How is a diagnosis of parkinsonism confirmed?

Confirming a Diagnosis of Parkinsonism

The diagnosis of parkinsonism is primarily clinical, based on the identification of bradykinesia (slowness of movement) plus at least one of the following cardinal signs: resting tremor, rigidity, or postural instability. 1

Clinical Diagnostic Criteria

• Bradykinesia is the essential diagnostic feature for parkinsonism, without which the diagnosis cannot be made 1, 2
• At least one of the following cardinal signs must also be present:
  • Resting tremor (typically 4-6 Hz, most prominent at rest) 1, 3
  • Rigidity (increased resistance to passive movement) 1, 2
  • Postural instability (though this typically appears later in disease progression) 1, 4
• Symptoms typically manifest after approximately 40-50% of dopaminergic neurons in the substantia nigra have been lost 1

Supportive Clinical Features

• Asymmetric onset of symptoms (strongly suggests idiopathic Parkinson's disease) 2, 5
• Specific functional difficulties that support diagnosis:
  • Trouble turning in bed (positive LR 13) 3
  • Difficulty opening jars (positive LR 6.1) 3
  • Problems rising from a chair (positive LR 1.9-5.2) 3
  • Shuffling gait (positive LR 3.3-15) 3
  • Micrographia (small handwriting) (positive LR 2.8-5.9) 3
• Secondary motor symptoms that support diagnosis:
  • Hypomimia (masked facies) 5
  • Dysarthria (speech difficulties) 5
  • Festination (acceleration of gait) 5
  • Freezing episodes 5

Diagnostic Testing

• MRI brain without contrast is recommended when structural causes need to be ruled out, though it is often normal in early parkinsonism 1
• I-123 ioflupane SPECT/CT (DaTscan) is valuable for differentiating Parkinson's disease from conditions that mimic it, such as:
  • Essential tremor 1
  • Drug-induced parkinsonism 1
• A normal DaTscan essentially excludes parkinsonian syndromes 1
• The glabella tap test (positive LR 4.5) can be a useful clinical sign 3

Differential Diagnosis

• Parkinsonism must be differentiated between:
  • Idiopathic Parkinson's disease (most common cause) 4
  • Atypical parkinsonian syndromes:
    • Multiple system atrophy (MSA) 1, 4
    • Progressive supranuclear palsy (PSP) 1, 4
    • Corticobasal degeneration (CBD) 1, 4
    • Dementia with Lewy bodies (DLB) 4
  • Secondary causes (vascular, drug-induced, toxin-induced) 1, 4

Red Flags Suggesting Alternative Diagnoses

• Absence of rest tremor 5
• Early occurrence of gait difficulty and postural instability 5
• Early dementia or hallucinations 5
• Prominent autonomic dysfunction early in disease course 5
• Vertical gaze palsy (especially downward) suggests PSP 6
• Asymmetric rigidity with alien hand phenomenon suggests corticobasal syndrome 6
• Poor or no response to levodopa therapy 5

Pitfalls to Avoid

• Relying solely on tremor for diagnosis, as some forms of parkinsonism may not present with tremor 5
• Failing to differentiate essential tremor (action/postural tremor) from parkinsonian tremor (rest tremor) 1
• Missing drug-induced parkinsonism by not taking a thorough medication history 1
• Overlooking early non-motor symptoms that may precede motor manifestations, such as:
  • Hyposmia (reduced sense of smell) 2, 5
  • REM sleep behavior disorder 2
  • Constipation 2
  • Depression or anxiety 2