Relapses after interruption of cyanocobalamin therapy in patients with pernicious anemia.

One or more episodes of recurrent megaloblastic anemia occurred in 36 (10.8 percent) of 333 patients with pernicious anemia following interruption of therapy. Treatment had most commonly been discontinued by patients because they felt well, or by physicians due to error. Thirty-five episodes of recurrent cobalamin deficiency were analyzed in detail. In the 24 patients in whom the exact date of cessation of therapy was recorded, the mean interval before relapse was diagnosed was 64.5 months (range 21 to 123 months). Recurrence manifested as macrocytosis in the absence of anemia occurred earlier (mean, 49.2 months) than that associated with anemia (73.1 months). A weak correlation was apparent between the amount of previous cyanocobalamin treatment and time to relapse. One third of relapses were unrecognized and left untreated for more than two years, while usually slow hematologic progression occurred. Recurrences of cobalamin deficiency in individual patients exhibited mimetic features. Further study is necessary to establish the optimal dosage and frequency of maintenance therapy in pernicious anemia.