Acute Mental Disorder Caused by Vitamin B12 Deficiency Eight Years After Total Gastrectomy

Vitamin B12 deficiency can cause a variety of diseases. The most common disease is macrocytic anemia, but it has also been found to be a cause of psychiatric disorders. The causes of deficiency are varied, and diagnosis is often difficult. Here, we report a patient who developed mental disorders due to vitamin B12 deficiency after total gastrectomy. A 37-year-old female, eight years after total gastrectomy, was withdrawn at her workplace, talking and acting abnormally. The family had seen unusual behavior for three days. The patient had no particular history of mental illness. The possibility of herpes encephalitis was suspected, and the patient was referred to our hospital, but there were no specific findings in the head on imaging examination. Blood tests showed no macrocytic anemia. Spinal fluid cytology and electroencephalography showed no specific findings, and herpes DNA was negative. Metabolic factors such as vitamin deficiency were considered, and intravenous vitamin replacement therapy was initiated. The psychiatric symptoms improved rapidly after vitamin B12 supplementation was started. On the fifth day of her hospitalization, it was discovered that her vitamin B12 level at the time of admission was extremely low. Typically, vitamin B12 deficiency is associated with macrocytic anemia, but in this patient, serum iron was also decreased, indicating a mixed anemia, making the diagnosis difficult. The patient had undergone a total gastrectomy for gastric cancer eight years ago, and the psychiatric symptoms were thought to be due to impaired vitamin B12 absorption caused by intrinsic factor deficiency. Since then, oral replacement therapy and intramuscular injection have been continued without recurrence of symptoms. Disturbances of consciousness may have many causes, but when there is a history of gastrectomy, we should also consider vitamin B12 deficiency when examining patients.