This is a reversible dementia brought about by poor diet and in particular a severe deficiency of Thiamine (Vitamin B1), and nowadays is almost exclusiveley caused by excessive alcohol consumption

Thiamine deficiency leads to the disease Beriberi of which there are two types, both of which are often alcohol related. Alcohol reduces the bodies ability to process Thiamine resulting in 'wet' or 'dry' Beriberi

Symptoms of wet beriberi include swelling, increased heart rate, lung congestion and may lead to an enlarged heart and congestive heart failure

Dry beriberi includes pain, tingling and burning sensations, numbness and loss of sensations in the extremities. Muscle wasting and associated loss of physical functions ensue, which without treatment can lead to paralysis of the lower extremities, brain damage and death

Diagnosis includes tests for blood & urinary Thiamine levels and physical examination. Confirmation is by administering Thiamine to see if the patient improves

Treatment for Wernicke's encephalopathy includes Thiamine replacement. The symptoms may subside, but may be replaced by Korsakoff's syndrome, which includes retrograde amnesia (memory loss), impaired ability to learn, and confabulation (making up stories to explain behavior that have little relation to reality)

There is a good chance of full recovery if treated early enough, although more advanced cases may leave a person with memory loss or other mental imparement. Continued alcohol abuse may make treatment worthless see:  http://compuserve.thirdage.com/health/adam/ency/article/000771.htm