Differential diagnosis of dementia
Aging and cognitive decline
There is a natural age-associated modification in cognition. As a consequence, it can be problematic distinguishing between cognitive impairment associated with normal aging and early dementia. In addition, ‘mild cognitive impairment’ (MCI) can be experienced. This is characterized by an abnormal level of cognitive impairment, albeit that it does not fulfill dementia criteria as it is insufficient to cause functional decline. It should be noted that MCI is not a feature of normal aging. Some individuals develop MCI but do not develop dementia. However, many patients with MCI do go on to develop dementia.
It is important to distinguish the early stages of dementia from the cognitive changes that can occur with normal aging. During normal aging, the ability to learn and acquire information declines gradually. The ability to recall information remains relatively preserved. This is very different from the early stages of dementia, in particular AD. In AD, there is a progressive decline in learning and the ability to recall information.
Dementia, delirium, depression and drugs
If a patient presents with memory loss, the differential diagnosis should include the ‘4 Ds’; delirium, depression, drugs, and dementia.
The cognitive impairment that often accompanies delirium and depression can be mistaken for, or can coexist with, dementia. Evidence of delirium or depression should be addressed promptly. Although delirium is common in older adults with acute illnesses, it often goes unrecognized in the clinical setting. Likewise, although depression occurs frequently in older adults, it is under-diagnosed. Some of the factors to distinguish dementia from delirium are detailed in Table 2 below.
Table 2. Distinguishing between degenerative dementia and delirium (Ham 1997, reproduced by kind permission of Mosby-Year Book, Inc.)
It is essential that delirium is discounted as early as possible. The underlying physical disorder, together with decline in cognition, may constitute a medical emergency. Immediate evaluation of the underlying causes and initiation of possible treatment is imperative.
It can be difficult to differentiate between dementia and depression. Depression can manifest as dementia, or the dementia syndrome of depression (depressive pseudodementia) (Table 3). Conversely, dementia can present with depressive symptoms in the early stages of the illness. Depression and dementia, as well as many other illnesses in old age, may coexist. Up to 50% of individuals diagnosed with dementia will have coexisting depressive symptoms at some point in their illness.
Many medications can cause dementia-like states, including over-the-counter products. All medications should be carefully assessed and treatment ceased if appropriate.
Developed from scientific presentations at a special IPA meeting.
Sponsored by an educational grant from Pfizer Inc and Eisai Ltd.
International Psychogeriatric Association