How Is Parkinson’s Disease Diagnosed?

Parkinson’s disease is a neurodegenerative disorder that causes trembling, muscle rigidity, interrupted or slow movements, and postural problems, among other symptoms. It primarily affects those older than 60 and increases in severity over time. This condition can also impact memory, concentration, sleep quality, mood, and behavior.

Treated by neurologists (medical doctors who specialize in conditions affecting the brain and nervous system), the diagnosis of Parkinson’s disease primarily involves a neurological examination and medical history. Since the symptoms of this condition can resemble others, additional testing may be required to confirm suspected cases.

This article provides a quick look at how Parkinson’s disease is diagnosed, as well as what additional tests may be needed to confirm that diagnosis.     

Diagnostic Criteria

Parkinson’s disease diagnosis mostly depends on the neurologist’s ability to identify symptoms in a patient; aside from some genetic forms of the condition, there are no blood tests or imaging procedures that can diagnose the condition. However, this disorder has four characteristic or “cardinal” symptoms, the presence of which is often termed Parkinsonism. These include:

• Tremors: These are uncontrolled shaking movements that worsen when at rest or during activity. This tremor, which is usually seen in the hands—though the lips, legs, jaw, and tongue can also be affected—tends to be intermittent at first and becomes more prominent and chronic over time.
• Bradykinesia: This is when movements are slow or interrupted, something experienced clinically as fatigue, weakness, or lack of coordination. This issue creates a distinctive shuffling or interrupted gait, characterized by short, unsteady steps. Bradykinesia is seen at onset in 80% of cases and becomes a feature seen in nearly every case. 
• Rigidity: This is characterized as stiffness and resistance to passive movements of the limbs. It often occurs first on one side of the body and then eventually moves to the other. Rigidity arises in 75 to 90% of cases.
• Postural issues: Generally associated with more advanced cases, problems maintaining a normal, erect posture are another cardinal feature of Parkinsonism. This leads to trouble maintaining balance and coordinating movements.  

Individual presentations of Parkinson’s disease can vary. According to current recommended diagnostic standards by the International Parkinson and Movement Disorder Society (MDS), patients must display bradykinesia alongside resting tremors and/or rigidity in order to be diagnosed.

Supportive Symptoms and Red-Flags

Since other neurological disorders can also cause Parkinsonism, there are also supportive criteria for the condition, as well as certain “red flag” signs that may rule out the condition. 

Supportive criteria include:

• Reductions in symptoms after taking drugs that increase the neurotransmitter dopamine (dopaminergic drugs), such as Sinemet (levodopa)
• Increases in motor difficulties or interruptions with levodopa therapy as the medication wears off
• Tremor in a limb, either immediately observable or detected in a previous evaluation
• Loss of the sense of smell, known as olfactory loss
• Cardiac denervation, in which heart rate does not increase with rises in activity, something which is seen in using a form of imaging called Cardiac 123I-metaiodobenzylguanidine (123I-MIBG) scintigraphy

Several red flags and signs may indicate other issues; these are counterbalanced with supportive symptoms. The most common of these are:

• Very rapid progression of effects on gait, including an inability to walk within five years of symptom onset
• Early and rapid onset of severe dysphonia (an inability to speak or articulate) and dysphagia (an inability to chew properly)
• Inspiratory stridor, which is a whistling that occurs when inhaling
• Abnormally low blood pressure upon standing (orthostatic hypotension) within five years of symptom onset
• Rapid and early onset of severe urinary retention (also called urinary constipation) or incontinence (leaking urine on accident)
• Recurring falls—more than one a year—within three years of symptom onset
• Excessive anterocollis (repeated flexing of neck muscles) or flexion of hand or foot muscles within 10 years of symptom onset
• Absence of common nonmotor symptoms of Parkinson’s disease, such as insomnia, daytime sleepiness, urinary constipation or incontinence, inability to detect smells, depression, anxiety, or hallucinations within five years of symptom onset.

Lastly, there are several symptoms that outright exclude a Parkinson’s diagnosis, such as:

• Cerebellar abnormalities, such as cerebellar gait, characterized by widened stance, lateral unsteadiness, and irregular steps, as well as difficulties with oculomotor function (movement of the eyes)
• An inability to look up (supranuclear gaze palsy) and/or selective reductions in the ability to gaze downward
• Lack of response to levodopa therapy
• Current or recent treatment with a dopamine-blocking drug (dopamine antagonists)
• Loss of sensation and perception in the body, an inability to imitate actions (ideomotor apraxia), and an inability to express or comprehend written and spoken language (aphasia)

Medical History

An evaluation of your medical history and current status is essential for Parkinson’s diagnosis. In particular, neurologists focus on identifying symptom patterns and factors that may increase the risk for the condition. Generally, this means discussing:

• The intensity and duration of cardinal signs like tremors, bradykinesia, and rigidity
• Any nonmotor symptoms of Parkinson’s disease, such as sleep problems, mental health effects, and others
• Medications you’ve taken or are currently taking
• Prior history or current status of any diseases or medical conditions  
• Any family history of Parkinson’s disease
• Any history of exposure to pesticides, chemicals, or other environmental toxins that are risk factors for the condition

Neurological Exam

The physical examination for Parkinson’s disease—a neurological exam—screens for motor effects of the disease. Basically, this assessment tests coordination, strength, and overall ability to move. This involves:

• Tests of repetitive movement: The neurologist may ask you to perform repetitive movements, such as opening and closing a hand and tapping fingers or toes.
• Observation of spontaneous movements: Movement irregularities will also be observed as you’re seated, when you stand up, or while walking.
• Assessment for tremors: In order to screen for rest tremors—trembling when you are not moving—you’ll be observed as you remain still and focus on a specific task.  
• Checking for rigidity: The extent of any rigidity can be tested by pushing on a wrist or limb and feeling for resistance. This resistance tends to increase during voluntary movement.
• Gait assessment: You’ll be observed while walking down a hall or through a door to detect postural problems or any effects on motor coordination while walking.
• Pull test: This is an additional assessment of postural stability. It involves the neurologist pulling you back from behind while you’re standing to assess how well you retain balance and stance.

Genetic Testing

Generally, genetic testing is not a routine part of Parkinson’s diagnosis; however, it may help identify rarer inherited forms of the disease. Mutations or over-expression of certain genes, such as synuclein alpha (SNCA), parkin (PRKN), and PTEN-induced putative kinase 1 (PINK1) can be detected and imply a genetic case.

Screening for Related Conditions

One of the major challenges of diagnosing Parkinson’s disease is that this disorder can present similarly to other neurological disorders. Certain medications can also cause a similar set of symptoms, or they can arise as a result of other health conditions, something called secondary Parkinsonism. Among other possible diagnoses are:

• Essential tremor: Essential tremor affects both sets of hands and feet, head, voice, legs, and abdomen. This type of tremor differentiates from Parkinsonism because it occurs during motion or activity, as in while you’re holding your arms up or writing.
• Dementia with Lewy bodies: This common form of dementia is characterized by cognitive difficulties, hallucinations, and difficulties remembering and daily functioning, all of which can arise due to advanced Parkinson’s disease.
• Multiple system atrophy: This is a progressive neurological disorder that, in addition to impacting motor function, affects autonomic function, such as digestion, blood pressure, and urinary regulation. Earlier phases are often misdiagnosed as Parkinson’s disease.
• Corticobasal degeneration: This is a rare neurodegenerative disorder that causes an array of Parkinsonian motor symptoms, such as rigidity, tremors, lack of coordination, and others.
• Progressive supranuclear palsy: Early phases of this condition are known to closely mimic Parkinson’s disease symptoms. Therapy with levodopa may yield moderate effects, further complicating diagnosis.
• Fahr syndrome: This rare genetic disorder causes Parkinsonism, cognitive impairment, and involuntary muscle contractions, which cause repetitive twisting movements, among other symptoms.

In turn, secondary Parkinson’s disease—when symptoms arise due to other conditions—can be caused by:

• Head trauma
• Advanced Alzheimer’s disease
• Certain medications, such as the antipsychotic medications Serpasil (reserpine), Reglan (metoclopramide), and Stemetil (prochlorperazine)
• Exposure to toxins and certain chemicals, including carbon monoxide, manganese, and others
• Brain lesions caused by hydrocephalus (a buildup of fluids surrounding the brain), tumors, or brain bleed
• Metabolic disorders, such as end-stage kidney disease with diabetes, liver failure, and hypoparathyroidism (insufficient production of parathyroid hormone, which regulates calcium and phosphorous in the body)
• Neurogenetic disorders, such as Wilson disease and degeneration of neurons due to iron accumulation in the brain
• Certain infections, including encephalitis, human immunodeficiency virus (HIV), and others

While imaging and other tests have limited value alone to detect Parkinson’s disease, they can help rule out similar conditions or secondary cases. Methods that may be employed include:

• Magnetic resonance imaging (MRI): MRI of the brain relies on magnetic fields and computer-generated radio waves to generate images. This type of imaging may be used to detect hydrocephalus and tumors at the root of Parkinson’s-like symptoms.
• DaTScan: An iodine-based radioactive material is injected into the blood to assist with MRI or X-ray imaging. DaTScan tests can distinguish Parkinson’s disease from other neurological disorders, like essential tremor and multiple symptom atrophy.
• Positron emission tomography (PET) scan: PET scan relies on small amounts of radioactive material, known as a radiotracer, injected into the bloodstream. Using computerized imaging techniques, neurologists measure dopamine levels in the brain, which can differentiate Parkinson’s disease from some other neurological conditions.  
• Olfactory tests: Your sense of smell may be tested to help rule out other neurological conditions. This is because olfactory loss—the loss of smell—is a supportive sign of Parkinson’s disease and can rule other neurological diseases.

A Quick Review

Parkinson’s disease, a progressive neurological disorder that affects motor function, is primarily diagnosed through clinical evaluation and assessments of medical history. Neurological examination can test coordination, strength, and movement capability to detect the cardinal signs of the condition, which include tremors, bradykinesia (slow or interrupted movements), and rigidity. Imaging and other tests may be used to rule out other conditions that cause similar symptoms.