Thyrotoxicosis is a hypermetabolic state in which there is increased utilization of thiamine. Thiamine deficiency has been observed in association with hyperthyroidism. Several studies documented that thiamine treatment could improve signs and symptoms of congestive heart failure, or even improve left ventricular ejection fraction in patients without thyrotoxicosis. This pilot study aims to evaluate prevalence of thiamine deficiency and assess improvement of cardiovascular function after receiving thiamine supplement in thyrotoxic patients.

The prevalence of thiamine or vitamin B1 deficiency has been documented in 21-98% of patients with heart failure. Thiamine has multiple effects on the cardiovascular system. It has important hemodynamic effects on the circulatory system as well as direct positive pharmacologic effects on the heart. Thiamine deficiency has been shown to cause cardiac hypertrophy, depressed cardiac contractility, and dysrhythmias. Thiamine is of particular interest in the management of heart failure for several reasons. Heart failure is a disease of the elderly whose micronutrient status is in need of attention. Heart failure patients tend to have inadequate nutrient intake, which has been associated with thiamine deficiency. Use of loop diuretic is associated with the loss of water-soluble vitamins, including thiamine. Several studies have examined the role of thiamine supplementation in patients with heart failure. Clinical trials in patients with congestive heart failure have shown that thiamine supplementation increases the systolic, diastolic, and central venous pressures, with a decline in heart rate and increase in left ventricular ejection fraction (LVEF). Thiamine acts as a vasodilator and reduces the afterload on the heart, thus improving cardiac function. Thiamine has also been reported to increase diuresis and natriuresis in patients with heart failure receiving diuretics.

Thyrotoxicosis considerably increases the demand for thiamine. In vivo study in a rat model demonstrated that thyroid hormones have a direct influence on mitochondria which is the main source of energy. Thiamine in its various forms functions as an important coenzyme for macronutrient oxidation and the production of adenosine triphosphate. Thiamine pyrophosphate works in several oxidative decarboxylation reactions and is a catalyst in the reactions of Krebs cycle. Therefore, thiamine seems to decrease in the case of an increased tissue metabolism. In the previous case reports, they described the possible association between thyrotoxicosis and thiamine deficiency in patients manifested as Wernicke-Korsakoff syndrome.

Despite lack of the evidence of benefit of thiamine therapy in patients with severe thyrotoxicosis or thyroid storm, some experts recommended thiamine in conjunction with other supportive treatment. We aimed to investigate the effect of thiamine on cardiac function in patients with severe thyrotoxicosis in a prospective, randomized, open, blinded end-point study using echocardiographic as well as clinical endpoints.

Inclusion Criteria:

• Hospitalized patients with severe thyrotoxicosis
• Thyrotoxic patients with cardiovascular involvement e.g. heart rate > 90/min, atrial fibrillation or congestive heart failure
• Agree to participate by written informed consent

Exclusion Criteria:

• Previously treated with thiamine within 1 month before the enrollment
• End-stage renal disease
• Alcoholism
• Pregnant or lactating women
• Post gastric bypass surgery