mainstay of inflammatory bowel disease treatment), the host-parasite balance may be altered, with large numbers of larvae undergoing the autoinfectious cycle. This is known as hyperinfection, and is characterized by a massive invasion of larvae in the lungs, where hemorrhage and Gram-negative pneumonia develop. In these patients,S. stercoralis can also migrate to other parts of the body, including meninges, brain, and kidneys (disseminated strongyloidiasis; see Figure 1). Both these conditions, unless recognized very early, carry a 100% mortality rate.2

Fortunately, an effective therapy is available for Strongyloides infection, but early treatment of hyperinfection is paramount. Awareness of uncommon entities such as this, as well as diligent, thorough collaboration between clinician and pathologist during the diagnostic process, is essential in arriving at the correct diagnosis, thus allowing the selection of the proper therapy for our patients.


  1. Genta RM. Global prevalence of strongyloidiasis: critical review with epidemiologic insights into the prevention of disseminated disease. Rev Infect Dis. 1989;11:755–767.
  2. Qu Z, Kundu UR, Abadeer RA, Wanger A. Strongyloides colitis is a lethal mimic of ulcerative colitis: the key morphologic differential diagnosis. Hum Pathol. 2009 Apr;40(4):572-7. Epub 2009 Jan 13.
  3. Genta RM. Dysregulation of strongyloidiasis: a new hypothesis. Clin Microbiol Rev. 1992 Oct;5(4):345-55. Review.
  4. Genta RM, Weesner R, Douce RW, Huitger-O’Connor T, Walzer PD. Strongyloidiasis in US veterans of the Vietnam and other wars. JAMA. 1987 Jul 3;258(1):49-52.