Improving diagnostic accuracy of PSP-P

PSP folks –

This article was written by two heroes of the PSP community — David Williams, who is now in Australia, and Andrew Lees, in the UK.

“The aim of this study was to identify particular clinical features (green flags) that may be helpful in differentiating PSP-P from…other disorders.”  PSP-P, the parkinsonism form of PSP (progressive supranuclear palsy), is easily confused with Parkinson’s Disease (PD), multiple system atrophy (MSA), and vascular parkinsonism.  The issue is that the PSP diagnostic criteria include symptoms that are specific to the dementia form of PSP.  But what if someone with PSP-P comes along?

In this study, researchers compared many Queen Square Brain Bank cases:  37 patients with PSP-P, 444 with PD, 46 with dementia with Lewy bodies (DLB), 90 with MSA, and 19 with vascular parkinsonism.

By the way, a total of 127 PSP brains from QSBB were examined.  Of those, 86 had Richardson’s Disease, or the dementia form of PSP, while 37 had PSP-P.  (Four cases must’ve had rare forms of PSP.)  The researchers describe this division as follows:

“PSP cases were further divided according to their clinical features present in the first 2 years of disease. When the clinical notes recorded falls, supranuclear gaze palsy, abnormal vertical saccadic eye movements or cognitive decline within the first 2 years patients they were classified as RD (n = 86). Patients were classified PSP-P when their history included asymmetric bradykinesia, rigidity, a positive L-dopa response or tremor, and the cardinal features of RD were not present (n = 37).”

That breakdown — 29% with PSP-P and 68% with RD — is roughly what we see in our local support group:  most have the dementia form of PSP but about a third have the parkinsonism form.

The authors state:  “The clinical differences between RD and PSP-P are most likely to be due to differences in pathological severity.”  (By the way, an effort is apparently on to rename the dementia form of PSP to “Richardson’s Disease,” or RD, rather than Richardson’s Syndrome.)

Past studies have shown that the diagnostic accuracy for RD is much higher than that for PSP-P: 86% vs. 41%.

After comparing the clinical records, researchers found no clinical features “predictive” of PSP-P.  (No wonder this form of PSP is so hard to diagnose!)

In distinguishing PD, DLB, and PSP-P, three clinical features were found to be most important:  “late drug induced dyskinesias, late autonomic dysfunction, and any visual hallucinations.”  These three symptoms are very uncommon in PSP and “may be helpful exclusion criteria.”  Note that none of these three features is an early symptom.

Researchers also found many features to distinguish MSA and PSP-P:

“Late non-specific eye symptoms and supranuclear gaze palsy were good discriminators of PSP-P. Three other clinical features, when calculated with respect to a diagnosis of MSA, appeared to be reasonable discriminators of MSA, including early autonomic dysfunction, late autonomic dysfunction, and late cerebellar signs, which occurred in more than 50% of MSA patients and less than 10% of PSP-P patients.”

These statements in the Discussion section about differentiating PSP from PD were interesting:

“The nature of bradykinesia has rarely been examined in detail in different diseases, but our impression is that rapid hypokinesia – reduced amplitude of movement, that is, fast and without decay, is more typical in patients with PSP than true bradykinesia typical of PD. Equally, fast micrographia and rapid hypophonia may also be clues to PSP pathology.”

This may be enough for most of you.  The abstract follows.

Robin

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Movement Disorders. 2010 Jan 27. [Epub ahead of print]

What features improve the accuracy of the clinical diagnosis of progressive supranuclear palsy-parkinsonism (PSP-P)?

Williams DR, Lees AJ.
Van Cleef Roet Centre for Nervous Diseases, Monash University, Melbourne, Victoria, Australia.

Progressive supranuclear palsy-parkinsonism (PSP-P) is a primary tauopathy characterised by neurofibrillary degeneration, which is frequently mistaken for Parkinson’s disease (PD), multiple system atrophy (MSA), and vascular parkinsonism (VP) at presentation. The aim of this study was to identify particular clinical features (green flags) that may be helpful in differentiating PSP-P from these other disorders.

We identified 37 patients with PSP-P from 726 patients archived at the Queen Square Brain Bank. Using a retrospective case notes review the clinical features were compared between the PSP-P group and Lewy body associated parkinsonism (PD, n = 444 and dementia with Lewy bodies (DLB), n = 46), MSA (n = 90), and VP (n = 19), using the chi(2)-test for proportions for a two-by-two contingency table.

The sensitivity, specificity, and positive predictive values (PPV) and negative predictive values (NPV) were calculated for individual clinical features. A specificity of >0.85 or a PPV of >0.85 were considered reliable discriminators.

No clinical features were predictive of PSP-P, but late drug induced dyskinesias (specificity 0.92, PPV 0.99), late autonomic dysfunction (specificity 0.94, PPV 0.99) and any visual hallucinations (specificity 0.94, PPV 0.99) were better in distinguishing PD and PSP-P than predicted using operational diagnostic criteria for PD. PSP-P shares many clinical features with PD and DLB, MSA and VP, but visual hallucinations, drug induced dyskinesias and autonomic dysfunction are very uncommon and may be helpful exclusion criteria.

PubMed ID#: 20108379   (see pubmed.gov for this abstact only – available at no charge)