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Experts in movement disorders and dementia have long debated the relationship between dementia with Lewy bodies (DLB) and Parkinson’s disease with dementia (PDD). But a new consensus was recently published in Neurology, the journal of the American Academy of Neurology that should ultimately translate into increased research and knowledge for Lewy body dementias. Led by Dr. Carol Lippa (chair of LBDA’s Scientific Advisory Council) and international experts in PD and DLB, the consensus came out of deliberations held after the 2006 landmark conference “PDD/DLB at a Crossroad” in Washington, DC.
As the second most common type of dementia behind Alzheimer's disease, DLB shares numerous clinical and biological features with PDD. In fact, upon autopsy, the two disorders are difficult to distinguish without accompanying clinical records that document the course of the disorder. As there is no principal symptom that clearly differentiates PDD from DLB, clinicians and researchers have been using the common convention of the “one year rule”. This rule indicates that when the motor symptoms begin more than a year before dementia, a diagnosis of PDD is given. When these two symptoms begin within the same year or if the motor symptoms start after the cognitive changes, then a diagnosis of DLB is given.
Research from autopsied brains of patients with DLB, PDD and Parkinson’s disease without dementia (PD) has shown distinctive microscopic abnormalities inside nerve cells (neurons) called Lewy bodies, whose main component is a protein called alpha-synuclein. As a result, the new consensus among experts is to refer to all three disorders as “Lewy body disorders.” By classifying multiple conditions into a single group, research can be more easily facilitated due to the similarities in the biology of the conditions. In a clinical setting, particularly when dementia is evident, patients and families may find it convenient to use the term PDD if motor symptoms occur first and DLB if cognitive symptoms occur first or concurrently, according the one year rule. However, in a research setting, the recommended term for encompassing both PDD and DLB is “Lewy body dementias.”
Experts also agree that genetic factors play a role in PD, PDD and DLB, although the extent of the role currently only explains a small proportion of cases. Moreover, unlike other neurological conditions such as Huntington's disease, there is no clearly defined, testable genetic abnormality that can accurately predict the development of, or distinguish between PDD and DLB.
Medical imaging technologies such as MRI and PET may be useful in distinguishing DLB and PDD from other neurodegenerative disorders. However, current imaging research has not led to improved ability to discriminate between PDD and DLB.
The new consensus establishes goals for improving the understanding and treatment of PDD and DLB. This includes continued collaboration between clinicians and researchers focusing on motor and cognitive abnormalities, better identifying the differences in the brain between the two groups, and finding new treatment options. Additional research designed to shed further light on the relationship between PDD and DLB includes identifying genetic and environmental risk factors that make a person susceptible to the disease, and improving our understanding of the biological mechanisms responsible so that preventative or curative therapies can be developed.