This was a term developed by a professor by the name of Arnold Pick in 1891. As its notably Latin roots suggest, this is a psychiatric disorder which is characterised by a premature and rapidly diminishing cognitive ability. One of the defining metrics is therefore an onset of the disease in the latter half of the teenage years or into early adulthood. It should be noted here that the pathology of this condition would later be classified as the familiar term schizophrenia. While the causes of this dementia were not well understood at the time, it was assumed that the condition was incurable and cognitive deterioration was all but inevitable.
It is important to realise that (according to Dr. Pick) the primary characteristic of dementia praecox is a cognitive deterioration as opposed to an emotional or mood-related impact (although the flattening or distorting of emotions can sometimes be observed). The signs of this illness can begin in one's early teen years. Therefore, age is the first important variable that needs to be considered. As with many other mental disorders, this dementia can begin rather subtly and progress into more noticeable symptoms as the years progress. During this time period, the patient may also display emotional changes such as the aforementioned "flattening" of emotional expression, speech tonality and the reaction to profound life events. In and of itself, this could be mistaken for other conditions such as schizoaffective disorder. This likely led to many misdiagnoses in the past. The key is therefore an examination of the cognitive process.
Much like in someone suffering from age-related dementia, the symptoms of dementia praecox are quite similar. These will include (but may not be limited to):
While primarily cognitive in its presence, we must recall that the portions of the brain which are affected are also associated with emotional responses. Therefore, other symptoms of dementia praecox can include restlessness, a prolonged state of anxiety, anger and the proclivity to become extremely defensive. Occasionally, these can exist alongside delusions and hallucinations. He or she may feel paranoid and as if they are being plotted against. Hallucinations can be auditory, visual and sensory. In the most severe cases, the patient may very well begin to lose touch with reality altogether.
So, it is clear to see that while this term may indeed be outdated, the symptoms involved are still those commonly seen with schizophrenic patients. The key is to take into account the cognitive aspects of the behavior and to correlate this with both the age of the patient as well as his or her emotional state. As research progresses, it is hoped that more effective treatment methods are discovered.