B vitamins are essential for the functioning of the nervous system. Vitamin B1 (thiamine) deficiency is associated with neuropsychiatric syndromes such as Wernicke's encephalopathy (WE), which, if untreated, has an estimated mortality of 17–20%. Although the prevalence of thiamine deficiency in the general population is difficult to estimate, it is being increasingly recognized in oncology, especially in the inpatient setting. We describe three cases of thiamine deficiency (TD) in the outpatient psychiatric oncology setting.

Retrospective chart review of three adult patients, who were seen in the psychiatric oncology clinic and found to have TD on laboratory testing, was done. Patient, disease, and thiamine treatment-related information were obtained, and descriptive statistics were used to analyze the data.

The average age was 59 years, mean body mass index (BMI) was 22.00 ± 4.58 (mean ± SD), and mean thiamine level was 59.10 ± 7.69 that ranged from 45 to 68 nmol/L (normal thiamine level reference: 70–180 nmol/L). None of the patients had brain imaging nor cerebrospinal fluid analysis. Risk factors such as unbalanced nutrition, prior GI surgery, renal disease, and chemotherapy were noted.

TD can have a multifactorial etiology in oncology. Identification of TD in both inpatient and outpatient setting is important. Our report highlights how early identification of TD in the outpatient setting can help prevent further clinical progression.

Although thiamine deficiency (TD) and Wernicke encephalopathy (WE) are not rare in cancer patients, the cases reported to date developed TD and/or WE after treatment had started.

From a series of cancer patients, we report a patient diagnosed with TD without the typical clinical symptoms of WE at the preoperative psychiatric examination.

A 43-year-old woman with ovarian cancer was referred by her oncologist to the psycho-oncology outpatient clinic for preoperative psychiatric evaluation. Her tumor had been growing rapidly before the referral. Although she did not develop delirium, cerebellar signs, or eye symptoms, we suspected she might have developed TD because of her 2-month loss of appetite as the storage capacity of thiamine in the body is approximately 18 days. The diagnosis of TD was supported by abnormally low serum thiamine levels.

Cancer therapists need to be aware that thiamine deficiency may occur even before the start of cancer treatment. In cases with a loss of appetite of more than 2 weeks’ duration, in particular, thiamine deficiency should be considered if the tumor is rapidly increasing, regardless of the presence or absence of delirium.

Wernicke encephalopathy (WE) is a neuropsychiatric disorder caused by thiamine deficiency. Several reports of WE in cancer patients are known. WE is sometimes overlooked because most patients do not exhibit its typical symptoms (e.g., delirium, ataxia, ocular palsy). If delirium is not present, a diagnosis of WE is difficult because delirium is the hallmark symptom of WE.

Taken from a series on WE in cancer, we report two patients who developed WE without delirium during periodic psycho-oncology outpatient visits.

Case 1. A 61-year-old woman with non-Hodgkin lymphoma who was periodically attending a psycho-oncology outpatient clinic developed an unsteady gait. WE was suspected because she also developed appetite loss for two weeks, and we could find no other laboratory findings to explain her unsteady gait. Our diagnosis was supported by abnormal serum thiamine and disappearance of the gait disturbance after intravenous thiamine administration. Case 2. A 50-year-old woman with breast carcinoma with bone metastasis developed an unsteady gait. WE was suspected because she also developed loss of appetite for two weeks, and no other laboratory findings could explain her unsteady gait. The diagnosis was supported by abnormal serum thiamine and disappearance of the gait disturbance after administration of intravenous thiamine.

Our report emphasizes the importance of being aware of WE, even when patients do not present with delirium. The presence of loss of appetite for more than two weeks may be the key to a diagnosis of WE.