An odd looking ulcer

This patient was undergoing a gastroscopy for iron deficiency anaemia. A small ulcer is found in D2.
WHAT IS THE LIKELY AETIOLOGY?

■ Peptic ulcer

Statistically probably most likely diagnosis

■ Pill ulcer

Yes, but what pill?

■ Adenoma

Often do appear depressed here (IIc lesions) but not in this case

■ Early cancer

Early duodenal cancer usually look like sessile adenomas or, less commonly like indurated ulcerated lesions

explanation

If it wasn't for the somewhat odd, elongated appearance of the ulcer, it wouldn't seem odd. However, the only clue to the aetiology is that yellowish appearance.  You may be familiar with 'iron pill gastritis' but can you get iron pill duodenitis?  Yes you can!  It has even been reported in the hypopharynx and the oesophagus. Those dark spots on the histology slides are crystalline iron deposits are easy to spot for the pathologists. 

Of course, ferrous sulphate (Fe2+)  tablets is the non-toxic form of iron (naturally).  However, the tablets can produce mucosal inflammation if the iron becomes oxidised to  Ferric iron (Fe3+). You may remember from medical school that most dietary nonheme iron is in the toxic, oxidized form of ferric iron (Fe3+).  To absorb iron it first needs to be reduced, in the presence of acid, to ferrous iron (Fe2+).  After this, the iron is easily transported across the enterocytes via a divalent metal-ion transporter 1 (DMT1) protein.  Here is a link to an open access article if you want to brush up on iron absorption. 

Naturally, the treatment is to change to the liquid form of iron supplement which is much less toxic to the mucosa than solid iron tablets.