Basic Neurosciences · Paper A
Thiamine deficiency syndromes
Thiamine (vitamin B1) deficiency causes a spectrum of brain syndromes, most often in alcohol dependence, and the order of treatment matters as much as the diagnosis itself. Take a malnourished patient given IV glucose before thiamine in A&E: that routine-seeming order can precipitate florid Wernicke's encephalopathyAn acute brain condition from thiamine deficiency causing confusion, ataxia, and abnormal eye movements.Read more → in someone who was only borderline deficient before, e.g. one unthinking sequence of drugs turning a subclinical deficiency into an acute emergency. Identify nutritional risk early and give parenteral thiamine promptly whenever Wernicke's encephalopathy is suspected.
Wernicke's encephalopathyAn acute brain condition from thiamine deficiency causing confusion, ataxia, and abnormal eye movements.Read more → is the acute, treatable phase: confusion, ophthalmoplegiaWeakness or paralysis of the muscles that move the eyes.Read more → (weakness of the eye-movement muscles, causing abnormal eye movements) and ataxiaLoss of full control of body movements, causing an unsteady, uncoordinated gait or actions.Read more → (unsteady, uncoordinated movement) together, though all three occurring at once is uncommon, so treat on suspicion alone. Korsakoff's syndrome is the chronic phase: severe anterograde amnesia with confabulationFilling a gap in memory with a made-up answer the person genuinely believes is true, not a deliberate lie.Read more → (filling memory gaps with invented, not deliberately false, details), alongside relative preservation of other thinking. An at-risk patient with confusion and gait ataxia but no eye signs still needs treatment for suspected Wernicke's encephalopathy: the incomplete triad is common, not the exception. Parenteral thiamine is given before any glucose whenever deficiency is suspected, since the order of treatment can be the difference between reversible and permanent damage.
A fresh doctor might treat thiamine deficiency as a routine vitamin top-up, something to add alongside other fluids. That reflex is dangerous here: giving glucose before thiamine to a deficient patient can trigger the very brain injury the vitamin was meant to prevent. Hold the phrase THIAMINE BEFORE GLUCOSE through every section below: it is the single fact this whole topic exists to teach.
Thiamine (vitamin B1) is a cofactor (a helper molecule) needed for several enzymes in glucose metabolism, particularly in energy-hungry brain tissue. Deficiency most often arises from chronic alcohol use (through poor dietary intake, reduced gut absorption, and reduced liver storage) but can also occur with malnutrition, hyperemesis (severe, prolonged vomiting) in pregnancy, bariatric surgery, or prolonged intravenous feeding without vitamin supplementation. Deficiency produces a spectrum: an acute, treatable phase called , and, if untreated, a chronic phase called Korsakoff's syndrome.
A common mistake is assuming only happens in patients with obvious alcohol dependence. Any severely malnourished patient (including someone with hyperemesis in pregnancy, prolonged fasting, or malabsorption after bariatric surgery) carries the same risk, and thiamine should be given before glucose in any such patient regardless of whether alcohol is part of the history at all. A second common mistake is waiting for the complete triad of confusion, , and before treating; since the full triad is uncommon, treatment on suspicion alone is the correct and expected approach.
Imagine a malnourished patient arriving in the emergency department who is given a bag of intravenous glucose before anyone thinks about thiamine. Glucose metabolism itself consumes thiamine as a cofactor, so loading a thiamine-deplete patient with glucose can rapidly exhaust what little thiamine remains and precipitate florid in someone who was only borderline deficient beforehand. This is why the working principle is not just "give thiamine" but specifically "give thiamine BEFORE glucose" in anyone at nutritional risk.
is classically described by a triad: confusion, (weakness of the eye-movement muscles, producing abnormal eye movements such as or a squint), and (unsteady, uncoordinated movement, especially of gait). The full triad, however, is present in only a minority of confirmed cases, so clinicians are taught to treat on clinical suspicion rather than wait for all three features together. Wernicke's encephalopathy is a medical emergency and is reversible with prompt parenteral (given by injection or infusion, not by mouth) thiamine.
Left untreated, can progress to Korsakoff's syndrome, a chronic amnestic state. Its hallmark is severe anterograde amnesia (inability to form new memories from the point of the injury onward), often with (unconsciously filling memory gaps with invented, not deliberately false, details) and, distinctively, relatively preserved immediate recall and preserved general intelligence and social skills otherwise. Structurally, the mammillary bodies and the dorsomedial (mediodorsal) nucleus of the are the brain regions most consistently affected, which correlates with the memory-specific pattern of the deficit.
should not be confused with simple alcohol intoxication or alcohol withdrawal: intoxication and withdrawal have their own distinct time courses and features (such as tremor, autonomic hyperactivity, and seizures in withdrawal), whereas Wernicke's specifically brings the confusion-- pattern and requires urgent thiamine rather than sedation alone. Korsakoff's syndrome should not be confused with delirium: Korsakoff's is a relatively stable, chronic amnestic state with preserved alertness, whereas delirium involves a fluctuating level of consciousness and attention. Hepatic , another cause of confusion in patients with alcohol-related liver disease, presents with asterixis (a flapping tremor) and a raised ammonia level rather than the ophthalmoplegia and ataxia of Wernicke's.
is a clinical diagnosis, not a laboratory one: by the time a confirmatory blood thiamine level came back, treatment delay could cause irreversible harm, so the diagnosis rests on recognising the pattern and treating on suspicion. A widely used clinical rule, the Caine criteria, holds that a patient meeting at least two of four features (dietary deficiency, oculomotor abnormalities, cerebellar signs, and either an altered mental state or mild memory impairment) should be treated as Wernicke's encephalopathy, precisely because waiting for the classic full triad misses too many real cases. MRI brain can support the diagnosis by showing characteristic changes around the mammillary bodies and periaqueductal , but a normal scan never rules Wernicke's out, so imaging supports, and never overrides, clinical suspicion.
Management follows the core principle taught throughout UK practice and reflected in NICE and Maudsley Prescribing Guidelines-aligned care: give parenteral thiamine promptly whenever is suspected, and do so BEFORE giving any glucose-containing fluid, since the reverse order risks precipitating the very syndrome being prevented. Prompt parenteral thiamine can substantially reverse the acute features of Wernicke's encephalopathy, but once Korsakoff's amnesia is established it often persists despite treatment, which is why the acute window is treated as a genuine emergency rather than something to address routinely on a ward round.
Vignettes often describe a malnourished or alcohol-dependent patient who becomes acutely more confused shortly after being given intravenous dextrose (glucose) in the emergency department: the expected answer recognises this as a precipitant of from glucose given before thiamine, not a coincidental deterioration. A further trap places the presentation in a non-alcohol context, such as hyperemesis in pregnancy, to test whether candidates wrongly assume Wernicke's requires an alcohol history.
Thiamine deficiency runs from acute, reversible (confusion, , : treated on clinical suspicion, using the Caine criteria, not the full triad) to chronic, often irreversible Korsakoff's amnesia, and the one rule that governs every step of management is thiamine before glucose, always.