Same molecule. Two organs. Three diseases. Here's the whole map from mechanism to clinical medicine move.
The Mechanism
Vitamin B1→Thiamine Pyrophosphate (TPP)→4 enzymes
B1 must be converted to TPP before it can do anything. TPP is the active coenzyme form.
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Pyruvate Dehydrogenase
PDH
▼
Converts pyruvate → acetyl-CoA. Entry point to the Krebs cycle. Without it, the cell can't generate ATP aerobically.
❤️ Heart-critical
⚡
Alpha-KG Dehydrogenase
Krebs cycle step 4
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Converts alpha-ketoglutarate → succinyl-CoA inside the Krebs cycle. Loss stalls the cycle mid-way. ATP production collapses.
❤️ Heart-critical
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Branched-Chain AA DH
BCAA catabolism
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Breaks down branched-chain amino acids (Leu, Ile, Val). Deficiency here also causes Maple Syrup Urine Disease when the enzyme is congenitally absent.
❤️ Heart-critical
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Transketolase
Pentose phosphate pathway
▼
Runs the pentose phosphate pathway in the brain. Generates NADPH (antioxidant defense) and ribose-5-phosphate (nucleotide synthesis). Brain neurons are uniquely dependent on this.
🧠 Brain-critical
The split that explains everything: The heart depends on all 3 dehydrogenases to run Krebs and make ATP. The brain depends on transketolase for neuronal metabolism. Same B1 deficiency → different organ failures. That's why beriberi (heart) and Wernicke's (brain) are separate diseases with the same root cause.
The Full B1 Deficiency Spectrum
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Dry Beriberi
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Wet Beriberi
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Wernicke's Enceph.
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Wernicke- Korsakoff
Dry Beriberi
Heart is dilating but compensating. No fluid yet. The name is literal: no edema, no wet lungs.
Peripheral neuropathy (hands and feet)
Symmetric muscle wasting
Weakness, loss of deep tendon reflexes
Cardiac dilation starting → not yet in failure
Wet Beriberi
The heart has given out. Massive ventricular dilation. Fluid floods the lungs and peripheral tissues.
Pulmonary edema (wet lungs → hence the name)
Pitting edema bilaterally
High-output cardiac failure (vasodilation forces the heart to work harder)
S3 gallop, cardiomegaly on CXR
Why high-output? Peripheral vasodilation drops systemic resistance. To maintain perfusion, the heart compensates by increasing output. Eventually it can't keep up and fails → but cardiac output is still elevated at time of presentation.
Wernicke's Encephalopathy
The brain target. Affects mammillary bodies, periaqueductal gray, and dorsomedial thalamus · NOT the posterior temporal lobe (that's Wernicke's Area/Aphasia, a completely different entity). ATP depletion from PDH and alpha-KG dehydrogenase failure → thiamine-sensitive regions die.
Classic triad: confusion, ophthalmoplegia, ataxia
Board trap: Wernicke's ENCEPHALOPATHY (thiamine deficiency) vs Wernicke's AREA (temporal lobe, language) · two different things, one name
Mammillary body damage visible on MRI
This is the emergency. If you give glucose before thiamine, you burn the last remaining B1 and tip Wernicke's into the irreversible Korsakoff stage.
Wernicke-Korsakoff Syndrome
Mammillary bodies now also involved. This is the irreversible stage.
Confabulation → patient makes up stories to fill memory gaps (not lying, not aware they're doing it)
Unable to move short-term memory into long-term memory
Mammillary body atrophy on MRI
Anterograde amnesia (can't form new memories)
clinical medicine distinction: Wernicke's is reversible with thiamine. Once Korsakoff sets in, the amnesia is permanent even after thiamine replacement.
Why The Names
DRY
No fluid accumulation
The body is failing but hasn't flooded yet. Nerves are dying, muscles are wasting, the heart is dilating → but the vasculature hasn't failed enough to leak fluid. No edema. No wet lungs.
WET
Fluid in lungs and tissues
The heart has given out. Backward failure backs fluid into the lungs and peripheral tissues. Pulmonary edema. Pitting edema. Literally wet. The dam broke.
Side by Side
🔶 Dry Beriberi
🔷 Wet Beriberi
Heart
Dilating, compensating
Massive dilation, failing
Fluid
None → no edema
Pulmonary edema + pitting edema
Neuro
Peripheral neuropathy, wasting
Same, plus cardiac symptoms
Output
Normal or low
High-output failure
Urgency
Serious
More urgent → end-stage
Cause
Both: Thiamine (B1) deficiency
Treatment
IV Thiamine → before any glucose
Diagnose the Case
Case Challenge
Four patients. One diagnosis each.
0/4
Finished. Good run.
Board Attack Protocol
3-Step Strategy → p.24
1
Name it. What does the patient have? Identify the diagnosis before anything else. Stem clues: alcoholic or malnourished, cardiac dilation, neuropathy.
2
Pathophysiology. Why is this happening? No B1 → no TPP → heart can't run Krebs → no ATP → dilation → failure. Naming the mechanism unlocks the next step.
3
What kills first. Rule out the most dangerous thing. In beriberi: wet kills faster than dry. But in the context of Wernicke's → giving glucose without thiamine is the move that tips reversible into irreversible.
The critical board move: Thiamine IV before glucose. Always. Giving dextrose first burns the last thiamine reserves and precipitates Wernicke's encephalopathy → or tips existing Wernicke's into permanent Korsakoff amnesia.
Symptom Sorter
Sort the Symptoms
Tap a symptom to select it, then tap the correct bucket.
🔶 Dry Beriberi
🔷 Wet Beriberi
Quick Quiz
Q 1
Why does wet beriberi cause high-output heart failure rather than the classic low-output pattern seen in ischemic cardiomyopathy?
B. In wet beriberi, metabolic dysfunction causes systemic peripheral vasodilation. Reduced vascular resistance means the heart has to pump more to maintain adequate tissue perfusion. The heart works harder and harder until it finally fails → but cardiac output is still high at the time you see the patient. This pattern (high output, dilated ventricles) also appears in severe anemia, hyperthyroidism, Paget disease, and AVM syndromes.
Q 2
An alcoholic man is brought to the ER. He is confused, ataxic, and has paralysis of his lateral gaze. You give him IV dextrose. Two days later he no longer confabulates stories about his fishing trips and can no longer form new memories. What happened?
C. Classic clinical medicine trap. The confusion, ataxia, and ophthalmoplegia were Wernicke's → still reversible at that point. Giving dextrose without thiamine forced glucose oxidation, consuming the last available thiamine. Once mammillary bodies are damaged (Korsakoff stage), the confabulation and inability to form new memories are permanent. The lesson: in any alcoholic or malnourished patient → give thiamine first, glucose second, every time.
Q 3
Which of the following best explains why the heart fails in beriberi while the kidneys and liver are relatively spared?
A. The heart is uniquely vulnerable because it depends on all three TPP-dependent dehydrogenases (pyruvate DH, alpha-KG DH, branched-chain AA DH) to sustain aerobic ATP production. It can't compensate aerobically without all three running. The brain targets transketolase specifically → a different enzyme → which is why the same deficiency hits the brain and heart with different clinical pictures. Other organs have more metabolic flexibility or lower ATP demand relative to their mass.
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