Pareidolia and Constipation in De Novo Parkinson's Disease: Symptomatic Markers of a Shared Clinical Pattern

Background Pareidolia, defined as the misperception of ambiguous stimuli as meaningful objects, is a frequent visual phenomenon observed in patients with Parkinson's disease (PD). In contrast, constipation is one of the most prevalent non-motor symptoms in PD and appears early in the "body-first" subtype. Pareidolia shares partially overlapping pathophysiological mechanisms with visual hallucinations, which are more frequent in the body-first subtype of PD. The association between pareidolia and constipation, both of which can be observed in the early or prodromal state of PD, has not been previously explored. Therefore, in this study, we aimed to explore the potential relationship between pareidolia and constipation in drug-naïve patients with newly diagnosed PD who did not exhibit obvious hallucinations. Methods Thirty-two consecutive drug-naïve patients with PD admitted to Showa Medical University East Hospital between April 2022 and September 2024 were enrolled. Patients underwent comprehensive neurological and cognitive evaluations, including the Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) Part III, Hoehn and Yahr stage (H-Y), Mini-Mental State Examination (MMSE), and Frontal Assessment Battery (FAB). Constipation was defined based on the Rome IV criteria. Pareidolia was assessed using the Noise Pareidolia Test (NPT). Results Among the 32 patients, 17 (53.1%) were pareidolia-positive and 26 (81.3%) had constipation. Constipation was significantly more common in the pareidolia-positive group than in the pareidolia-negative group (61.5% vs. 16.7%, p = 0.047). Patients with pareidolia were significantly older at disease onset and diagnosis (p = 0.002 and p = 0.004, respectively), had higher H-Y stages (p = 0.049), and lower FAB scores (p = 0.018). The MMSE total scores tended to be lower in the pareidolia-positive group (p = 0.053). However, compared with those without constipation, patients with constipation showed higher H-Y and MDS-UPDRS III scores (p = 0.012 and p = 0.047, respectively), and lower MMSE (p = 0.025) and FAB scores (p = 0.078). Conclusion Patients with pareidolia had more severe motor symptoms and cognitive impairment than those without, and the same pattern was observed when comparing patients with and without constipation. This suggests a potential association between pareidolia and constipation in PD, similar to the relationship between hallucinations and constipation. Our findings indicate that pareidolia and constipation may share a common pathological background, potentially reflecting the body-first subtype of PD.