Pseudomelanosis duodeni is seen endoscopically as dark spots in the duodenal 
mucosa and is generally considered to be local deposition of iron from oral iron 
intake. However, pseudomelanosis duodeni may be identified histologically even 
before it becomes endoscopically evident; iron stainability within the mucosa is 
uneven and unpredictable, and multiple clinical conditions other than oral iron 
intake may be associated. We reviewed 17 adult patients with histologically 
detected pseudomelanosis duodeni, their endoscopic appearances, iron 
stainability, and clinical findings including oral iron and drug intake. Only 
6/17 (35 %) had endoscopically apparent dark spots. Perl's iron stain was 
entirely positive in 18 %, partially positive in 64 %, and negative in 18 % of 
cases. History of oral iron was present in 76 % of patients, but other clinical 
conditions consistently associated were hypertension in 88 %, end stage renal 
disease in 59 %, and diabetes mellitus in 35 % of patients.