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).

[Edit Diagnosis] [Merge dx] [Add prevalence]

Tags: Neurologic Tag this Diagnosis.

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

Pre-Test Probability (Prevalence): %.	Post-Test Probability (Predictive Value): %.	Switch to display mode.
Note that calculating probabilities from more than one** finding is inherently inaccurate because findings are not independent. (For example, using two positive findings that share a common pathogenesis is likely to overestimate the true probability.)

Good Negative Likelihood Ratio
Finding	Result	+LR	-LR
[ + ] Levodopa Responsiveness	+ 0 -	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	+ 0 -	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	Result	+LR	-LR
[ + ] 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

Good Positive and Negative Likelihood Ratios
Finding	Result	+LR	-LR
[ + ] Can Ride a Bicycle	+ 0 -	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	+ 0 -	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	+ 0 -	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	+ 0 -	2	0.5
i.e. 34% of MSA patients have resting tremor. Study: Arch Neurol. 1999 Jan;56(1):33-9. PMID: 9923759