Depressed patients are not disoriented. In pure and full form, depression can usually be distinguished based on standard diagnostic criteria. Many of the symptoms are overlapping or shared in common. Variety of combinations and overlaps are quite frequent. Some patients have depression accompanied by some cognitive dysfunction.
Some patients have dementia with an accompanying mood disturbance.
Of course, some patients have dementia and depression. These are both common disorders. Distinguishing those three can be very difficult. The idea, the concept of depressive pseudodementia, that is that some elderly patient s who looked demented really have depression and that treating the depression will entirely cure their cognitive difficulties has not been supported by intervention studies. Trials of antidepressants in patients who have symptoms of both depression and dementia generally show improvement in mood and energy but no improvement in cognition.