Objective: Aims of the present study were

• to confirm hypodipsia as a characteristic feature of PSP and

• to offer hypothesis on the pathological substrate for hypodipsia in PSP patients.

Background: Progressive supranuclear palsy (PSP) may be difficult to distinguish from other Parkinsonian syndromes, particularly from Parkinson’s disease (PD). However, these syndromes differ both in their prognosis as well as in their therapy. A previous study proposed hypodipsia (reduced thirst) as a useful parameter to discriminate between PSP and PD [Stamelou et al., 2011].

Methods: In patients with a probable clinical diagnosis of PSP (N=8), and PD (N=9), and in healthy controls (HC, N=11), we provoked thirst with a 3% NaCl-infusion at a rate of 11.4 ml/kg body weight/hour for 50 min. The level of thirst was assessed with a standardized thirst questionnaire scaled from 0 to 8 (0=no thirst, 8=maximal thirst) every 5 minutes. At the end of the study, the volume of water each subject drank until satiation was recorded. Serum-osmolality and ADH levels were assessed before and after the infusion period. A functional brain imaging paradigm was carried out in a 3T-MRI scanner, during which the subjects looked at ten consecutive blocks of either thirst stimulating images (e.g. drinking people) or neutral images (e.g. empty streets, plants). To assess the level of thirst these images provoked, subjects were asked to press one of eight buttons (1= no thirst, 8=maximal thirst) after each activation block. A resting-state MRI (rsMRI) for network analysis before and after NaCl-infusion was also performed.

Results: PSP patients reported less thirst than PD patients and HC (2-way ANOVA, P<0.001). After the test, PSP patients drank significantly less water to satiation than PD patients and HC (ANOVA, P<0.05). No significant differences in ADH levels and serum osmolality among PSP, PD, and HC were found. Several brain areas were significantly less activated in PSP and PD patients compared to HC, particularly the left putamen and the precuneus bilaterally. Analyses of rsMRI are underway.

Conclusions: Based on the fMRI findings, we propose that the expectation- and the reward-system associated with the putamen and the precuneus may be impaired in both, PSP and PD. Analysis of changes in pre- and post-infusion rsMRI will provide further insights into changes associated with hypodipsia in PSP.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/imaging-correlates-of-hypodipsia-in-progressive-supranuclear-palsy/