The Parkinson's disease symptom inventory (PDSI): a comprehensive and sensitive instrument to measure disease symptoms and treatment side-effects.

Parkinson's disease (PD) is associated with an array of signs and symptoms and motor fluctuations. In addition, treatments such as levodopa and dopamine agonists are associated with side-effects that impact the same health domains as disease symptomatology. To comprehensively and sensitively assess drug therapies in respect of disease symptoms and side-effects, we designed the Parkinson's disease symptom inventory (PDSI). The PDSI consists of 51 symptoms items identified through expert opinion, patient interviews, and the medical literature. Items represent a detailed array of motor, postural, muscular, gastro-intestinal, emotional, and cognitive domains. Subjects are asked to report the frequency with which each symptom is experienced, as well as the associated subjective distress. After initial elimination of 8 items that did not meet retention criteria, psychometric analysis showed excellent internal consistency (alpha=0.92-0.95) and acceptable reproducibility (ICC=0.72-0.79) of items. Comparison of results with the Unified Parkinson's disease rating scale (UPDRS) and the Parkinson's impact scale (PIMS) revealed correlation with the PDSI, with Pearson's r values of roughly 0.5 and 0.7, respectively. The PDSI demonstrated power to discriminate mean scores of patients comprising the highest and lowest tertiles of the UPDRS and PIMS instruments. In summary, the PDSI demonstrated good psychometric performance characteristics, and may yield valuable data regarding the comparative effectiveness of PD therapies.