vitamin B1

Thiamine is converted to its active form, thiamine pyrophosphate (TPP), which acts as a cofactor for several critical dehydrogenase/decarboxylation reactions: pyruvate dehydrogenase (links glycolysis to TCA cycle), alpha-ketoglutarate dehydrogenase (TCA cycle), transketolase (pentose phosphate pathway), and branched-chain ketoacid dehydrogenase (amino acid catabolism). Because these enzymes are essential for ATP production, tissues with high metabolic demand—neurons and cardiac myocytes—are most vulnerable to deficiency.

Causes of deficiency include chronic alcoholism (impaired absorption, storage, and utilization), malnutrition, bariatric surgery, prolonged parenteral nutrition without supplementation, and hyperemesis gravidarum.

Clinical syndromes: - Wernicke encephalopathy: classic triad of confusion, ophthalmoplegia (often CN VI palsy, nystagmus), and ataxia due to damage to mammillary bodies, thalamus, and periaqueductal gray matter. - Korsakoff syndrome: irreversible memory impairment (anterograde and retrograde amnesia) with confabulation, resulting from chronic Wernicke damage to mammillary bodies and dorsomedial thalamic nuclei. - Dry beriberi: symmetric peripheral neuropathy (sensory > motor), muscle wasting. - Wet beriberi: high-output cardiac failure due to peripheral vasodilation and impaired myocardial energy metabolism, presenting with edema, dilated cardiomyopathy.

A critical clinical pearl for boards: always administer thiamine BEFORE glucose in suspected thiamine deficiency (e.g., alcoholic or malnourished patients) to prevent precipitating or worsening Wernicke encephalopathy, since glucose metabolism rapidly depletes remaining thiamine stores.

Diagnosis can be supported by the RBC transketolase activity assay (increased activity after thiamine administration indicates deficiency) though clinically diagnosis is often presumptive. Treatment is IV thiamine repletion.

High-yield associations: Beriberi, Wernicke-Korsakoff, alcoholics, malnutrition, TPP-dependent enzymes (mnemonic: 'TPP is a Big Toy Kit' - Transketolase, Pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, Branched-chain ketoacid dehydrogenase).