What are the diagnostic criteria for Parkinson's disease?

Diagnostic Criteria for Parkinson's Disease

Parkinson's disease is diagnosed clinically when bradykinesia (slowness of movement) is present along with at least one of the following: resting tremor or rigidity. 1

Essential Diagnostic Feature

• Bradykinesia is the mandatory cardinal sign that must be present for diagnosis 1, 2
• Bradykinesia affects all voluntary movements including fine motor tasks (buttoning clothes, writing), gross motor activities (walking, turning), facial expressions, and speech 1

Additional Required Cardinal Signs (At Least One Must Be Present)

• Resting tremor - typically asymmetric at onset 1
• Rigidity - constant resistance throughout passive range of motion, which may present as lead-pipe rigidity or cogwheel phenomenon when combined with tremor 1

Important Clinical Context

• Postural instability is NOT useful for early diagnosis because it typically appears later in disease progression (Hoehn and Yahr stage 3 or later), usually after 40-50% of dopaminergic neurons in the substantia nigra have been lost 1, 3
• Symptoms typically manifest approximately 5 years after initial neurodegeneration begins 1

Examination Technique for Rigidity Assessment

• 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 1
• Compare sides for asymmetry, as asymmetric presentation is typical 1
• Use activation maneuvers (having the patient open/close the opposite hand) to enhance detection of subtle rigidity that might otherwise be missed 1, 4

Red Flags Suggesting Alternative Diagnoses

• Vertical gaze palsy (especially downward) suggests Progressive Supranuclear Palsy rather than Parkinson's disease 1
• Asymmetric rigidity with alien hand phenomenon suggests Corticobasal Syndrome 1, 4
• Ataxia suggests an alternative parkinsonian syndrome 1
• Early postural instability, poor or absent levodopa response, or rapid progression should raise suspicion for atypical parkinsonism 5

Supportive Diagnostic Tools When Clinical Presentation is Unclear

• I-123 ioflupane SPECT/CT (DaTscan) is the definitive imaging test to differentiate Parkinson's disease from essential tremor or drug-induced tremor 1, 4
• Abnormal DaTscan shows decreased radiotracer uptake in the striatum (beginning in putamen, progressing to caudate) 1
• A normal DaTscan essentially excludes Parkinsonian syndromes and supports diagnoses of essential tremor or drug-induced tremor 1, 4
• MRI brain without contrast is optimal when structural causes need exclusion, though it is often normal in early Parkinson's disease 1

Critical Diagnostic Pitfalls to Avoid

• Drug-induced parkinsonism must be excluded through careful medication history, particularly antipsychotics and antiemetics 4
• Failure to use activation maneuvers during rigidity testing may result in missed subtle rigidity 1
• Confusing spasticity (velocity-dependent resistance) with rigidity (constant resistance throughout movement) 1
• Not having the patient completely relax during examination can produce false positives from voluntary muscle contraction 1

Assessment Tools

• The Unified Parkinson's Disease Rating Scale (UPDRS) or Movement Disorder Society-UPDRS (MDS-UPDRS) is the standard clinical assessment tool for disease severity, evaluating mentation, activities of daily living, motor examination, and complications of therapy 1