Most thiamine deficiency in the United States is due to alcohol use disorder, with poor dietary intake of thiamine and impaired thiamine absorption, metabolism, and storage. It is also associated with malabsorption (eg, following bariatric surgery), dialysis, and other causes of chronic protein–calorie undernutrition. Thiamine depletion can be precipitated when patients with low thiamine are given a large carbohydrate load, such as an intravenous dextrose infusion.
Early manifestations of thiamine deficiency include anorexia, muscle cramps, paresthesia, and irritability. Advanced deficiency primarily affects the cardiovascular system (“wet beriberi”) or the nervous system (“dry beriberi”). Wet beriberi occurs in thiamine deficiency accompanied by severe physical exertion and high carbohydrate intake. Dry beriberi occurs in thiamine deficiency accompanied by inactivity and low-calorie intake.
Wet beriberi is characterized by marked peripheral vasodilation resulting in high-output heart failure with dyspnea, tachycardia, cardiomegaly, pulmonary edema, and peripheral edema with warm extremities mimicking cellulitis.
Dry beriberi involves both the peripheral and the CNS. Peripheral nerve involvement is typically a symmetric motor and sensory neuropathy with pain, paresthesia, and loss of reflexes. Legs are affected more than arms. CNS involvement results in Wernicke-Korsakoff syndrome. Wernicke encephalopathy consists of nystagmus progressing to ophthalmoplegia, truncal ataxia, and confusion. Korsakoff syndrome includes amnesia, confabulation, and impaired learning.
In most instances, the clinical response to empiric thiamine therapy is used to support a diagnosis of thiamine deficiency. The most commonly used biochemical tests measure thiamine concentration directly, while other assays measure erythrocyte transketolase activity and urinary thiamine excretion. Normal thiamine values typically range from 70 nmol/L to 180 nmol/L. A transketolase activity coefficient greater than 15–20% also suggests thiamine deficiency.
Thiamine deficiency is treated with large parenteral doses of thiamine. Fifty to 100 mg/day is initially administered intravenously, followed by daily oral doses of 5–10 mg/day. All patients should simultaneously receive therapeutic doses of other water-soluble vitamins. Treatment results in complete resolution in one-fourth of patients immediately and another one-fourth over days, but half have only partial or no benefit.
Patients with signs of dry beriberi or Wernicke-Korsakoff syndrome should be referred to a neurologist. Patients with signs of wet beriberi should be referred to a cardiologist.