Depressed elderly patients often show signs of cerebrovascular disease, commonly known as a stroke. Some scientists theorize that having cerebrovascular disease may affect depression in older adults in one of three ways: by causing depression, by making it more likely that people who have been depressed have a relapse, or by maintaining certain depressive symptoms in those already depressed. The combination of depression and cerebrovascular disease in older adults is referred to as vascular depression and is associated with psychomotor slowing, functional impairment, and cognitive impairment. Additionally, the likelihood of improvement or remission is lower in vascular depression and is more difficult to treat over time.