The interlocking finger test in patients with Parkinson's disease and healthy subjects

The interlocking finger test (ILFT) is a bedside screening test in which the subject must imitate four bimanual finger gestures without symbolic meaning. We assessed the utility of the test in the cognitive evaluation of patients with Parkinson's disease (PD). We evaluated 88 healthy subjects and 101 patients with PD using a simplified motor score of the Unified Parkinson's Disease Rating Scale (UPDRS), Hoehn and Yahr and Schwab and England scales, Geriatric Depression Scale, Pfeffer Functional Activities Questionnaire, Clinical Dementia Rating, Mini-Mental State Examination, clock drawing test, digit span, word list battery of the Consortium to Establish a Registry for Alzheimer's Disease assessment, Frontal Assessment Battery, semantic verbal fluency test, and the ILFT. Diagnoses of mild cognitive impairment and dementia were made using the Movement Disorder Society diagnostic criteria. ILFT scores in healthy subjects correlated significantly with age (p=0.001) and only one healthy subject scored 2 in the test. ILFT scores were significantly lower in patients with PD and dementia (p=0.001) and significantly correlated with cognitive and functional tests, but not with depressive symptoms (p=0.607), Hoehn and Yahr scores (p=0.907), or Schwab and England scores (p=0.701). Twenty-five patients with dementia, three patients with mild cognitive impairment, and six patients with apparently normal cognition scored less than 3 in the ILFT. The area under the receiver operating characteristic curve for the ILFT to discriminate patients with dementia from those without it was 0.76 (cut-off score of 3/2: sensitivity of 61%, specificity of 0.85). In conclusion, the ILFT seems to be a useful bedside test to assess cognitive impairment in patients with PD.