What is the approach to diagnosing parkinsonism?

Diagnosis of Parkinsonism

The diagnosis of parkinsonism is primarily clinical, requiring the presence of bradykinesia (the essential feature) plus at least one of the following: resting tremor, rigidity, or postural instability, with I-123 ioflupane SPECT/CT (DaTscan) serving as the definitive imaging test when clinical diagnosis is uncertain. 1, 2

Essential Clinical Diagnostic Criteria

Cardinal Motor Signs Required for Diagnosis

• Bradykinesia is mandatory - this slowness of movement must be present for any diagnosis of parkinsonism 1, 3
• At least one additional cardinal sign must accompany bradykinesia: resting tremor, rigidity, or postural instability (though postural instability typically appears later in disease progression) 1, 4
• Bradykinesia affects fine motor tasks (buttoning clothes, writing), gross motor activities (walking, turning), facial expressions, and speech 1

Systematic Physical Examination Approach

For assessing rigidity:

• Passively move the patient's limbs while instructing complete relaxation 1
• Test both upper and lower extremities through full range of motion at varying speeds, comparing sides for asymmetry 1, 2
• Note constant resistance throughout movement (lead-pipe rigidity) or ratchet-like jerky resistance (cogwheel phenomenon when combined with tremor) 1
• Use activation maneuvers - have the patient open/close the opposite hand while testing for rigidity, as this enhances detection of subtle rigidity that might otherwise be missed 1, 2

Common pitfall to avoid: Failure to have the patient completely relax during testing leads to false positives from voluntary muscle contraction 1

Diagnostic Imaging Algorithm

When to Use Imaging

• Imaging is indicated when clinical presentation is unclear or diagnosis is uncertain 1, 5
• Motor symptoms typically appear only after 40-50% of dopaminergic neurons in the substantia nigra have been lost, making early clinical diagnosis challenging 1, 5

First-Line Imaging Modality

• I-123 ioflupane SPECT/CT (DaTscan) is the definitive test for differentiating parkinsonian syndromes from essential tremor and drug-induced tremor 2, 5
• Shows decreased radiotracer uptake in the striatum (usually beginning in putamen, progressing to caudate) in parkinsonian syndromes 1
• A normal DaTscan essentially excludes all parkinsonian syndromes - this is critical for ruling out the diagnosis 1, 2, 5
• Demonstrates abnormality early in disease course compared with anatomic imaging like CT or MRI 5

Alternative Imaging Options

• MRI brain without contrast is optimal when structural causes need exclusion, though often normal in early PD 1, 5
• MRI provides superior soft-tissue characterization and sensitivity to iron deposition compared to CT 5
• FDG-PET/CT brain is useful for discriminating progressive supranuclear palsy (PSP) from idiopathic PD based on metabolic patterns 5
• CT has limited utility due to poor soft tissue contrast but can help exclude structural lesions or vascular disease 1

Critical Differential Diagnosis Considerations

Red Flags Suggesting Atypical Parkinsonism (Not Idiopathic PD)

• Vertical gaze palsy, especially downward → suggests Progressive Supranuclear Palsy 1, 2
• Asymmetric rigidity with alien hand phenomenon → suggests Corticobasal Syndrome 1, 2
• Ataxia → suggests alternative diagnosis 1
• Early occurrence of gait difficulty, postural instability, dementia, or hallucinations 6
• Dysautonomia, ophthalmoparesis, or poor/no response to levodopa 6

Must Exclude Drug-Induced Parkinsonism

• Obtain thorough medication history, particularly for antipsychotics and antiemetics 2
• Drug-induced parkinsonism must be distinguished from other parkinsonian syndromes 1, 2
• DaTscan can differentiate drug-induced tremor (normal scan) from true parkinsonian syndromes (abnormal scan) 2

Assessment Tools for Disease Severity

• Unified Parkinson's Disease Rating Scale (UPDRS) is the standard clinical assessment tool 1, 7
• Consists of four parts: mentation (Part I), activities of daily living (Part II, scored 0-52), motor examination (Part III, scored 0-108), and complications of therapy (Part IV) 1, 7
• Movement Disorder Society-UPDRS (MDS-UPDRS) is a newer version with improved evaluation of non-motor aspects, freezing of gait, and tremor subtypes 1

Ongoing Monitoring Requirements

• Regular monitoring of nutritional and functional status throughout disease course is essential 1
• Monitor body weight changes, vitamin status, dysphagia screening, and nutritional risk assessment, as 15% of community-dwelling PD patients are malnourished 1