PD represents a fine granular brown material inside the macrophage lysosomes in the lamina propria around the tips of the duodenal villi, detected by histochemical staining and electron microscopy. It has been postulated that this heterogeneous pigment may represent a deposit of melanin-like substances, hemosiderin, lipomelanin and lipofuscin[
6,7]. Even though iron (ferrous sulfide) is the main pigment compound, varying amounts of sulfur, calcium, potassium, aluminum, magnesium and silver can also be detected[
5,8]. The color of the pigment could represent various degrees of auto-oxidation of ferrous sulfide[
2,6].
The pathogenesis still remains unclear. It could be related to iron deposition secondary to intramucosal hemorrhage or impaired intramucosal iron transport after oral ferrous sulfate supplementation[
6,9]. Iron sulfide storage can also be a product of an acquired inherent defect in macrophage metabolism. In that regard, the pigment present in the duodenal mucosa has also been shown to be partially associated with impaired macrophage metabolism of drugs containing cyclic compounds such as phenols, indoles and skatoles[
8].
All four patients had undergone previous gastroduodenal endoscopy without any pathological findings, suggesting that this condition might be acquired rather than congenital, which is in keeping with previous reports[
5]. Importantly, it must be stressed that this entity might be identified histologically even before it becomes endoscopically visible, making it difficult to establish a temporal association between disease onset and endoscopic manifestation[
10].
In this report, all patients were female, with chronic renal failure, and taking antihypertensive drugs. Of note, only two patients were taking oral iron supplements. The biopsy specimens were positive for hematoxylin and eosin and Masson-Fontana stains but not reactive for Pearl’s stain, suggesting a melanin-like compound. Although Pearl’s stain is a classic method for demonstrating iron in tissues, there is a possibility of a false-negative reaction if an iron oxide compound is present instead of iron sulfide[
11,12].
In conclusion, these findings suggest that the duodenal involvement can occur in the absence of a history of oral iron supplementation. Importantly, although the long-term clinical impact of these depositions remains unclear, these endoscopic findings still do not require any specific treatment or recommended follow-up.