What is the recommended initial clinical assessment and diagnostic testing for a patient with suspected Parkinson disease?

How to Test for Suspected Parkinson's Disease

The diagnosis of Parkinson's disease is primarily clinical, based on identifying bradykinesia plus either resting tremor or rigidity, with neurologist confirmation required; when the clinical picture is unclear, obtain MRI brain first to exclude structural causes, followed by I-123 ioflupane SPECT/CT (DaTscan) to differentiate true Parkinsonian syndromes from mimics like essential tremor or drug-induced parkinsonism. 1

Initial Clinical Assessment

Essential Motor Features to Document

• Bradykinesia is mandatory - this slowness of movement must be present for diagnosis and affects fine motor tasks (buttoning clothes, writing), gross motor activities (walking, turning), facial expressions, and speech. 1

• Plus at least one of the following cardinal signs:

  • Resting tremor - typically 4-6 Hz, present at rest and diminishing with action 1, 2
  • Rigidity - assess by passively moving the patient's limbs while instructing complete relaxation, testing both upper and lower extremities through full range of motion at varying speeds 1
  • Postural instability - though this typically appears later in disease progression 1

Technique for Detecting Rigidity

• Have the patient relax completely while you passively move their limbs through full range of motion 1
• Compare sides for asymmetry, as PD typically presents asymmetrically 1
• Note constant resistance throughout movement (lead-pipe rigidity) or ratchet-like jerky resistance when combined with tremor (cogwheel phenomenon) 1
• Use activation maneuvers - ask the patient to open and close the opposite hand while testing for rigidity, as this often brings out subtle rigidity that might otherwise be missed 1, 3

Red Flags Suggesting Alternative Diagnoses

• Early severe autonomic dysfunction, cerebellar signs, or pyramidal signs suggest Multiple System Atrophy rather than PD 1
• Vertical gaze palsy, especially downward indicates Progressive Supranuclear Palsy 1
• Asymmetric rigidity with alien hand phenomenon points to Corticobasal Syndrome 1
• Ataxia suggests an alternative parkinsonian syndrome 1

Diagnostic Testing Algorithm

Step 1: Exclude Secondary Causes

• Medication history - rule out drug-induced parkinsonism from antipsychotics, antiemetics, or other dopamine-blocking agents 1, 3
• For patients under 50 years old, exclude Wilson's disease by measuring serum ceruloplasmin, 24-hour urinary copper excretion, and performing slit-lamp examination for Kayser-Fleischer rings 1
• Thyroid function tests (TSH, free T4) to exclude hyperthyroidism 1
• Metabolic screening including blood glucose, calcium-phosphorus metabolism, and serum bilirubin 1

Step 2: Structural Imaging

• MRI brain without contrast is mandatory as the first imaging study - this is the optimal modality due to superior soft-tissue characterization and sensitivity to iron deposition 1, 4
• MRI rules out structural lesions, vascular disease, hydrocephalus, or focal abnormalities that could explain parkinsonism 1
• Common pitfall: Never skip structural imaging before ordering functional imaging; structural causes must be excluded first 1
• MRI is often normal in early PD, which is expected and does not exclude the diagnosis 1

Step 3: Functional Imaging (When Diagnosis Remains Uncertain)

• I-123 ioflupane SPECT/CT (DaTscan) is the definitive test when clinical diagnosis is uncertain after history, examination, and MRI 1, 3, 4

• How DaTscan works: The radiotracer binds to presynaptic dopamine transporters in the striatum, visualizing dopaminergic neuronal loss 1

• Interpretation:

  • Abnormal scan (decreased striatal uptake, typically progressing from posterior putamen to anterior caudate) confirms dopamine-deficient parkinsonian syndrome 1, 4
  • Normal scan essentially excludes Parkinsonian syndromes and supports diagnoses of essential tremor, drug-induced tremor, or psychogenic parkinsonism 1, 3, 4

• Key limitation: DaTscan cannot differentiate among specific Parkinsonian syndromes (PD vs. MSA vs. PSP vs. CBD) - all show abnormal dopaminergic depletion 1

Step 4: Additional Imaging for Atypical Features

• FDG-PET/CT can help differentiate Progressive Supranuclear Palsy from idiopathic PD by showing characteristic hypometabolism in medial frontal and anterior cingulate cortices, striatum, and midbrain 1, 4
• Do not order amyloid PET/CT or tau PET/CT - there is no evidence supporting their use in evaluating parkinsonian syndromes 1

Specialist Referral

• General neurologists or movement disorder specialists must confirm the diagnosis because correctly diagnosing a parkinsonian syndrome on clinical features alone is challenging 1
• Specialist involvement is critical to avoid missing atypical parkinsonian syndromes (PSP, MSA, CBD) that have different prognoses and treatment responses 1
• Imaging studies require proper interpretation in clinical context, another reason for neurologist involvement 1

Assessment Tools for Disease Severity

• Unified Parkinson's Disease Rating Scale (UPDRS) is the standard clinical assessment tool, consisting of four parts: mentation, activities of daily living, motor examination, and complications of therapy 1, 5
• The Movement Disorder Society-UPDRS (MDS-UPDRS) is a newer version with improved evaluation of non-motor aspects, freezing of gait, and tremor subtypes 1

Common Diagnostic Pitfalls to Avoid

• Failure to have the patient completely relax during rigidity testing leads to false positives from voluntary muscle contraction 1
• Not using activation maneuvers may cause you to miss subtle rigidity 1, 3
• Confusing spasticity with rigidity - spasticity is velocity-dependent (increases with faster stretching) while rigidity shows constant resistance throughout movement 1
• Ordering functional imaging before structural imaging - always obtain MRI first 1
• Assuming a normal MRI excludes PD - MRI is often normal in early PD but is essential to exclude alternative diagnoses 1