Hypodipsia discriminates PSP from Parkinson's disease and Multisystem Atrophy

Using a standardized questionnaire, we studied the sensation of thirst in healthy controls (HC; N=13; m:f=6:7; age: 60.3±3.6yrs.) and in early stage (Hoehn & Yahr ≤3) non-demented (MMSE >14), non-depressed (MADRS <18) patients with clinically probable Richardson Syndrome (PSP; N=13; m:f=6:7; age: 62.3±3.8yrs.; H&Y median 2.0), with the Parkinson variant of Multisystem Atrophy (MSA; N=13; m:f=6:7; age: 60.9±4.5yrs.; H&Y median 2.5) or with idiopathic Parkinson's disease (PD; N=13; m:f=7:6; age: 61.3±4.5yrs.; H&Y median 2.5).

69.2% of the PSP patients, but only 0.0% of HC, 7.7% of MSA and 7.7% of PD reported a diminished sensation of thirst (hypodipsia) compared to previous years. Only 23.1% of the PSP patients, but 100.0% of HC, 84.6% of MSA and 76.9% of PD reported that they would still experience an increase in their sensation of thirst as a reaction to hot weather. 84.6% of the PSP patients, but only 15.4% of HC, 30.8% of MSA and 23.1% of PD reported that they would only drink because they knew it was important, but not because they enjoyed drinking. Consequently, 30.8% of the PSP patients, but only 15.4% of HC, 7.7% of MSA and 15.4% of PD reported that they would now drink less than in previous years.

Most PSP patients reported that the sensation of thirst would have changed before (55.6%) or with (22.2%) onset of the motor symptoms. 88.9% reported no progressive worsening of this symptom since onset. They reported no association of the onset of hypodipsia with dysphagia (100%), with functionally relevant impairment of locomotion (84.6%) or with the introduction of new medication (87.5%).

In summary, we report here hypodipsia as a previously unrecognized, nonprogressive symptom in PSP. Since hypodipsia occurs frequently and early in PSP, but is only rarely observed in age-matched HV, PD and MSA, it might prove to be helpful for early differenzial diagnosis of PSP.