Cardinal Features of Parkinson's Disease
The cardinal features of Parkinson's disease are resting tremor, bradykinesia, rigidity, and postural instability, which result from progressive degeneration of dopaminergic neurons in the substantia nigra projecting to the striatum. 1
Primary Motor Symptoms
- Resting tremor: Characterized by rhythmic, oscillatory movements that occur when the affected body part is at rest and typically diminishes with voluntary movement 2
- Bradykinesia: Slowness of movement and progressive reduction in speed and amplitude of repetitive actions, representing one of the most disabling features of PD 1
- Rigidity: Increased resistance to passive movement of limbs, which may present as "lead-pipe" (uniform) or "cogwheel" (ratchet-like) resistance 2, 3
- Postural instability: Loss of postural reflexes leading to impaired balance and increased risk of falls, typically appearing later in disease progression 1, 4
Clinical Presentation and Diagnosis
- PD is the most common parkinsonian syndrome, with peak onset between 60-70 years of age 1
- Motor symptoms typically appear asymmetrically and progressively worsen over time 2, 4
- Symptoms typically manifest after approximately 40-50% of dopaminergic neurons in the substantia nigra have been lost, with an estimated 5-year interval between initial neuronal loss and symptom appearance 1
- Diagnosis is primarily clinical, as there is no definitive diagnostic test for PD 2, 5
Secondary Motor Features
- Hypomimia (masked facies) 2
- Dysarthria and dysphagia 1
- Micrographia (small handwriting) 2
- Shuffling gait, festination (involuntary acceleration while walking), and freezing 2
- Dystonia 2
- Sialorrhea (excessive drooling) 1
Non-Motor Features
While not cardinal features, these are increasingly recognized as important components of PD:
- Autonomic dysfunction: Including gastrointestinal dysmotility, gastroparesis, constipation, and urinary incontinence 1
- Cognitive impairment and dementia: Especially in later stages 1, 6
- Neuropsychiatric symptoms: Depression, anxiety, apathy, and psychosis 1, 6
- Sleep disorders: Including REM sleep behavior disorder, which may precede motor symptoms 3, 6
- Sensory abnormalities: Anosmia (loss of smell), paresthesias, and pain 2, 3
- Fatigue: A common and disabling symptom 4
Differential Diagnosis Considerations
- Absence of rest tremor, early gait difficulties, early postural instability, early dementia, hallucinations, dysautonomia, ophthalmoparesis, or ataxia may suggest diagnoses other than idiopathic PD 2
- Poor or no response to levodopa therapy should prompt reconsideration of the diagnosis 2, 4
- Other parkinsonian syndromes to consider include Progressive Supranuclear Palsy (PSP), Multiple System Atrophy (MSA), and Corticobasal Degeneration (CBD) 1
Clinical Progression
- PD is a progressive neurodegenerative disorder with increasing disability over time 6
- As the disease advances, axial symptoms and non-motor features become increasingly prominent and often less responsive to dopaminergic therapy 6
- Weight loss is common and associated with disease progression due to increased energy expenditure from dyskinesias and rigidity 1