Journal of Neurology

, Volume 255, Issue 2, pp 255-264

First online:

Cognitive impairment in 873 patients with idiopathic Parkinson's disease

Results from the German Study on Epidemiology of Parkinson's Disease with Dementia (GEPAD)
  • O. RiedelAffiliated withInstitute of Clinical Psychology and Psychotherapy, Technical University of Dresden
  • , J. KlotscheAffiliated withInstitute of Clinical Psychology and Psychotherapy, Technical University of Dresden
  • , A. SpottkeAffiliated withDept. of Neurology, Friedrich-Wilhelms-University Bonn
  • , G. DeuschlAffiliated withDept. of Neurology, Christian-Albrechts-University Kiel
  • , H. FörstlAffiliated withDept. of Psychiatry and Psychotherapy, Technical University of Munich
  • , F. HennAffiliated withBrookhaven National Laboratory
  • , I. HeuserAffiliated withCharite-Campus-Benjamin Franklin, Universitatsmedizin
  • , W. OertelAffiliated withDept. of Neurology, Philipps-University Marburg
  • , H. ReichmannAffiliated withDept. of Neurology, Faculty of Medicine Carl Gustav Carus
    • , P. RiedererAffiliated withDept. of Clinical Neurochemistry, Clinical Neurochemistry and NPF-Center of Excellence Laboratories University
    • , C. TrenkwalderAffiliated withInstitute of Clinical Psychology and Psychotherapy, Technical University of DresdenParacelsus-Elena-Clinic
    • , R. DodelAffiliated withDept. of Neurology, Philipps-University Marburg
    • , H.-U. WittchenAffiliated withInstitute of Clinical Psychology and Psychotherapy, Technical University of Dresden Email author 

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Parkinson's disease (PD) is often accompanied by non-motor complications, such as dementia, depression, and psychotic symptoms, which worsen the prognosis and increase the personal and socioeconomic burden of disease. Prevalence estimates of these complications are quite variable and are lacking for the outpatient care sector.


As part of a larger, nationwide, cross-sectional epidemiological study in n = 315 neurological outpatient settings in Germany, this paper estimates the frequency of dementia and cognitive impairment in n = 873 outpatients meeting the UK Brain Bank criteria for idiopathic PD. Assessments were based on a clinical interview and neuropsychological assessments, including the Hoehn & Yahr rating and Unified Parkinson's Disease Rating Scale (UPDRS). Cognitive impairment was assessed by the Mini-Mental State Exam (MMSE), Clock Drawing Test (CDT) and the Parkinson Neuropsychometric Dementia Assessment (PANDA) and the clinician's diagnosis of dementia was based on the diagnostic criteria of DSMIV.


Using standardized cutoff scores, the prevalence of cognitive impairment in the study sample as measured by various methods was 17.5% by MMSE (≤ 24), 41.8% by CDT (≥ 3), 43.6% by PANDA (≤ 14), and 28.6% met the DSM-IV criteria for dementia. All estimates increased with age and PD severity. Gender was an inconsistent contributor while illness duration had no significant impact on cognition. Multiple regression analyses revealed PD severity to be the strongest predictor of dementia risk (OR = 4.3; 95% CI: 2.1–9.1), while neuropsychiatric syndromes had independent, although modest additional contributions (OR = 2.5, 95% CI: 1.6–3.8).


Estimates of cognitive impairment and dementia in PD patients are largely dependent on the diagnostic measure used. Using established clinical diagnostic standards for dementia the overall rate on routine outpatient neurological care is 28.6%, but using more sensitive neuropsychological measures, rates for cognitive impairment might be up to 2-fold higher. The MMSE revealed strikingly low sensitivity. Neuropsychiatric syndromes, in addition to PD severity and age, have an independent – although modest – additional contribution to patients' risk for cognitive impairment and dementia.

Key words

Parkinson's disease dementia cognitive impairment MMSE CDT PANDA