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| PET SCAN |
The human brain might be perceived as
an organ with two main strategic tasks: goal-directed motor behavior, and
mental functioning in order to work out that goal. These two main functions
have two prototypical diseases: Alzheimer disease, in case of mental function,
and Parkinson’s disease, with motor function.
Following its inception as an entity,
Parkinson’s disease (PD) was long perceived to be a purely motor disorder with
unimpaired mental functions. This was partly influenced by its initial
description by James Parkinson,
who wrote that the intellect and senses remain intact. Although some of
his contemporaries challenged this view and suggested that mental functions do
get impaired in patients with advanced PD, this observation did not receive
much attention for many decades. It’s ironic that modern medical treatment,
which has dramatically changed the lives of PD patients, came as a mixed blessing;
trading effective management of motor symptoms and longer patient survival with
mental dysfunction (and some other non-motor features of the disease) becoming
more apparent.
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Front and side views of a man portrayed to be suffering from Parkinson’s disease. These are woodcut reproductions (of two collotypes from Paul de Saint-Leger’s 1879 doctoral thesis, Paralysie agitante etc.) published in Gowers, William Richard (1886). Public domain via Wikimedia Commons. - See more at: http://blog.oup.com/2015/05/dementia-parkinsons-disease/#sthash.r1AnVHEq.dpuf
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Research in the last few decades has
established that cognitive impairment and dementia are an integral part of the
disease process. Several prospective as well as cross-sectional studies
revealed that milder forms of cognitive impairment can even be detected at the
early stages of the disease, if appropriately looked for. In fact, it has
become apparent that some non-motor symptoms may precede classical motor
symptoms by many years, such as anosmia, depression, constipation and
dream-enacting behavior. When properly assessed, a variety of non-motor
symptoms can be identified throughout the disease. Dementia develops
particularly in patients with advanced age and severe disease; twenty years
after the diagnosis, mental dysfunction of varying degrees is present in
practically all patients.
In earlier years the assumption was
that dementia in PD may simply represent co-incident Alzheimer disease (AD).
Research on the profile of dementia associated with PD (PD-D), however,
demonstrated that, in a typical patient, its features are different than that
of AD, and it constitutes a dementia syndrome of its own. Biochemical deficits
and pathological features associated with PD-D were also worked out, which lead
to the first rationally designed treatment trials. These studies bore fruit and
the first specific drug for PD-D became available. In parallel, clinical
diagnostic criteria were described for PD-D as well as criteria for mild
cognitive impairment associated with PD (PD-MCI). Efforts are now ongoing to
better understand the neurobiological basis of cognitive impairment and to find
biomarkers which can identify patients at risk in earlier stages. Once the
chrono-biology of mechanisms are better understood, scientists may be able to
design treatment interventions to halt the progression of mental dysfunction,
as well as the progression of the disease itself.
We have entered a new phase in
Parkinson’s disease research: its molecular pathology is being disentangled;
the first vaccination trial is on the way along with efforts to in vivo image
the accumulation of alpha synuclein molecules, the hallmark pathological
feature of PD. We are looking forward to exciting times, which we hope to come
sooner rather than later.
Featured image: PET image by Jens Maus. Public domain via Wikimedia
Commons.
Murat Emre is Professor of Neurology
at the Istanbul Faculty of Medicine, Istanbul University, where he chairs
The Behavioral Neurology and Movement Disorders Unit. His research
interests are in Parkinson's disease and related disorders, in particular
cognitive aspects of the disease, Alzheimer's disease and related dementias. He
is editor of Cognitive
Impairment and Dementia in Parkinson's Disease, Second Edition.
- See more at:
http://blog.oup.com/2015/05/dementia-parkinsons-disease/#sthash.r1AnVHEq.dpuf
http://blog.oup.com/2015/05/dementia-parkinsons-disease/
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