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Parkinson’s Disease: Testing and Diagnosis

As individuals grow old their susceptibility to disease increases. Impairments in the nerves and muscles can occur, but the widespread changes that happen with aging can make a diagnosis of these impairments difficult.  For example, in Parkinson’s disease, a disease of the nervous system that influences movement control, a medical specialist must assess many symptoms that could overlap with other disorders. As research becomes more advanced and technology continues to develop, however, accurate diagnoses are possible.

Parkinson's disease diagnosis

Importantly, diagnosing Parkinson’s disease early on is important for patient outcomes. Parkinson’s disease progresses over time. Therefore, an early diagnosis is important to increase the patient’s quality of life and to delay its progression.

Diagnosing Parkinson’s Disease

Parkinson’s disease must be diagnosed by a medical professional, but research is making this easier and more accurate. Diagnosis can also be made by performing an autopsy after an individual has passed away.

Parkinson’s disease diagnosis is based on phases created by the Motor Disorders Society. These are the three phases of Parkinson’s disease:

  1. Preclinical phase: In this phase, the patient does not show any signs or symptoms of Parkinson’s disease, but changes are starting to take place in the nervous system.
  2. Prodromal phase: Here, signs and symptoms are beginning to show. This usually includes mild movement-related and non-movement-related symptoms. In the prodromal phase, a diagnosis can be very challenging to make. therefore it is important that the medical professional performs a detailed study of risk factors, and signs and symptoms.
  3. Clinical phase: In this phase, the signs and symptoms of Parkinson’s disease become obvious and the medical professional is usually able to make an accurate diagnosis. Clinical diagnosis requires a detailed exam of the patient in order to distinguish Parkinson’s disease from other, similar diseases.

Risk Factors for Parkinson’s Disease

Risk factors for Parkinson’s disease include age, sex, family history, head trauma, and exposure to toxins, among others. In terms of age, Parkinson’s disease is more prevalent in those over 60 years of age. Males are more likely to develop Parkinson’s disease than females. For every three males that develop it, only two females do. Head trauma is another important risk factor.

Some of these risk factors should be looked at carefully when making a diagnosis. Many patients diagnosed with Parkinson’s disease do not have a family history of the disease. However, having a family member with Parkinson’s disease may increase your risk of developing the disease by three due to genetic differences. While exposure to toxins can increase your risk, they cannot cause Parkinson’s disease alone. Some toxins that can have an effect on the nervous system are organophosphates and rotenone, among several other chemicals.

Apart from risk factors, there are also “protective factors” that could protect from developing Parkinson’s disease. These include caffeine, antioxidants, alcohol, and smoking. “Protective factors” is placed between quotation marks because there is not enough research to support these claims.

Signs and Symptoms of Parkinson’s Disease

A physician can attempt to diagnose Parkinson’s disease beginning in the prodromal phase. However, it is important to emphasize that diagnosis in this phase is very rare because certain signs and symptoms typically appear in the clinical phase.

Symptoms can be classified as movement-related (motor) and non-movement-related (non-motor). The non-motor manifestations include olfactory dysfunction, sleep alterations, and mild autonomic symptoms.

Olfactory dysfunction is one of the most studied symptoms in terms of Parkinson’s disease diagnosis and refers to difficulties with the sense of smell. Olfactory dysfunction is called either hyposmia or anosmia. Hyposmia is a partial dysfunction, while anosmia is a complete loss of smell. The degree of hyposmia can also be identified as “severe”, “moderate” or “mild. This is one of the most common symptoms of Parkinson’s disease (60-90% of prevalence). However, it is important to note that olfactory dysfunction alone does not indicate Parkinson’s disease, and patients with this sign do not necessarily develop any kind of Parkinson’s disease-related processes.

Clinical evaluation of olfactory dysfunction can be done through a look at the patient’s history or more objectively through several tests and measures, which include the University of Pennsylvania Smell Identification Scale or the Phenyl Ethyl Alcohol or Detection Threshold. The University of Pennsylvania Smell Identification Scale requires the patient to smell and identify 40 items. They are scored on a range from 0 – 40 and compared to results from others in the same age and gender group.

Other symptoms that can be used to guide a diagnosis are sleep disorders, such as rapid eye movement behavior disorder. Rapid eye movement behavior disorder is the presence of violent dreams, vocalization, loss of muscular relaxation, and dangerous behaviors during sleep. In contrast to olfactory dysfunction, rapid eye movement behavior disorder is very indicative of neurological degeneration. Those with rapid eye movement behavior disorder have a 50-70% risk of being diagnosed with a neurodegenerative disease and a 38% risk of being diagnosed with Parkinson’s disease.

Like olfactory dysfunction, Rapid Eye Movement behavior disorder can be identified through the patient’s history or medical tests. Medical testing is done through polysomnography. The results of the polysomnography will show abnormal muscle activity during sleep.

Autonomic changes are also seen in Parkinson’s disease, including constipation. Interestingly, constipation is one of the first symptoms to appear when one develops Parkinson’s disease; it can appear from 2 to 24 years before the onset of the disease. One must be aware, however, that constipation does occur frequently across individuals and it is rarely indicative of Parkinson’s disease.

Motor signs can be key to identifying patients who are developing Parkinson’s disease, especially in the prodromal phase. The presence of micrographia, which is defined as smaller than normal handwriting, has been used to help diagnose Parkinson’s disease for many years. Furthermore, changes in size, duration, speed, and fluency of handwriting can all be used to determine changes in handwriting.

Criteria for Parkinson’s Disease Diagnosis

By the time the patient has reached the clinical phase, many signs and symptoms become very apparent. Criteria for Parkinson’s disease diagnosis are typically used to make a diagnosis.

First, the clinical signs and symptoms must develop in a progressive manner, meaning that they should increase in severity over time. If they are not progressive, they could point to another disease that is more acute, or short-lived.

Additional cardinal signs and minor signs are used in diagnosing Parkinson’s disease. The exact number of signs needed from each category varies, yet the signs assigned to each group remain the same. All cardinal signs of Parkinson’s Disease are motor signs and include the following: bradykinesia, resting tremor, cogwheel rigidity, and postural instability. Minor signs include both motor and non-motor signs, such as hypophonia, drooling, olfactory dysfunction, autonomic changes, and neuropsychiatric manifestations.

Excluding Other Diagnoses

During an evaluation, the physician should consider excluding criteria that might suggest another diagnosis. For example, if a patient presents with Parkinson’s disease signs and symptoms along with early dementia and hallucinations, this may suggest Dementia with Lewy Bodies.

Other exclusion criteria include supranuclear gaze palsy, abnormal imaging results, or a history of repeated strokes. One of the most important exclusion criteria is no response to taking the medication levodopa. Parkinson’s disease is highly responsive to levodopa, therefore if a patient does not respond to this medicine then they might investigate for a different diagnosis.

Severity of Parkinson’s Disease

After diagnosing a patient with Parkinson’s disease it is useful to evaluate its severity. Numerous scales have been developed to quantify disease severity.

One of the most commonly used scales is the Unified Parkinson’s Disease Severity Scale, which is a 199-point scale. Points are added from three different sub-scale. The final score indicates the severity, which ranges from 0 (meaning no disability) to 199 (total disability). Other scales for evaluating severity include the Webster Parkinson’s Disease Scale and the Parkinson’s Disease Activities of Daily Living Scale.

Testing for Parkinson’s Disease

For many diseases, physicians can rely on a variety of testing techniques to confirm a diagnosis. This is not the case with Parkinson’s disease, as testing technology is not as useful. Physicians must mainly rely on clinical evaluations. However numerous studies are being performed on imaging techniques, biological markers, and mechanosensor technologies that can be used to diagnose Parkinson’s disease.

Imaging is one of the more recent developments in Parkinson’s disease testing. Currently, research is focused on functional imaging technologies (PET and SPECT), MRI, and transcranial sonography.

  • Functional imaging technology can measure the function of nervous system cells that are involved in Parkinson’s disease. Parkinson’s disease is characterized by low levels of dopamine, and the nervous system cells that produce dopamine are examined by functional imaging technology.
  • Transcranial sonography can also be used to help assess for Parkinson’s disease. This type of imaging can identify changes in parts of the brain that are related to Parkinson’s disease. Transcranial sonography cannot assess the severity of the disease, however.
  • MRI technology is used to identify diseases in patients that exclude the diagnosis of Parkinson’s disease.  In regular MRI studies, evidence of secondary causes of Parkinson’s disease can be found, such as hydrocephalus, neoplasms, granuloma, or traumatic brain injury.

Another testing technology currently being developed is the use of biological markers. Biomarkers could be used in studying at-risk patients in the preclinical or prodromal phases. They could also be used as a tool to diagnose in the clinical phase.

These markers are extracted from body fluids such as urine, blood, or cerebrospinal fluid. However, biological markers from the cerebrospinal fluid are thought to be of greater value due to their location in the body. Biomarkers include a wide range of biological molecules, such as alfa-synuclein protein, DJ-1 protein, inflammatory markers, and many more that are related to the development of Parkinson’s disease.

Finally, a new technology that is at the forefront of Parkinson’s disease diagnosis is the use of a mechanosensor. In an attempt to identify changes in movement as early as possible, many devices are being developed such as this wearable technology. This includes keyboard tests, gait sensors, voice analyzers, and many more. These tests attempt to gather information about changes in movement that only become apparent after the disease has progressed.


These tools in Parkinson’s disease diagnoses seek to identify abnormal findings in patients to aid in an early diagnosis. However, it is important to consider the practicality and cost of each.  Functional studies are not widely used in medical facilities and are quite expensive. In contrast, mechanosensor technology could be relatively cheap to implement. While there is no cure for Parkinson’s disease, recent research and technological advancements have allowed for a more clear diagnosis and better outcomes for those that develop this disease.