Oral diagnosis of vitamin B12 deficiency due to long-term metformin treatment: a case report

Metformin is the first line treatment for type 2 diabetes. It is also indicated in patients with insulinresistant type 1 diabetes. It has several benefic effects on carbohydrate metabolism, weight loss and vascular protection. However, it can also cause serious adverse reactions such as the risk of anemia associated with long term use. It has been reported that long-term metformin use might reduce serum vitamin B12 levels. Oral signs combining Hunter glossitis and stomatodynia may be revelatory and lead to early diagnosis of vitamin B12 deficiency. We here report the case of a female patient who had had these oral signs for 2 years and whose laboratory tests revealed normocytic anemia with iron and vitamin B12 deficiency. The diagnosis of vitamin B12 deficiency due to long-term metformin was suspected while excluding other potential causes. Intramuscular hydroxocobalamin injection associated with oral iron led to the normalization of serum levels and to the disappearance of clinical signs. The patient was referred to a specialized center for further etiological assessment. This clinical case highlights the essential role of dentists in early diagnosis of vitamin B12 deficiency and the prevention of its progression, which can be dramatic in the case of late discovery.