Diffusion tensor imaging analysis in three progressive supranuclear palsy variants

Background: Clinical variants of progressive supranuclear palsy (PSP) include the classic Richardson’s syndrome (PSP-RS), as well as cortical presentations such as PSP-speech/language (PSP-SL) and subcortical presentations such as PSP-parkinsonism (PSP-P). Patterns of white matter tract degeneration underlying these variants, and the degree to which white matter patterns could differentiate these variants, is unclear. Methods: Forty-nine PSP patients (28 PSP-RS, 12 PSP-P, and 9 PSP-SL) were recruited by the Neurodegenerative Research Group and underwent diffusion tensor imaging. Regional diffusion tensor imaging metrics were compared across PSP variants using Bayesian linear mixed-effects models, with inter-variant differentiation assessed using the area under the receiver operator characteristic curve (AUROC). Results: All three variants showed degeneration of the body of the corpus callosum, posterior thalamic radiation, superior cerebellar peduncle, internal and external capsule, and superior fronto-occipital fasciculus. PSP-RS showed greater degeneration of superior cerebellar peduncle compared to PSP-P and PSP-SL, whereas PSP-SL showed greater degeneration of body and genu of the corpus callosum, internal capsule, external capsule, and superior longitudinal fasciculus compared to the other variants. Fractional anisotropy in body of the corpus callosum provided excellent differentiation of PSP-SL from both PSP-P and PSP-RS (AUROC = 0.91 and 0.92, respectively). Moderate differentiation of PSP-RS and PSP-P was achieved with fractional anisotropy in superior fronto-occipital fasciculus (AUROC = 0.68) and mean diffusivity in the superior cerebellar peduncle (AUROC = 0.65). Conclusion: In this pilot study, patterns of white matter tract degeneration differed across PSP-RS, PSP-SL, and PSP-P, with the body of the corpus callosum showing some utility in the differentiation of PSP-SL from the other two variants.