U01.01.074 Vitamin B1

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Learning Objectives

  • Identify the four critical enzymes that require Thiamine Pyrophosphate (TPP).
  • Understand why glucose infusion can precipitate encephalopathy in deficient patients.
  • Distinguish between Dry and Wet Beriberi clinical presentations.
  • Recognize the neurological triad of Wernicke Encephalopathy and the permanent changes in Korsakoff Syndrome.

1. Biochemical Function

Thiamine (Vitamin B1) acts as the cofactor Thiamine Pyrophosphate (TPP). It is essential for carbohydrate metabolism and the HMP shunt.

Mnemonic: “Be APT”

  • Branched-chain ketoacid dehydrogenase
  • Alpha-Ketoglutarate dehydrogenase (TCA cycle)
  • Pyruvate dehydrogenase (Glycolysis to TCA)
  • Transketolase (HMP Shunt)

2. Deficiency Pathophysiology

Deficiency leads to impaired glucose breakdown and ATP depletion. Highly aerobic tissues like the brain and heart are affected first.

  • The “Glucose Rule”: In malnourished or alcoholic patients, give thiamine BEFORE dextrose. Infusing glucose first increases the demand for TPP, which can acutely deplete remaining stores and precipitate Wernicke Encephalopathy.
  • Diagnosis: Confirmed by observing an increase in RBC transketolase activity after adding Vitamin B1.

3. Clinical Disorders

Disorder Key Characteristics
Wernicke Encephalopathy Acute/Reversible. CorONA: Confusion, Ophthalmoplegia/Nystagmus, Ataxia.
Korsakoff Syndrome Chronic/Permanent. Confabulation, memory loss, personality changes. Damage to the medial dorsal nucleus of the thalamus and mammillary bodies.
Dry Beriberi Symmetric muscle wasting, polyneuropathy. (Ber1Ber1 = B1).
Wet Beriberi High-output cardiac failure and edema due to systemic vasodilation.

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