Wernicke encephalopathy results from inadequate intake or absorption of thiamin plus continued carbohydrate ingestion. Severe alcoholism is a common underlying condition. Excessive alcohol intake interferes with thiamin absorption from the gastrointestinal tract and hepatic storage of thiamin; the poor nutrition associated with alcoholism often precludes adequate thiamin intake.
Wernicke encephalopathy may also result from other conditions that cause prolonged undernutrition or vitamin deficiency (eg, recurrent dialysis, hyperemesis, starvation, gastric plication, cancer, AIDS). Giving a carbohydrate load to patients with thiamin deficiency (ie, refeeding after starvation or giving IV dextrose-containing solutions to high-risk patients) can trigger Wernicke encephalopathy.
Not all thiamin-deficient alcohol abusers develop Wernicke encephalopathy, suggesting that other factors may be involved. Genetic abnormalities that result in a defective form of transketolase, an enzyme that processes thiamin, may be involved.
Characteristically, central nervous system lesions are symmetrically distributed around the 3rd ventricle, aqueduct, and 4th ventricle. Changes in the mamillary bodies, dorsomedial thalamus, locus ceruleus, periaqueductal gray matter, ocular motor nuclei, and vestibular nuclei are common.
In patients with Wernicke encephalopathy, clinical changes occur suddenly.
Oculomotor abnormalities, including horizontal and vertical nystagmus and partial ophthalmoplegias (eg, lateral rectus palsy, conjugate gaze palsies), are common. Pupils may be abnormal; they are usually sluggish or unequal.
Vestibular dysfunction without hearing loss is common, and the oculovestibular reflex may be impaired. Gait ataxia may result from vestibular disturbances, cerebellar dysfunction, and/or polyneuropathy; gait is wide-based and slow, with short-spaced steps.
Global confusion is often present; it is characterized by profound disorientation, indifference, inattention, drowsiness, or stupor. Peripheral nerve pain thresholds are often elevated, and many patients develop severe autonomic dysfunction characterized by sympathetic hyperactivity (eg, tremor, agitation) or hypoactivity (eg, hypothermia, postural hypotension, syncope). In untreated patients, stupor may progress to coma, then to death.
There are no specific diagnostic studies. Diagnosis of Wernicke encephalopathy is clinical and depends on recognition of underlying undernutrition or vitamin deficiency. There are no characteristic abnormalities in cerebrospinal fluid, evoked potentials, brain imaging, or electroencephalogram. However, these tests, as well as laboratory tests (eg, blood tests, glucose, complete blood count, liver tests, arterial blood gas measurements, toxicology screening), should typically be done to rule out other etiologies. Thiamin levels are not routinely measured, because serum thiamin levels do not always reflect cerebrospinal fluid levels and normal serum levels do not exclude the diagnosis.
Prognosis depends on timely diagnosis of Wernicke encephalopathy. If begun in time, treatment may correct all abnormalities. Ocular symptoms usually begin to abate within 24 hours after early thiamin administration. Ataxia and confusion may persist days to months. Memory and learning impairment may not resolve completely. Untreated, the disorder progresses; mortality is 10 to 20%. Of surviving patients, 80% develop Korsakoff psychosis; the combination is called Wernicke–Korsakoff syndrome.
Treatment of Wernicke encephalopathy consists of immediate administration of thiamin 100 mg IV or IM, continued daily for at least 3 to 5 days. Magnesium is a necessary cofactor in thiamin-dependent metabolism, and hypomagnesemia should be corrected using magnesium sulfate 1 to 2 g IM or IV every 6 to 8 hours or magnesium oxide 400 to 800 mg orally once/day. Supportive treatment includes rehydration, correction of electrolyte abnormalities, and general nutritional therapy, including multivitamins. Patients with advanced disease require hospitalization. Alcohol cessation is mandatory.
Because Wernicke encephalopathy is preventable, all undernourished patients should be treated with parenteral thiamin (typically 100 mg IM followed by 50 mg orally once/day) plus vitamin B12 and folate (1 mg orally once/day for both), particularly if IV dextrose is necessary. Thiamin is also prudent before any treatment is begun in patients who present with a reduced level of consciousness. Patients who are undernourished should continue to receive thiamin as outpatients.