Lewy bodies are clumps of abnormal proteins found within brain cells. Lewy bodies can only be seen in autopsies, and have been found in the brains of Parkinson's patients who had dementia symptoms, patients who had a dementia similar to Alzheimer's and patients who had distinct dementia symptoms. The exact relationship between the Lewy bodies, Parkinson's, Alzheimer's and dementia itself is uncertain. The characteristics of the final stage of Lewy body dementia will depend on whether it most resembles Parkinson's, Alzheimer's or distinct Lewy body dementia.
Dementia With Parkinsonia Features
Lewy bodies are found in the brains of many patients who had Parkinson's disease, but not all of these patients had dementia. However, most Parkinson's patients who did have dementia were found to have Lewy bodies at autopsy. Whether a patient is diagnosed with Parkinson's disease with dementia or Lewy body dementia with Parkinsonian features depends, somewhat arbitrarily, on when the dementia symptoms first appear relative to the movement problems characteristic of Parkinson's disease. So some patients diagnosed with Lewy body dementia may in fact have fairly severe Parkinsonian symptoms that dominate the final stage. These symptoms include a shuffling gait, tremors when not moving, problems with balance and posture, and rigid or "frozen" muscles that make movement difficult. Typically, these symptoms worsen until the patient can no longer perform self-care activities and eventually becomes bed-bound.
Alzheimer's Variant
Patients who had Alzheimer's disease also have abnormal structures, called amyloid plaques, inside their brain cells at autopsy. In addition to the amyloid plaques, some patients who had Alzheimer's disease have also been found to have Lewy bodies. This finding has lead to the notion of an "Alzheimer's variant" of Lewy body dementia, or perhaps a "Lewy body" variant of Alzheimer's. Patients in the final stage of the Alzheimer's variant of Lewy body dementia display some of the distinct Lewy body characteristics described below, but Alzheimer-like symptoms predominate. These include confusion, aggression, disorientation and loss of short-term memory, judgment and inhibition. Delusions are common, but they are usually non-bizarre and may be a consequence of profound memory loss. A common delusion, known as Capgras Syndrome, involves the belief that a caretaker has been replaced by an impostor. In the very late stages, a Parkinson's-like muscular rigidity may develop, but tremors are usually absent.
Distinctive Lewy Body Symptoms
Because all dementias share some features in common, patients in the final stage of Lewy body dementia will display some of the characteristics of Alzheimer's disease described above, but in the non-Alzheimer's variant certain distinctive symptoms are more prominent. The most notable of these symptoms are hallucinations and bizarre delusions, involving such things as elaborate conspiracies or supernatural forces. Patients sometimes display Capgras syndrome, but in contrast to the Alzheimer's variant, it is typically present from the early stages of the disorder. Confusion and disorientation are also features of Lewy body dementia, although rather than being continual, as in Alzheimer's, they often fluctuate with periods of relatively clear thinking. Patient's with Lewy body dementia often display little short-term memory loss in the early stages of the disorder, although by the final stage there is usually some degree of memory disturbance. Patients with dementia as their primary complaint will also frequently have some degree of Parkinsonian movement symptoms in the final stage, although these usually will not be as severe as those seen in patients diagnosed primarily with Parkinson's disease.
References
- "Pathologic Basis of Disease"; Vinay Kumar, et al. (eds.); 2005
- "Harrison's Principles of Internal Medicine"; Dennis L. Kasper, et al. (eds.); 2005
