Validation of the "QUICK" questionnaire--a tool for diagnosis of "wearing-off" in patients with Parkinson's disease.

The main objective of the present study was to test the validity of a 19-items instrument (QUICK Questionnaire, QQ) as a tool for screening of WO. Two hundred twenty-two patients (36.0% without WO; 64.0% with mild or moderate/severe WO) were included. Diagnosis of WO by the participant neurologist was considered the "gold standard." The complete Unified Parkinson's Disease Rating Scale battery, the Cumulative Illness Rating Scale-Geriatrics, and a form about WO presence and severity were completed by the neurologist. Patients independently completed the QQ just before the clinical assessment. As a whole, patients with WO were more disabled than patients without and patients with moderate/severe WO were in worse condition than patients with mild WO. The number of QQ symptoms declared to improve usually after the following dose of medication was 1.0 +/- 1.8 in the group without WO, but 6.0 +/- 3.8 in patients with WO (P < 0.001). A two QQ positive symptoms cut-off showed the following attributes: sensitivity, 88%; specificity, 80%; positive predictive value, 88.7%; negative predictive value, 79%; diagnostic accuracy, 85%; positive and negative likelihood ratios 4.4 and 0.15, respectively. The area under the ROC curve resulted 0.90 (CI95%: 0.86-0.94%). In summary, the QQ proved to be a valid screening tool to identify WO in PD patients. To our knowledge, the QQ is the only validated tool for diagnosis of WO.