Reversible morphological changes of rectal mucosa in vitamin B12 deficiency

The histomorphology of the rectal mucosa in a case with pernicious anemia was studied before and after treatment with vitamin B12. In the vitamin-deficient state the mucosa exhibits a decrease in the number of mitoses and an increase in the nuclear diameter and nuclear-cytoplasmic ratio. These changes return to normal after vitamin administration. The reversible morphological alterations may serve as an example for the importance of vitamin B12 in maintaining the structure and possible the function of the rectal mucosa.