My Husband Was Diagnosed With Chirosis Of The Liver Due

My husband was diagnosed with chirosis of the liver due to alcohol consumption. He is tryig to get disability due to the fact he cannot perform his duties at work because of the lack of cognitive brain function. Aetna wants clinical information supporting this, and a letter from his gastroenterologist is not good enough. Who should he see to perform the necessary testing? I believe it is called Korsakoffs psychosis.