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The AMC Linear Disability Score in patients with newly diagnosed Parkinson disease

From the Departments of Neurology (N.W., B.P., J.D.S., M.V.) and Clinical Epidemiology and Biostatistics (R.J.d.H.), Academic Medical Center, University of Amsterdam; and Department of Educational Measurement (C.A.W.G.), University of Twente, Enschede, the Netherlands.

Address correspondence and reprint requests to Dr. Nadine Weisscher, Department of Neurology, H2-236 Academic Medical Center, 1105 AZ Amsterdam, The Netherlands n.weisscher{at}amc.uva.nl

Objective: The aim of this study was to examine the clinimetric properties of the AMC Linear Disability Score (ALDS), a new generic disability measure based on Item Response Theory, in patients with newly diagnosed Parkinson disease (PD).

Methods: A sample of 132 patients with PD was evaluated using the Hoehn and Yahr (H&Y), the Unified PD Rating Scale motor examination, the Schwab and England scale (S&E), the Short Form–36, the PD Quality of Life Questionnaire, and the ALDS.

Results: The internal consistency reliability of the ALDS was good ( = 0.95) with 55 items extending the sufficient item-total correlation criterion (r > 0.20). The ALDS was correlated with other disability measures (r = 0.50 to 0.63) and decreasingly associated with measures reflecting impairments (r = 0.36 to 0.37) and mental health (r = 0.23 to –0.01). With regard to know-group validity, the ALDS indicated that patients with more severe PD (H&Y stage 3) were more disabled than patients with mild (H&Y stage 1) or moderate PD (H&Y stage 2) (p < 0.0001). The ALDS discriminated between more or less severe extrapyramidal symptoms (p = 0.001) and patients with postural instability showed lower ALDS scores compared to patients without postural instability (p = < 0.0001). Compared to the S&E (score 100% = 19%), the ALDS showed less of a ceiling effect (5%).

Conclusion: The AMC Linear Disability Score is a flexible, feasible, and clinimetrically promising instrument to assess the level of disability in patients with newly diagnosed Parkinson disease.

Abbreviations: ADL = activities of daily living; ALDS = AMC Linear Disability Score; ANOVA = analysis of variance; H&Y = Hoehn and Yahr; IRT = item response theory; PD = Parkinson disease; PDQL = PD Quality of Life Questionnaire; S&E = Schwab and England scale; SF = Short Form; UPDRS = Unified PD Rating Scale.

Supplemental data at www.neurology.org

The CARPA study group is supported by a grant from ZonMw, The Hague, the Netherlands. N. Weisscher is supported by a grant from the Anton Meelmeijer Fonds, a charity supporting innovative research in the Academic Medical Center, Amsterdam, the Netherlands.

Disclosure: The authors report no conflicts of interest.

Received January 31, 2007. Accepted in final form May 30, 2007.

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