## 4 Discussion  
The longitudinal observation of a cohort of patients with PD from 2018 to 2021 allowed us to have a comprehensive view of what happened in recent years. 2020 was the most critical year because we were taken aback by the spreading of the COVID-19 pandemic and suffered the strictest and most challenging lockdown measures. 2021 combined the long-term response to the pandemic with the resumption of follow-up visits and face-to-face rehabilitation sessions, the implementation of remote technology solutions, and, eventually, the introduction of the most important prevention tool, i.e., the vaccines against the SARS-CoV-2 virus. Data from 2018 and 2019 presented the health status of patients with PD immediately before the pandemic and offered a reference point for the interpretation of disability progression across the whole period of interest. The current understanding of evolving disability in PD shows some limitations linked to the limited number of studies, [21; 22; 23; 24; 25; 26; 27; 28], the frequent cross-sectional designs that overestimate the actual rate of progression, [21] and/or different and limited measures of disability. However, authors largely agree that the growth curve, or change over time, for MDS-UPDRS is curvilinear [21; 28] and that there is little to no change in motor and functional status through 12 months [21; 27] [PERSON] et al. [21] showed that the adjusted linear effect at 18 months is 1.79 (95% CI 0.99, 2.59) and at 24 months is 2.48 (95% CI 1.16, 3.79), a 2.5 point increase at 2 years. [PERSON] et al. [29] showed that the mean deterioration of motor and disability scores ranges from 2.4 to 7.4% of the maximum possible score per year, and standard deviations indicated the considerable variability of progression rates between individuals. The progression of motor scores decreases with follow-up over 4 years and significantly declines in more advanced disease stages. The deterioration of disability scores does not differ between disease stages; this may reflect the increasing rate of non-motor symptoms or disease complications, which contribute to increasing disability in addition to motor impairment alone in more advanced disease. [PERSON] et al. [23] found a mean annual decline in the UPDRS motor score of 3.2%, and the UPDRS Activity of Daily Living (ADL) score changed similarly, by 3.6% per year. Many authors demontrated that age, age at onset, disease duration, mild cognitive impairment at baseline, severe rigidity or bradykinesia, prominent gait problem at the onset, and nonmotor symptoms (i.e., rapid eye movement, sleep behavior disorder, mild cognitive impairment and orthostatic hypotension) are strong and independent predictors of greater impairment and rapid evolution in motor function and disability [23; 30]  
Our sample, followed retrospectively for 4 years, lies outside the range of progression identified in the literature, which characterizes the motor and functional evolution of individuals with PD. In particular, the mean progression in UPDRS II and III scores over the 2019-2020 period identifies a singular anomaly. In contrast, the evolution describedin the previous period (i.e., 2018-2019) followed the reference pattern, while that of the 2020-2021 biennium tends to go back toward expected values. The standard deviations are large in relation to the variability of the enrolled sample. However, the median shows that the motor, non-motor, and functional evolution described in our study does not relate to a normal evolution of PD history but seems to be influenced by external and novel factors. In the literature, many studies focused on the self-perceived health status change reported by patients with PD during and after the outbreak of COVID-19 [31; 32; 33]. In this study, we used objective clinical and functional measures to establish the impact of restricted access to personalized care and the limitations to physical activity imposed by the lockdown on the health status of a cohort of PD patients referred to a Movement Disorder Center for regular monitoring.