A 10-year-old boy was admitted to the hospital for an allogeneic BMT. He was diagnosed with non-Hodgkin's lymphoma 6 years previously, and the therapeutic procedure for the lymphoma was completed in October 2003. His disease relapsed in August 2007, and he was re-diagnosed with acute lymphoblastic leukemia based on bone marrow aspiration and biopsy. Complete remission was achieved, and an allogeneic BMT was planned. The patient underwent total body irradiation and cyclophosphamide for the conditioning; tacrolimus and methotrexate were used for the prophylaxis of graft versus host disease (GVHD) and he was provided with an immunosuppressant. His oral intake was low, and he was solely dependent on a commercially available total parenteral nutrition product. His neutrophils were engrafted on D+11. On D+11, he complained of dizziness and headache, but those symptoms quickly subsided. On D+23, vertigo and nystagmus developed, but his mental status was alert, and he did not show sensory or motor changes in the extremities. Three days later, he presented diplopia and esotropia, and complained of difficulty in closing his eyes. Brain magnetic resonance imaging (MRI) was performed; we initially considered the toxicity of metronidazole or immunosuppressant (Fig. 1A). Metronidazole administration was discontinued. On D+30, he started to complain of dyspnea, and suffered simple and complex partial seizures one day later, which composed of lip smacking and clonic movements of the left shoulder. Apnea and bradycardia developed on D+33 and the patient was transferred to the intensive care unit for ventilator care. His mental status became semicomatose. The follow-up brain CT and clinical progress since metronidazole discontinuation suggested Wernicke's encephalopathy (Fig. 1B). The blood level of thiamine was low (0.2 U/L; reference range 2-7 U/L). Thiamine was subsequently administered. Over the following two weeks, his mental status gradually, but not completely, improved. On D+50, he died of septic shock after suffering pneumonia, which developed after microaspiration.

A 12-year-old boy underwent allogeneic BMT. He was diagnosed with Philadelphia chromosome positive acute lymphoblastic leukemia. After induction and consolidation chemotherapy, the patient underwent the BMT. He received total body irradiation and cyclophosphamide administration for the conditioning procedure. Cyclosporine and methotrexate were used for the prevention of GVHD. He suffered from severe nausea and vomiting and could not orally take nutrition. On D+12, neutrophils were engrafted stably. After the conditioning procedure was initiated, the patient was solely dependent on a commercially available parenteral nutrition product. His general activity was slightly poor. He responded slowly to requests, but his mental status was alert. On D+22, he seemed slightly drowsy and confused, and complained of marked dizziness. He could not walk to toilet and intermittently exhibited intention tremors on both hands. Lid nystagmus was observed, but there was no eyeball nystagmus. There were no sensory or motor changes. MRI taken on D+24 revealed increased signal intensity on the dorsal pons on T1 weighted images (Fig. 2A). He was suspected of having Wernicke's encephalopathy, and thiamine 100 mg was given for 7 days. Twenty-four hours after thiamine infusion began, his dizziness and mental status were remarkably improved, and all his symptoms cleared four days later (Fig. 2B).