Wernicke + Korsakoff: Thiamine, Before Glucose, Always
B1 Deficiency · The Brain Energy Crash
Wernicke + Korsakoff: Thiamine, Before Glucose, Always
Thiamine runs four enzymes the brain cannot live without. Take it away, and the mammillary bodies are the first to fall. Give glucose without thiamine in a chronic drinker, and you just precipitated Wernicke.
Rule One · Banana Bag Before Dextrose
Case 0 · ED at 2 AM
A 56-year-old man with chronic alcohol use is brought to the ED for confusion. On exam he has horizontal nystagmus, an ataxic gait, and is oriented only to person. Glucose is 58. The resident hangs IV dextrose and within minutes the patient becomes more obtunded and develops gaze paralysis.
What did the resident miss?
The triad was already on the table: confusion + nystagmus + ataxia = Wernicke encephalopathy. He needed IV thiamine first. Pushing dextrose into a thiamine-depleted brain forces the remaining B1 into glycolysis (transketolase, PDH) and burns through it in minutes. The brain runs out of cofactor, energy collapses, and the patient crashes into florid Wernicke or straight into coma.
In any malnourished or alcohol-using patient: thiamine before glucose. Not "with." Before.
Acute Phase · Reversible
The Wernicke Triad
Three findings, one window. Catch all three together and you have hours, not days, to land thiamine before the damage hardens into Korsakoff. Tap each card.
Sign 01
Confusion
Global encephalopathy. Disoriented, drowsy, often misread as "just intoxicated."
What it looks like: apathetic, slow to respond, can sometimes follow simple commands but forgets the room. Easy to write off as drunk in the ED, which is exactly why Wernicke gets missed at triage. Pearl: any altered chronic drinker gets empiric IV thiamine before glucose, no labs required.
Tap to expand ↓
Sign 02
Nystagmus / Ophthalmoplegia
Horizontal nystagmus first, then lateral rectus palsy (CN VI), then conjugate gaze paralysis.
The brainstem oculomotor nuclei (CN III, CN VI) sit right next to the periaqueductal gray, one of the first zones to enhance on MRI. The eyes are the early-warning siren: horizontal nystagmus shows up before anything else and reverses fast with thiamine, often within hours. If you see bilateral lateral rectus palsy in a malnourished patient, that is Wernicke until proven otherwise.
Tap to expand ↓
Sign 03
Ataxia
Wide-based, staggering gait. Truncal more than appendicular. From cerebellar vermis injury.
Thiamine deficiency hits the superior cerebellar vermis hardest, which controls trunk and gait coordination. So the patient looks fine sitting still and falls apart the moment they stand. Heel-to-shin can be normal even when they cannot walk a straight line. Caveat: alcoholic cerebellar degeneration looks identical, often coexists, and is the part that may not fully reverse even with thiamine.
Tap to expand ↓
High-yield: only about 10 percent of Wernicke patients show the full classic triad. Most show one or two. If you wait for all three, you missed it.
Chronic Phase · Irreversible
What Untreated Wernicke Becomes
When the acute window closes without thiamine, the mammillary bodies atrophy and the memory machinery fails for good. Korsakoff is the scar.
C
Confabulation
The patient fills memory gaps with plausible but fabricated stories, told without insight or deceit. Not lying. They genuinely believe the made-up version. Path classic: ask what they did yesterday, hear a coherent story that never happened.
A
Anterograde Amnesia
Cannot form new memories. Greet them, leave the room for ten minutes, come back, and they will not recognize you. The mammillary bodies and medial thalamus feed the Papez circuit; lose them and consolidation stops.
P
Personality Change
Apathy, blunted affect, loss of initiative. Less commonly disinhibition. Family describes them as "still here but not the same." Lack of insight into their own memory deficit is part of the syndrome.
MRI signature: mammillary body atrophy is the chronic hallmark. On acute Wernicke, look for symmetric T2/FLAIR enhancement of the mammillary bodies, medial thalami, and periaqueductal gray.
A patient is confused, staggering, and has horizontal nystagmus. What do you commit to before any dextrose?
This is the acute window: confusion plus eye findings plus ataxia. The bedside decision is IV thiamine now, because imaging can wait and glucose can worsen the crash if B1 is depleted.
A patient is alert but cannot form new memories and fills gaps with confident false stories. Which phase are you seeing?
That is the scar phase: mammillary body injury has broken memory consolidation. Thiamine still prevents more damage, but established Korsakoff memory loss is often permanent.
Mechanism · Why the Brain Crashes
Four Enzymes, One Cofactor
Thiamine pyrophosphate (TPP) is a cofactor for four enzymes that together run carbohydrate energy, amino acid breakdown, and the NADPH pool. Pull out TPP and all four stall at the same time. The brain, which runs almost entirely on glucose, fails first.
TPPThiamine PP
The cofactor that feeds four enzymes
Enzyme 01
Pyruvate Dehydrogenase
Glycolysis → TCA cycle
Converts pyruvate into acetyl-CoA. Without it: pyruvate piles up and shunts to lactate. Glucose cannot enter the TCA cycle, ATP production collapses. Brain neurons that depend entirely on glucose are the first casualty.
Enzyme 02
Alpha-Ketoglutarate Dehydrogenase
TCA cycle rate-limiting step
Converts alpha-ketoglutarate into succinyl-CoA inside the TCA cycle. Without it: the TCA cycle grinds to a halt at the rate-limiting step. NADH and ATP output crash even if PDH still had any fuel to send through.
Enzyme 03
Branched-Chain AA Dehydrogenase
Leucine, Isoleucine, Valine breakdown
Breaks down the branched-chain amino acids leucine, isoleucine, and valine. Without it (genetic version): maple syrup urine disease, sweet-smelling urine, neonatal encephalopathy. In adult B1 deficiency the contribution to the energy crash is real but smaller than PDH or alpha-KG DH.
Enzyme 04
Transketolase
Pentose phosphate pathway
Shuffles sugars through the non-oxidative arm of the pentose phosphate pathway. Without it: ribose-5-phosphate for nucleotides drops, and the recycled NADPH (used downstream for glutathione regeneration) gets squeezed. Clinical labs measure RBC transketolase activity as the classic confirmatory test for B1 deficiency.
All four enzymes stall at the same instant. PDH→ glucose cannot enter the TCA cycle. Alpha-KG DH→ TCA cycle blocked at its rate-limiting step. BCAA DH→ amino acid fuel pathway closed. Transketolase→ pentose phosphate and NADPH supply pinched. The brain, which has no fat-burning fallback, runs out of ATP within hours. Neurons in the periventricular gray, mammillary bodies, and medial thalamus die first because they have the highest baseline metabolic demand and the worst capillary safety margin.
Management · The Rule
Thiamine First. Always.
The single most testable point on this entire page lives in this section. Glucose without thiamine in a chronic drinker is not neutral; it actively burns the patient's last reserves.
!
Banana Bag Before Dextrose
In any chronic drinker, malnourished patient, or anyone with possible thiamine depletion (bariatric surgery, hyperemesis, prolonged TPN): give IV thiamine before any glucose-containing fluid. Glucose without thiamine consumes residual B1 through transketolase and PDH and can precipitate acute Wernicke.
01
IV Thiamine, immediately
500 mg IV three times daily for 2 to 3 days for active Wernicke. High dose, parenteral, no oral substitute in the acute phase. Oral B1 has poor absorption, especially in alcohol-use patients.
02
Magnesium replacement
Mg is a cofactor for thiamine pyrophosphate function. Chronic drinkers are almost always hypomagnesemic; correct it or the thiamine you just gave is half useless.
03
Now the dextrose
After thiamine is on board, glucose is safe and often needed (these patients are usually hypoglycemic). Keep B1 running through the admission.
04
Transition to oral, then maintenance
Oral thiamine 100 mg daily long-term if the underlying deficiency persists. Pair with a multivitamin (folate, B12, the rest of the B complex) and treat the upstream cause: alcohol use disorder, malabsorption, hyperemesis, refeeding plan.
!
Never reverse this order
Glucose first in a deficient patient = iatrogenic Wernicke. This is the single most testable medical-error vignette on the board for this topic.
Anatomy · The Sites That Fall
Where the Damage Lives
Coronal slice at the level of the mammillary bodies. Toggle between a healthy brain, acute Wernicke (enhancement of the mammillary bodies, medial thalami, and periaqueductal gray), and chronic Korsakoff (mammillary atrophy).
Healthy. Mammillary bodies and medial thalami at baseline. The Papez circuit relays freely.
Coronal anatomy reference for the mammillary body region.Imaging reference slot for symmetric medial thalamic and mammillary body involvement.Memory circuit reference for mammillary body and thalamic relay anatomy.
Side by Side · The Spectrum
Wernicke vs Korsakoff
Same disease, two phases. Acute and reversible up top; chronic and locked-in below. The line between them is whether thiamine arrived in time.
Onset: the chronic residue of untreated or repeated Wernicke episodes.
MRI: mammillary body atrophy is the classic chronic finding. Often coexisting cortical and cerebellar atrophy.
Treatment: ongoing thiamine and abstinence, but the cognitive deficit usually does not reverse. Manage safety, supervise medications, treat alcohol use disorder.
Prognosis: permanent. Confabulation may soften over months but anterograde amnesia tends to stay.
Quiz · Six Vignettes
clinical Self-Check
Six original vignettes covering the triad, the iatrogenic-Wernicke trap, the four enzymes, mammillary anatomy, Korsakoff confabulation, and the Wernicke-to-Korsakoff progression. Take your time.
confusionhorizontal nystagmuswide-based gaitlow serum glucoseRoux-en-Y gastric bypassvomiting after mealsmedial thalamic enhancementmammillary body enhancementconfabulationanterograde amnesiamammillary body atrophyPapez circuithyperemesis gravidarumketonuriatruncal ataxiathiamine depletionpyruvate dehydrogenasealpha-ketoglutarate dehydrogenasebranched-chain amino acid dehydrogenasetransketolasepernicious anemialow B12hypomagnesemiacirrhosisnormal early MRIperiaqueductal graydorsomedial thalamuslateral gaze palsyTPP activation assaypentose phosphate pathwayribose-5-phosphateNADPH supplythiamine before dextroseIV thiaminedextrose first trapmemory consolidation
clinical Walkthrough
clinical Walkthrough
Original clinical vignettes. Shuffled, never-repeat, full explanations for every choice.
Medically reviewed by Kaitlyn Cocuzzo, MD and Fatima Ali, DO · Last updated June 30, 2026 at 10:52 AM ET
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