Clinical Features of Parkinson's Disease
Parkinson's disease is characterized by four cardinal motor symptoms: bradykinesia, resting tremor, rigidity, and postural instability, which appear after approximately 40-50% of dopaminergic neurons in the substantia nigra have been lost. 1, 2
Cardinal Motor Symptoms
- Bradykinesia: Slowness of movement and decreased amplitude of movement
- Resting tremor: Typically 4-6 Hz, asymmetric, and most prominent at rest
- Rigidity: Increased muscle tone throughout the range of passive movement
- Postural instability: Loss of postural reflexes, typically occurring later in disease progression 2, 1, 3
These motor symptoms result directly from dopamine deficiency in the striatum due to degeneration of dopaminergic neurons in the substantia nigra 1, 4.
Secondary Motor Symptoms
- Hypomimia (masked facies): Reduced facial expressiveness
- Speech abnormalities: Dysarthria, hypophonia (soft speech)
- Dysphagia: Difficulty swallowing
- Sialorrhea: Excessive drooling
- Micrographia: Small, cramped handwriting
- Gait disturbances: Shuffling gait, festination (acceleration of gait), freezing 3
- Dystonia: Abnormal sustained muscle contractions
- Glabellar reflex: Persistent blinking in response to tapping the forehead 3
Non-Motor Symptoms
Non-motor symptoms are increasingly recognized as significant contributors to disability and may appear before motor symptoms:
Autonomic Dysfunction
- Orthostatic hypotension
- Urinary urgency/incontinence
- Constipation
- Sexual dysfunction
- Excessive sweating 1, 3
Neuropsychiatric Features
- Depression
- Anxiety
- Apathy
- Cognitive impairment/dementia
- Hallucinations (especially with dopaminergic therapy) 3, 5
Sleep Disorders
- REM sleep behavior disorder (may precede motor symptoms by years)
- Excessive daytime sleepiness
- Insomnia
- Restless legs syndrome 3, 6
Sensory Abnormalities
- Anosmia (loss of smell): Often occurs years before motor symptoms
- Paresthesias
- Pain
- Visual disturbances 3, 5
Nutritional and Weight Changes
PD patients frequently experience weight changes during disease progression:
- Weight loss is common and associated with disease progression
- Increased energy expenditure due to rigidity and dyskinesias
- Dysphagia and gastrointestinal dysfunction contribute to nutritional challenges 2
Disease Progression and Complications
As the disease progresses, patients may develop:
- Motor fluctuations ("on-off" phenomena)
- Levodopa-induced dyskinesias
- Freezing of gait
- Falls
- Contractures in advanced disease
- Progressive disability requiring assistance with activities of daily living 1
Diagnostic Considerations
The diagnosis of PD is primarily clinical, as there is no definitive diagnostic test. Features that suggest diagnoses other than idiopathic PD include:
- Absence of rest tremor
- Early occurrence of gait difficulty and postural instability
- Early dementia or hallucinations
- Presence of dysautonomia early in disease course
- Ophthalmoparesis or ataxia
- Poor or no response to levodopa 3, 7
Clinical Pitfalls to Avoid
- Misdiagnosis of essential tremor as PD: Essential tremor typically occurs with action rather than at rest and has normal dopaminergic function 1
- Overlooking drug-induced parkinsonism: Medications that block dopamine receptors (particularly antipsychotics) can mimic PD symptoms 1
- Missing early non-motor symptoms: Symptoms like REM sleep behavior disorder, constipation, and anosmia may precede motor symptoms by years 5
- Underestimating nutritional impact: Regular monitoring of nutritional status and weight is recommended throughout disease course 2
Early identification of PD symptoms is crucial for timely intervention, although disease-modifying therapies remain an area of ongoing research.