Parkinson's Disease: Likelihood Ratios

Introduction: Specifically, idiopathic Parkinson's. The differential diagnosis would include Essential Tremor, Parkinson's-Plus syndromes (Multi-System Atrophy, Progressive Supranuclear Palsy, Dementia with Lewy Bodies), and secondary Parkinson's (toxic such as MPTP, traumatic such as dementia pugilistica).

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The likelihood ratios of findings for Parkinson's Disease are listed below. See the left navigation bar to change the display.

Good Positive and Negative Likelihood Ratios

Finding	+LR	-LR	Comments, Study
Can Ride a Bicycle	2	0.1	i.e. patient can still ride a bicycle versus Parkinson's-Plus Study: The Lancet 377(9760):125 (2011). http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(11)60018-4/fulltext
Levodopa Challenge	3.7	0.4	250/50 mg of L-dopa-carbidopa for an improvement of 30% on UPDRS score. At 24 month follow-up, they were re-tested with 1 g for 1 month when required. At this point, clinical criteria of the U.K. Parkinson's Disease Society Brain Bank were applied and definitive clinical diagnosis of PD was made. Study: Mov Disord. 2002 Jul;17(4):795-8. PMID: 12210878
Cardinal Features	2.8	0.4	>=2 of tremor, rigidity, and bradykinesia. Confirmed by autopsy. Study: Arch Neurol. 1999 Jan;56(1):33-9. PMID: 9923759
Resting Tremor	2	0.5	i.e. 34% of MSA patients have resting tremor. Study: Arch Neurol. 1999 Jan;56(1):33-9. PMID: 9923759

Good Negative Likelihood Ratio

Levodopa Responsiveness

1.3

0.2

>94% of true PD patients will respond to levodopa in general (see the other entry for a specific study, albeit with lower responsiveness). However, many other disorders, e.g. MSA and DLB, have good initial responsiveness (my 30% was ballparking based on separate series with different diseases).

Study: Arch Neurol. 1999 Jan;56(1):33-9. PMID: 9923759

Asymmetric Onset

1.7

0.5

i.e. 42% of movement disorders that are not PD begin asymmetrically

Study: Arch Neurol. 1999 Jan;56(1):33-9. PMID: 9923759

Poorly Diagnostic Findings

Finding	+LR	-LR	Comments, Study
Rigidity	Sensitivity = 89%		specificity not assessed but believed to be poor Study: Arch Neurol. 1999 Jan;56(1):33-9. PMID: 9923759
Bradykinesia	Sensitivity = 77%		specificity not assessed Study: Arch Neurol. 1999 Jan;56(1):33-9. PMID: 9923759
Postural Instability	Sensitivity = 37%		within first 5 years of presentation. Specificity not assessed, however early postural instability is usually diagnostic of PSP. Study: Arch Neurol. 1999 Jan;56(1):33-9. PMID: 9923759