Pseudomelanosis duodeni is an uncommon endoscopic sign characterized by diffuse 
small black spots on the first and second portions of the duodenum. It occurs 
predominantly in female and elderly patients and is linked to chronic illnesses 
and related medications. Between 1988 and 1994, the authors saw eight patients 
with pseudomelanosis duodeni. To evaluate the nature of the pigments, special 
staining was performed in seven cases. Iron stain was strongly positive in three 
cases. Electron microscopy was performed in two cases. This revealed amorphous 
bodies within macrophage lysosomes in one case and angular crystals in another 
case. These tests suggest that in pseudomelanosis duodeni iron metabolism may be 
impaired and iron is pooled within macrophages.