Wernicke's encephalopathy is a disease state arising from thiamine deficiency, where the failure of thiamine to act as a co-factor in gucose metabolism results in neuronal damage. Characteristic features are delirium, gait disturbance, nystagmus and some sort of oculomotor prblem like a gaze palsy. This condition has appeared in the SAQs several times:
Usually, the candidates were given both a characteristic history and a biochemical picture of hyponatremia hypoglycaemia and high cholesterol.
The administration of glucose to a patient who has a thiamine deficiency tends to precipitate an acute Wernicke's encephalopathy. Watson et al (1981) presented a case series of non-alcoholic malnourished patients all of whom developed the encephalopathy after having a bolus of dextrose.
There is some concern about giving glucose to the hypoglycaemic patient at risk of Wernicke's. This is patently absurd, as the complications of neuroglycopenia will be much more damaging in the long run than the manifestations of Wernicke's , given that the former are reversible and mild, whereas the latter are irreversible and severe (Gussow et al, 2007).
Clinical signs of thiamine deficiency develop when cerebral thiamine levels drop to 20% below baseline (Isenberg-Grzeda et al, 2012). It can be rapid in onset: four days of low thiamine is enough.
Royal College Criteria
European Federation of Neurologic Societies
Wernicke's encephalopathy is a clinical diagnosis. However, thiamine deficiency is readily diagnosed by the levels of red cell transketolase. One may test the levels before and after thiamine supplementation. A low transketolase level along with a >25% rise in level following thiamine supplementation is diagnostic of thiamine deficiency.
The treatment consists of some IV thiamine. The college answer to Question 13.3 from the second paper of 2013 suggests 100mg IV daily is a big enough dose. However, there is disagreement as to how much is enough. A Cochrane review (Day et al, 2013) was not able to reach any sensible conclusions about the dosage, siting methodological problems in the one and only trial which met the inclusion criteria (Ambrose et al, 2001). This trial found a relationship between dose and response (more was better: 200mg vs 100mg daily). It may be reasonable to give large amounts; Cook et al (1998) recommended 1g daily. Locally, 300mg IV three times a day is given. UpToDate recommends the largest dose, 500mg three times a day. The rationale for such massive doses is the theoretical benefit of producing a steep blood-to-brain thiamine concentration gradient, to facilitate its passive diffusion into the neurons.