This study aim to evaluate the correlation between Quality of Life (QoL) and severity of Parkinson's Disease (PD) by assessing the presence of an optimal cut-off point on the Parkinson's disease questionnaire (PDQ-39) as related to the Hoehn & Yahr (H&Y) scale in a cohort of Italian adults with PD.

A multicenter, cross-sectional study was performed in central and northern Italy. This study was conducted on a cohort of consecutive individuals at three neurologic outpatient clinics. All participants were evaluated with the PDQ-39, and the severity of PD was recorded according to the H&Y scale by a neurologist. Receiver operating characteristic (ROC) curves and coordinates of the curve, which were visually inspected, were used to find cut-off points with optimal sensitivity and specificity. These were in turn used to determine the optimal PDQ-39 cut-off score for identifying disease severity according to H&Y stages.

Inclusion Criteria:

• age > 50 but < 90 years,
• H&Y stages I, II, III, and IV,
• a mini-mental state examination > 22 points,
• a minimum level of five years of education.

Exclusion Criteria:

• Individuals with emotional or psychiatric problems (as determined by clinical screening)

Fivehundred thirteen individuals with Parkinson's Disease (PD) were recruited, all of whom agreed to participate and were thus included in the study. From the general analysis resulted that the greatest number of participants were stage II, according to Hoehn & Yahr (H&Y), followed by stage III, stage I, and finally stage IV. Participants between the age of 50 and 69 were mainly stage I or II, while participants aged 70 to 89 had a greater severity of PD (stage II and III). Most women were in H&Y stage II and III, while most men were mainly in stage II, followed by stage I and III, with a very similar number of participants. A common result for all analyses was the presence of a very low number of participants with stage IV.