A 60-year-old man presents with persistent pruritic eczema over his groin for one year. He has visited his primary care provider multiple times during this period, and been prescribed emollients, oral antihistamines, topical miconazole, and topical betamethasone. None of these relieved the rash.

His medical history is significant for type 2 diabetes diagnosed around five years ago. This was mild initially, but progressively worsened over time, necessitating insulin therapy around one and a half years ago.

On further close questioning, he recollects experiencing intermittent painful cracking of both corners of his mouth and soreness of his tongue over the last several months. He has also lost ~5 kg of weight over the last year, but assumed this was due to eliminating refined carbohydrates from his diet during that time period.

A complete blood count is significant for a hemoglobin of 10.5 mg/dL (normal:11-18). Peripheral smears reveal normocytic normochromic anemia. A reticulocyte count, serum iron studies, liver and renal profiles, a chest x-ray, and a c-reactive protein assay are all within normal parameters.