Pseudomelanosis duodeni is a benign finding caused by the accumulation of iron and melanin in mucosal macrophages, which typically incorporate sulfur into the granules, causing positive reaction with both iron and Fontana-Masson stains (1). The condition most frequently affects those with AIDS, individuals on maintenance hemodialysis, and some case reports link it to systemic hypertension (2). It may be seen grossly during endoscopy as brown or black spots on the duodenal mucosa, typically in the latter portions (3). Although most patients have reported abdominal discomfort anemia in association, it is not clear that pseudomelanosis is causal for these symptoms, and is likely discovered only as a result of their creating an indication for endoscopy. Patients on parenteral iron therapy may also accumulate iron deposits in macrophages in similar fashion, via mucosal iron deposition.
The condition may cause superficial confusion with melanoma, which is most frequently metastatic. Melanomas will usually create a mass, or at the very least, show an infiltrative pattern through the bowel mucosa, features which are absent here. In addition, the cells are usually more atypical than the relatively bland appearing macrophages with abundant cytoplasm and inconspicuous nucleoli present in the current case. If melanoma is at all a concern, immunohistochemistry for melanoma markers such as S100, tyrosinase A, and HMB-45 can be performed, and should be negative in pigmented cells in pseudomelanosis.
One of the major differential diagnoses of pseudomelanosis coli is hemochromatosis. Hemochromatosis typically shows iron deposition throughout the mucosa, and importantly, iron staining will show increased uptake in the overlying epithelial cells and around vessels, features which are not present here. Genetic analysis for mutations in the HFE gene can be performed, although mutations in this gene are not always completely penetrant, and genotype may not correlate well with the patient's phenotype (4).
One can certainly argue that this case best represents "pseudomelanosis jejuni," given the endoscopist's report of the biopsy site and absence of Brunner's glands to definitively identify duodenum. However, the distinction between distal duodenum and proximal jejunum can be difficult to identify endoscopically, and the biopsy may still represent distal duodenum. Further, while pseudomelanosis duodeni has been described, pseudomelanosis jejuni has, to our knowledge, not been, although an identical process is clearly active in this case. To avoid clinical confusion, a diagnosis of "pseudomelanosis duodeni" was rendered instead.
Contributed by Gerard J Oakley III MD and Alyssa Krasinskas, MD