In DSM-II, this category is called Senile and Pre-senile dementia
This syndrome occurs with senile brain disease, whose causes are largely unknown. The category does not include the pre-senile psychoses nor other degenerative diseases of the central nervous system. While senile brain disease derives its name from the age group in which it is most commonly seen, its diagnosis should be based on the brain disorder present and not on the patient's age at times of onset. Even mild cases will manifest some evidence or organic brain syndrome: self-centeredness, difficulty in assimilating new experiences, and childish emotionality. Deterioration may be minimal or progress to vegetative existence.
This category includes a group of cortical brain diseases presenting clinical pictures similar to those of senile dementia but appearing characteristically in younger age groups. Alzheimer's and Pick's diseases are the two best known forms, each of which has a specific brain pathology.
When the impairment is not of psychotic proportion the patient should be classified under Non-psychotic Organic Brain Syndrome with Senile or Pre-senile brain disease