Parkinson’s disease is a progressive neurological disorder characterized by three primary motor symptoms: tremor, rigidity, and bradykinesia (slowness of movement). These three hallmark signs are considered the main clinical features that allow doctors to diagnose Parkinson’s disease.
Tremor
Tremor is the most well-known and easily recognizable symptom of Parkinson’s disease. It is present in around 70% of Parkinson’s patients. Tremor associated with Parkinson’s usually starts in the hand, finger, or thumb on one side of the body. It consists of unintentional rhythmic muscle contractions that alternate between contraction and relaxation, resulting in trembling or shaking movements. The tremor typically occurs at rest and disappears with action or movement. It usually begins unilaterally (on one side of the body) and tends to affect the distal part of the limb (hands rather than arms). The tremor also tends to worsen as symptoms progress over time.
There are several distinguishing features of Parkinsonian tremor:
- Resting tremor – occurs when the limb is at rest and improves with action
- Unilateral onset – starts on one side of the body
- “Pill-rolling” fingers – tremor of hand may involve repetitive rotating movements of the fingers
- Frequency of 4-6 Hz – relatively slow, regular, rhythmic tremor
- Improves with sensory tricks – such as touching the thumb to the index finger
Parkinson’s tremor can be very slight at onset but often worsens over time. Typically, the tremor is most pronounced at rest and is greatly reduced with action. However, as the disease progresses, tremor can become more persistent and appear during voluntary movements.
Rigidity
Rigidity refers to stiff or inflexible muscles associated with increased muscle tone and resistance to passive movement. Around 90% of Parkinson’s patients experience rigidity. When a doctor examines a Parkinson’s patient, they will check for rigidity by passively moving the patient’s joints and limbs. If rigidity is present, the doctor will feel a constant resistance, like moving a stiff lever, as they flex and extend the patient’s arms, legs, fingers, and wrists.
Signs and symptoms of rigidity include:
- Stiffness and inflexibility of the muscles
- Tightness of the limbs, neck, and trunk
- Aching or cramping pain due to muscle stiffness
- Resistance to passive movement of the joints
- Difficulty performing everyday tasks due to stiffness
Rigidity can occur in almost any muscle in the body but tends to affect the neck, shoulders, and limbs. Like tremor, rigidity also commonly begins unilaterally on one side of the body and eventually spreads to both sides as the disease progresses. Rigidity is often accompanied by joint pain caused by the constant muscle stiffness.
Bradykinesia
Bradykinesia refers to the slowness of movement that is characteristic of Parkinson’s. It affects the performance of voluntary movements, causing difficulty initiating movement and slowing down speed and amplitude of repetitive actions. Bradykinesia is present in the majority of Parkinson’s patients and occurs due to dysfunction in the basal ganglia that impairs the brain’s ability to regulate the force and speed of movements.
Signs and symptoms of bradykinesia include:
- Slowed movements and reaction time
- Difficulty initiating or spontaneous movements
- Progressive loss of fine motor skills
- Reduced arm swing when walking
- Smaller handwriting (micrographia)
- Monotonic, hypophonic dysarthria (slow, quiet, and mumbled speech)
- Loss of facial expression (hypomimia)
Bradykinesia can make everyday tasks requiring fine motor control very difficult. Actions such as buttoning a shirt, cutting food, or rising from a chair become increasingly challenging. Patients often report that they have trouble keeping up with the pace of normal conversation or activities because of slowed movements.
Putting It All Together: The Parkinson’s Triad
In summary, the three cardinal motor signs of Parkinson’s disease are rest tremor, rigidity, and bradykinesia. Together, these three symptoms are known as the “Parkinson’s triad”. The combined presence of at least two out of these three manifestations is strongly indicative of Parkinson’s disease diagnosis.
Here is an overview of the Parkinson’s triad:
| Motor Symptom | Description |
|---|---|
| Tremor | Resting tremor that begins unilaterally, 4-6 Hz pill-rolling tremor of hands |
| Rigidity | Stiffness and resistance to passive movement of limbs and joints |
| Bradykinesia | Slowness of voluntary movements with progressive loss of fine motor control |
Although not considered cardinal features, several other motor symptoms commonly occur in Parkinson’s:
- Postural instability – impaired balance and coordination
- Freezing of gait – brief episodes of inability to step forward while walking
- Hypokinesia – decreased amplitude of movements
- Shuffling gait – short stepped, shuffling walk with stooped posture
Non-Motor Symptoms
In addition to the primary motor symptoms, Parkinson’s disease involves many non-motor features that can precede motor symptoms by years or even decades. These include:
- Loss of smell (hyposmia)
- REM sleep behavior disorder
- Mood disorders – depression, anxiety
- Cognitive impairment and dementia
- Autonomic dysfunction – constipation, orthostatic hypotension
- Fatigue
- Pain
While many patients and physicians focus on the motor impairments of Parkinson’s, recognizing the extensive non-motor elements is equally important for diagnosis and monitoring progression. The non-motor symptoms of Parkinson’s can be as disabling as the motor symptoms in many patients.
Diagnosing Parkinson’s Disease
There are no laboratory tests that can definitively confirm Parkinson’s disease. Diagnosis relies on a physician’s clinical examination, evaluation of symptoms, and medical history. The UK Parkinson’s Disease Brain Bank criteria are often used to diagnose Parkinson’s:
- Bradykinesia
- Plus one of the following:
- Muscular rigidity
- 4-6 Hz rest tremor
- Postural instability
- No exclusion criteria present that point to alternate causes
- Three supportive criteria present:
- Unilateral onset
- Rest tremor
- Progressive disorder
- Persistence of symptoms >3 years
- Levodopa responsiveness for ≥5 years
- Clinical course of ≥10 years
Neuroimaging and laboratory tests may be used to rule out other disorders that could mimic Parkinson’s disease. Response to levodopa and dopamine agonists can also help confirm Parkinson’s diagnosis in equivocal cases. However, there are no definitive tests – diagnosis relies heavily on a skilled clinician’s examination and observation of the core Parkinson’s motor symptoms.
Conclusion
The three hallmark symptoms of Parkinson’s disease are resting tremor, rigidity, and bradykinesia. This triad of motor impairments forms the basis for clinical diagnosis, along with supportive criteria such as unilateral onset, progression over years, and levodopa response. Tremor is the most recognizable feature, but rigidity and bradykinesia occur in the vast majority of PD patients. Non-motor symptoms are also important to recognize. While there are no definitive laboratory tests for Parkinson’s, observation of the characteristic progressive motor symptoms remains the gold standard for diagnosis.