Alexithymia and anhedonia in early Richardson's syndrome and progressive supranuclear palsy with predominant parkinsonism

Introduction: Phenotypic variants of progressive supranuclear palsy (PSP) are all characterized by the combination of motor symptoms of parkinsonism with a number of neuropsychiatric and cognitive disorders. Despite the strong effort in characterizing these features in PSP, alexithymia and anhedonia have not been investigated at present. Here, we aimed at investigating the qualitative and quantitative differences of alexithymia and anhedonia in the two more frequent variants of PSP, Richardson's syndrome (PSP-RS) and PSP with predominant parkinsonism (PSP-P) compared to Parkinson's disease (PD) patients recruited within 24 months after the onset of motor symptoms. Methods: One hundred fifty-five PD, 11 PSP-P, and 14 PSP-RS patients underwent clinical, neuropsychiatric, and neuropsychological evaluations. Alexithymia was assessed using the Toronto Alexithymia Scale-20 item (TAS-20), and hedonic tone was measured by the Snaith–Hamilton Pleasure Scale (SHAPS). Results: In PSP-P and PSP-RS patients, the frequency of alexithymia diagnosis was higher than in PD. On the TAS-20 scores, PSP-RS performed worse in the total score and in F2 sub-scale when compared to PD. Among patients with diagnosis of depression, PSP-RS showed higher scores in TAS-20 total and TAS-20 F2 than PD. No significant differences in TAS-20 scores were found in nondepressed patients. Finally, we did not find significant differences among PD, PSP-P, and PSP-RS groups in the SHAPS scores. Conclusions: Alexithymia is identifiable very early in PSP-P and PSP-RS patients. Alexithymic symptoms differentiate PSP-RS group from PD group but not between the two subtypes of PSP. Further, alexithymia in PSP seems to be predicted by the presence of depression. Altered emotional capability could be related to specific neurophysiological dysfunction occurring precociously in PSP; therefore, its identification could orient the diagnosis toward PSP cases.