Strongyloides colitis is a lethal mimic of ulcerative colitis: the key morphologic differential diagnosis

Summary

Strongyloides stercoralis colitis is a severe, but easily curable, form of strongyloidiasis that carries a high mortality rate if untreated. Autoinfection characteristic of Strongyloides stercoralis frequently makes the infection a life-long disease unless it is effectively treated. Our experience with 4 cases of Strongyloides colitis prompted us to assess the clinical outcome of the disease by literature review. In this case series, the misdiagnosis and resultant mortality rates of Strongyloides colitis are 52% and 39.1%, respectively. A low index of suspicion and morphologic resemblance to ulcerative colitis were the main sources of diagnostic error. Ulcerative colitis alone accounted for 38.5% of the erroneous diagnoses. Features of Strongyloides colitis that contrast with those of ulcerative colitis include (1) skip pattern of the inflammation, (2) distal attenuation of the disease, (3) eosinophil-rich infiltrates, (4) relative intact crypt architecture, and (5) frequent involvement of submucosa. We also found that history of steroid therapy, chronic colitis refractory to conventional immune-modifying management, and endoscopic finding of distal attenuation of the colitis are helpful clues. It is also our experience that if Strongyloides colitis is included in the differential diagnosis, the correct diagnosis can usually be made. Current therapy with ivermectin or albendazole is very effective at a cure rate greater than 98%. We believe that the misdiagnosis and mortality rates of this curable, but often, unnecessarily deadly, infectious disease are alarming and warrant efforts to increase the awareness of the disease.

Introduction

Strongyloidiasis is a helminth disease caused by the nematode parasite Strongyloides stercoralis. Typical life cycle begins with skin contact with infectious larvae in the soil. The larvae penetrate the skin, travel to the lung alveolar space via venous route, and reach the small intestine after being coughed up and swallowed. The adult female Strongyloides parasite produces the eggs that are hatched in the intestine, and the larvae are excreted in feces. The life cycle of Strongyloides stercoralis is also characterized by autoinfection by which the larvae may penetrate the intestinal mucosa and travel to the lung via venous route without leaving the human internal organs. As the result, the infection may persist for decades unless effectively treated [1], [2], [3], [4]. Although Strongyloides infection is relatively rare in the United States, its prevalence in southeastern Asia and among alcoholics in North America exceeds 20% [5], [6]. Strongyloidiasis is present worldwide. Genta [7] critically reviewed more than 100 epidemiologic studies on the prevalence of Strongyloides stercoralis among various populations on 5 continents. In addition to the endemic areas such as the Appalachian region and Louisiana in the United States, regions with large influx of tourists and emigrants from these endemic areas, southeastern Asia, and southern, eastern, and central Europe also have high incidence and prevalence of the disease [7]. The infection may remain clinically indolent. When the host is immune-compromised, hyperinfection syndrome (i.e., larvae overload in the lung and involvement of the rest of the gastrointestinal system) and disseminated strongyloidiasis (i.e., involvement of other organs) occur with a mortality rate near 90% [4], [8], [9].

Strongyloides colitis is a severe form of strongyloidiasis. It is typically a manifestation of the hyperinfection syndrome and disseminated strongyloidiasis with a high mortality rate if untreated [4], [10], [11], [12], [13], [14], [15], [16], [17]. Most reports of the hyperinfection syndrome have focused on clinical and radiologic findings. In fact, it appears that the initial diagnosis of Strongyloides enterocolitis is often not made by pathologists [15]. In a study of 75 cases of strongyloidiasis, Speare et al [9] found that only 27% of cases were diagnosed histologically, and that in 35% of these cases the diagnosis was made postmortem. It is, therefore, important to recognize its presentation and render a correct diagnosis. Although essential clinical features of strongyloidiasis have been well documented, reports on the clinical and pathologic features of Strongyloides colitis as a specific component of the hyperinfection syndrome are lacking. The morphologic changes of Strongyloides colitis often mimic idiopathic inflammatory bowel disease, particularly ulcerative colitis (UC) [12], [17]. A low index of suspicion for Strongyloides colitis because of its relative rarity and its morphologic resemblance to UC have been the major sources of diagnostic error in nearly all reported cases. Histologic features, especially those that contrast with features of UC, have not been established. Our experience with 2 other previously reported cases [16] and 2 new cases prompts us to assess the clinical outcome of the disease by literature review, with the focus on the clinical and morphologic features of Strongyloides colitis contrasting with those of UC.