What are the diagnostic criteria for Parkinson's disease in older adults?

Parkinson's Disease Diagnostic Criteria

The diagnosis of Parkinson's disease requires bradykinesia (slowness of movement) plus at least one of the following cardinal motor signs: resting tremor or rigidity, with the diagnosis being primarily clinical rather than based on imaging or laboratory tests. 1

Essential Diagnostic Requirements

Bradykinesia is the mandatory core feature that must be present for diagnosis, manifesting as slowness of movement and progressive reduction in speed and amplitude with repetitive actions. 1, 2 This can affect:

• Fine motor tasks (buttoning clothes, writing) 1
• Gross motor activities (walking, turning) 1
• Facial expressions and speech 1

At least one additional cardinal sign must accompany bradykinesia:

• Resting tremor - typically 4-6 Hz, present at rest and diminishing with action 3, 4
• Rigidity - constant resistance throughout passive range of motion (lead-pipe rigidity), or ratchet-like resistance when combined with tremor (cogwheel rigidity) 1, 3

Note that postural instability, while historically listed as a cardinal feature, typically appears later in disease progression (Hoehn and Yahr stage 3) and is not useful for early diagnosis. 2, 5

Clinical Examination Technique

To properly assess rigidity: Passively move the patient's relaxed limbs through their full range of motion at varying speeds, noting any constant resistance. 1 Use activation maneuvers (having the patient open and close the contralateral hand) to enhance detection of subtle rigidity. 1

Key examination findings supporting PD diagnosis:

• Asymmetric symptom presentation (typical for idiopathic PD) 4, 6
• Symptoms typically manifest after 40-50% of substantia nigra dopaminergic neurons are lost 1, 7
• Peak onset age between 60-70 years 7, 2

Red Flags Suggesting Alternative Diagnoses

Immediately refer to a neurologist or movement disorder specialist if any of these features are present, as they suggest atypical parkinsonian syndromes rather than idiopathic PD: 1

• Vertical gaze palsy (especially downward) → Progressive Supranuclear Palsy 1
• Early severe autonomic dysfunction → Multiple System Atrophy 1
• Asymmetric rigidity with alien hand phenomenon → Corticobasal Syndrome 1
• Cerebellar signs or pyramidal signs → Multiple System Atrophy 1
• Ataxia → Alternative diagnosis 1

Role of Diagnostic Imaging

MRI brain without contrast is the optimal initial structural imaging to rule out alternative causes (vascular disease, structural lesions), though it is often normal in early PD. 1

I-123 ioflupane SPECT/CT (DaTscan) is valuable when the clinical presentation is unclear, particularly to differentiate PD from essential tremor or drug-induced tremor. 1 This shows decreased radiotracer uptake in the striatum (beginning in putamen, progressing to caudate). 1 A normal DaTscan essentially excludes parkinsonian syndromes. 1

Specialist Referral

General neurologists or movement disorder specialists should confirm the diagnosis because correctly diagnosing parkinsonian syndromes on clinical features alone is challenging. 1 Common pitfalls without specialist involvement include:

• Missing atypical parkinsonian syndromes (PSP, MSA, CBD) that have different prognoses and treatment responses 1
• Misdiagnosing essential tremor or drug-induced parkinsonism as PD 1
• Failing to recognize mixed pathology in older adults 6

Supporting Clinical Features

Non-motor symptoms that may precede motor symptoms by years (prodromal PD): 6, 5

• Hyposmia (reduced sense of smell) 5
• REM sleep behavior disorder 5
• Constipation 4, 5
• Depression 5

Response to dopaminergic therapy supports the diagnosis: Levodopa or apomorphine testing can help confirm PD when clinical diagnosis is uncertain. 5 Significant improvement with levodopa supports idiopathic PD over atypical parkinsonian syndromes. 3

Common Diagnostic Pitfalls

• Confusing spasticity (velocity-dependent resistance) with rigidity (constant resistance throughout movement) 1
• Diagnosing PD based on tremor alone without bradykinesia 4
• Failing to recognize drug-induced parkinsonism (from antipsychotics, metoclopramide) 1, 6
• Missing vascular parkinsonism in patients with cerebrovascular disease 1
• Not reassessing the diagnosis periodically, as diagnostic accuracy improves with longitudinal follow-up 3, 6