A focus on Rome III criteria for the assessment of constipation in Parkinson's disease

We read with great interest the review by Knudsen and colleagues. The authors have tried to summarize in the most comprehensive way the available knowledge on subjective and objective methods to evaluate constipation in Parkinson’s disease (PD). We would like to add some considerations to the discussion on this interesting topic. Constipation could be either a subjective condition or an objective finding of delayed colonic transit, and it would be interesting to detect measurable differences between a subjective and an objective condition. This information would be helpful in the validation (or even the construction) of a reliable PD-specific screening tool or rating scale to be shared by movement disorder specialists. Unfortunately, as reported by Knudsen and colleagues, the criteria for constipation used in literature are heterogeneous, which does not help characterizing this nonmotor symptom. In 2009, the same task force of the Movement Disorder Society, after performing a systematic review of literature on the rating scales used to assess dysautonomic dysfunction in PD, reported that for constipation, no scales or questionnaires met the criteria for suggested or recommended use. Nonetheless, the panel also expressed a positive opinion on the use of Rome III criteria being developed through international consensus and widely accepted in the gastroenterological community. A main advantage is that they address anorectal dysfunction, which we found to be reported by around 75% of patients with constipation. As highlighted by Knudsen and colleagues, a major shortcoming of the use of Rome III criteria in PD is the lack of studies. However, using these criteria, our research group published 4 studies (2 after February 2016), including a randomized trial on the use of prebiotics and probiotics as adjuvant therapy for constipation. In the first 3 studies, we found a prevalence of constipation ranging between 47% to 60% (pooled prevalence, 51%), which is consistent with the pooled estimates provided by the Danish colleagues. We also confirmed the association between increasing prevalence and disease progression (severity/duration). Finally, in our randomized clinical trial, we also provided—for the first time in a PD patient population—an indirect validation of this tool and a focus on the reliability of subjectively reported constipation. In particular, we observed that 120 out of 165 patients (73%) initially self-reporting constipation had the diagnosis confirmed on the basis of the stool diary completed during the 2-week pretreatment phase. Therefore, among PD patients, not only the prevalence of objective colonic dysfunction exceeds the prevalence of subjective constipation but also an overreporting of the symptom does exist. In daily clinical practice, constipation still remains more a subjective condition than an objective finding. However, thinking about a pathophysiologic perspective and the recent interest in the gut–brain axis, objective colonic dysfunction is a more interesting issue and a better characterization is clearly needed not only to have an accurate dimension of the problem but also to clarify its prognostic impact.