Chapter 1: What is PD & Who Gets It?

Chapter 1: What is Parkinson’s Disease and Why do Some People Get it?

As we get started, let’s look at an overview of what you can expect to learn from this book. In order to implement optimal techniques and strategies to achieve maximum results in improving movement, cognitive function, and to reduce falls and fall risk, we must have an in depth understanding of all of the following:

  • What is Parkinson’s Disease (PD)?
  • Who gets Parkinson’s Disease?
  • What are some of the symptoms of PD? (both motor and non-motor symptoms)
  • How does PD affect strength, movement, mobility, ROM (range of motion), stability, balance, flexibility, cognitive function, emotions, and overall functionality?
  • What can people with PD be doing to manage disease symptoms and reduce or eliminate falls and injury
    • (how can caregivers, home health aides, and others help the person with PD to improve Quality of Life?)
  • As personal trainers, physical therapists, and coaches, what assessments and programming can be used to help people with PD to improve Quality of Life?

Throughout this book, you will read contributions from leading experts from the neurology, medical, and movement arenas. Our first contribution comes from Nick Sterling MD, PhD. I’m proud to say that Nick is my son and earned his PhD (and MD) at Hershey Penn State College of Medicine. He spent 2.5 years working on his PhD under the mentorship of a globally known and highly respected neurologist, Dr. Xuemei Huang. Below, Nick writes about “What is Parkinson’s and why is it significant?”

By Dr. Nick Sterling

What is Parkinson’s disease and why is it significant?

Every year, about 60,000 Americans are diagnosed with new-onset Parkinson’s disease and more than 10 million people worldwide are living with PD (Marras, 2016).  As a progressive neurodegenerative disorder, PD has no cure.  In developed nations, the lifetime risk of developing PD is approximately 1% for males and 0.5% for females. The disease process is marked pathologically by neuronal cellular degeneration within the brain and certain parts of the peripheral nervous system over a span of years. Classically, the symptoms of PD include tremor at rest, slowness of movement (bradykinesia), and muscle rigidity. As we will see in later chapters, the symptoms of PD are broad, especially in later stages, and can include many other motor, cognitive, and psychiatric manifestations at various points in the disease process.

Who gets Parkinson’s disease?

Currently, the risk factors and etiology of PD are under debate. It is thought that the risk of developing PD is a function of the interplay between genetic and environmental factors. There are several identified gene alleles that confer greatly increased risk of PD within certain families. However, these cases account for a very small fraction of PD incidence, and most associated genes have weak correlations with disease risk. Similarly, people who share particular environmental risk factors, such as chemical exposures, may have completely different outcomes. Therefore, the majority of PD cases are thought to be due to complex interactions between multiple genes and/or environmental factors. 

Despite our limited understanding of the mechanisms underlying PD, several characteristics have emerged as reliable risk factors that have been associated with higher rates of PD consistently across studies. First, increasing age is perhaps the most important factor. The average age of PD onset is approximately 65 years. It is possible, however, to develop PD at younger or older ages. Some patients, for example, may develop the disease in their early 40’s, although these cases are less common. Second, gender may play a role. For unknown reasons, PD affects males preferentially. Current theories regarding male predisposition include occupational exposures, hormonal effects, and other lifestyle factors. Third, there is some evidence suggesting that chemical exposures may contribute to PD. In particular, current research efforts are aimed at shedding light on the role of cumulative lifetime exposure to pesticides on the risk of developing PD. Past evidence has suggested that communities with higher rates of pesticide or well water usage have higher rates of PD. Animal studies suggest that some commonly used pesticides, such as paraquat, may be associated with similar pathology. Despite decades of research, however, PD is still a poorly understood process and the risk factors and mechanisms have not been fully elucidated.

How does PD start and evolve over time?

In order to understand how PD symptoms begin and then evolve over time, it is first helpful to look at the progression of pathology within the body. Currently, it is thought that PD pathology may begin in the most peripheral parts of the nervous system. These include innervated areas that are exposed to the external environment, such as the gut and the olfactory system. The vagus nerve carries fibers that connect the brain and the gastrointestinal system. It has several functions, such as controlling gastrointestinal motility, heart rate, and  information of the inner organs, such as gut, liver, heart, and lungs to the brain (Sigrid Breit, 2018). It has been suggested by some that the vagus may serve as an entry point for chemical toxins to disrupt and gain access to the central nervous system. Indeed, the vagus nerve does frequently show PD-related pathology on post-mortem studies. On a similar note, PD patients often develop difficulties with gastrointestinal motility, manifesting as constipation, and difficulty in regulating cardiovascular system. Orthostatic hypotension (dizziness when rising from a seated position) is common in PD and is thought to be due to impaired autonomic control of blood pressure. In the smell sensory system, the olfactory bulb is exposed to the external environment. The olfactory nerve carries communicating nerve fibers to the brain. These types of neurons, which are exposed to the external environment, are possibly serving on the “front lines,” which is perhaps why PD pathology shows up in these areas frequently. 

The earliest symptoms of the PD neurodegenerative process are subtle, but they are frequently detectable if one looks for them. Olfactory dysfunction is especially common in PD, and it may also be seen in other neurodegenerative disorders such as Alzheimer’s disease. The spouses or domestic partners of PD patients often report that the patient had not been able to smell various odors for many years leading up to a formal diagnosis. Also occurring in relatively early stages of PD, the midbrain and other areas of the brainstem begin to lose neurons due to cellular degeneration. Gait dysfunction is common, and frequently manifests as arm swing asymmetry and impaired limb coordination up to a decade before formal PD diagnosis. Sleep dysfunction may be another potential early manifestation, but its association is less clear at this time. Rapid eye movement sleep behavioral disorder is highly associated with future conversion to PD. Patients with this disease may act out their dreams and have sleep dysfunction. Given that they frequently convert to PD, it is possible that some of these patients may have been in “preclinical” stages of Parkinson’s disease. Similarly, it is common for PD patients to report disrupted sleep and short sleep duration.

By the time patients present to the physician complaining of resting tremor, slowness of movement, occasional falls, or rigidity, the PD pathologic process has likely been present for several years. At this point in the disease, the midbrain has been affected by neuronal degeneration already and there is likely to be just function of the basal ganglia.  Degeneration of dopamine-producing neurons within the substantia nigra pars compacta of the midbrain is the pathological hallmark of PD. This area of the brain normally supplies the basal ganglia with dopamine producing neurons to help control movements and some cognitive processes. However, at least 60-80% of the dopamine-producing neurons in this area are lost by the time that a typical patient presents to their physician with noticeable symptoms. 

PD used to convey a horrendous prognosis, with patients frequently dying in less than a decade after diagnosis. The discovery of dopaminergic drugs in the 1960’s, however, revolutionized PD treatment. These medications allowed many patients to live out the rest of their normal life expectancies with PD. More comprehensive therapeutic strategies are needed, however, since PD eventually affects most brain areas in addition to dopamine-producing areas. Along with widespread brain degeneration, dopaminergic drugs can have serious and permanent adverse effects. When patients start dopaminergic medication, there is often a “honeymoon” period. For a period of roughly five years, the patient may experience dramatic improvement of symptoms. After this time, the patient may begin to require higher and higher doses of dopaminergic drugs, along with other pharmacologic agents. These symptoms, such as hallucinations, can be due to the direct effects of dopamine on neurons. Other adverse effects, such as dyskinesia, are thought to be due to long-term neural adaptation to dopamine. Dyskinesia is common in later stages and may manifest as involuntary and uncoordinated movements, often of the extremities. For these reasons some physicians in the past have advocated to delay dopaminergic treatment until it is absolutely necessary, but this topic is still under some debate. 

Deep brain stimulation is becoming a popular method of treating PD, since it avoids the adverse effects of medication. However, there is some data to suggest that patients with deep brain stimulation of the subthalamic nucleus have higher rates of falls. It is currently unclear whether the increased risk of falls is attributable to subthalamic stimulation itself or simply from improvement of bradykinesia and increased daily activity. Other forms of deep brain stimulation, such as that targeting the globus pallidus internus or pedunculopontine nucleus, are currently being researched and are beyond the scope of this program.

What is the everyday experience of a client with PD?

Although uncontrolled tremor may appear to an observer to be a particularly uncomfortable manifestation of the disease, rigidity and slowness of movement are reported by patients to be the most significant symptoms impacting quality of life. Patients with more severe rigidity and bradykinesia tend to have disproportionately worse long-term prognoses, compared to those with severe tremor. Cognitive symptoms are especially common in bradykinesia- and rigidity-predominant patients. Such symptoms are thought to arise from severe dysfunction of the basal ganglia. Widespread brain degeneration, however, likely contributes to broad neurological symptoms such as frequent falls, depression, executive dysfunction, impaired memory, and eventually dementia. 

When working with a client who has PD, it is important to realize that motor symptoms are only the most obvious outward manifestation of a complex internal disease process. The client might be dealing with any number of additional issues as PD progresses, such as depression, sleep dysregulation, autonomic disturbances, and medication side effects.

Why are physical and mental exercise important in Parkinson’s disease?

While medication targeting neurotransmitters in the central nervous system is the mainstay of therapy, trainers may bring additional tools to help improve life for these clients. There is a sizeable body of literature suggesting that physical and mental exercise may have beneficial and potentially long-lasting effects on the quality of life, function, and medication requirement of patients with PD. 

For example (Margaret K. Mak, 2017):

  • Most progressive strength and aerobic endurance training programmes have positive effects that last for 12 weeks
  • Extended progressive strength training improves muscle strength for up to 24 months and aerobic endurance training increases walking capacity at 6–16 months
  • Balance training improves balance, gait and mobility, and reduces falls for up to 12 months after completion of treatment
  • Gait training improves gait performance and walking capacity for up to 6 months after training
  • Tai chi and dance improve balance and tai chi reduces fall frequency up to 6 months after training
  • A training period of at least 6 months is effective for achieving clinically meaningful improvement in UPDRS-III scores

This book represents an important step forward for patients with PD to engage in their own health and wellness. Moreover, it may serve as a tool to arm trainers with awareness and information to combat the functional decline that occurs with PD progression, as well as improving quality of life for patients. While a sizeable body of literature suggesting that exercise is effective for achieving these aims, there is currently no single defined collection of “best” or “standard” exercises. We are at an exciting stage of understanding how trainers and physical therapists can help clients with PD. Accordingly, the programs outlined in this book should be taken as concepts largely based on current research literature. They may serve as a framework for developing training programs that are tailored to the individual needs of clients. In coming years, research may shed light on optimal physical and mental exercise practices in PD. As this literature evolves, future versions of this volume will be updated to reflect these changes. We hope that the information contained within this book, when applied in a safe setting with proper medical oversight, may facilitate you in better understanding PD and conceptualizing training programs that may improve quality of life.

Thank you for that insightful input, Dr. Nick!

For those (like myself) who like visuals, figure 1.1 gives you a look at the brain and shows the location of the substantia nigra. In the images to the right, you’ll see the difference between the appearance of a healthy substantia nigra and one that represents what would be seen in Parkinson’s.

Figure 1.1

Figure 1.2 again shows differences we see between a normal brain and a brain with PD. Notice the darker portion of the substantia nigra on the image on the left (normal) vs. the image on the right (Parkinson’s). You’ll also see a more solid nigrostriatal connection (illustrated by red lines) in the image on the left.

Figure 1.2

Lastly, in figure 1.3, we see results from a DaTscan. DaTscans were approved by the FDA in the USA in 2011 to help better diagnose Parkinson’s and other disorders. In a DaTscan, the patient is injected with a radioactive tracer called Iofluplane. During a period of a few hours after injection, the DaTscan attaches to the dopamine transporters. After a few hours, special imaging equipment is used to scan and create images of what is seen in the brain. In figure 1.3 on the left, you’ll notice a well illuminated nigrostriatal area representing a normal, healthy dopamine system. On the right, you’ll see an image of a Parkinson’s like and unhealthy dopamine system.

While the DaTscan is helpful in telling us what’s going on in the brain, it’s not a sure way of diagnosing PD. Imaging as seen in figure 1.3 could possibly represent other disorders such as Multiple system atrophy (MSA), Progressive supranuclear palsy (PSP), or Corticobasal ganglionic degeneration (CBGD). The DaTscan will not distinguish between these disorders.

Figure 1.3