Distinctive Pathophysiology Underlying Constipation in Parkinson's Disease: Implications for Cognitive Inefficiency

Depression is associated with constipation within and outside Parkinson's disease (PD). Since inefficient cognitive-processing (bradyphrenia) features in PD and an enterokinetic agent improved cognitive performance in healthy individuals, bradyphrenia may be associated with constipation. We aim to define the archetypical bowel function of PD, and its association with cognition, mood, and motor features within and outside PD. We assessed colonic transit time (oral radio-opaque markers over 6 days), bowel function and psychometric questionnaires and measures of PD facets, including bradyphrenia, in 58 participants with diagnosed PD, and 71 without (controls). The best abdominal X-ray (day 7) predictors of PD status were total retained marker count and transverse colon segmental delay. However, Rome functional constipation status complemented segmental delay better, giving good specificity (85%) but low sensitivity (56%). Transverse colon marker count appeared to be age-associated only in PD. In PD, those correctly classified by bowel dysfunction had higher depression scores (p = 0.02) and longer cognitive-processing times than the misclassified (p = 0.05). Controls misclassified as PD by bowel dysfunction had higher depression and anxiety scores than the correctly classified (p = 0.002 and 0.003, respectively), but not slower cognitive processing. Measures of motor features were independent of sub-classification by bowel function in PD and in controls. In conclusion, constipation in PD has distinct localized pathophysiology, and is associated with bradyphrenia.