Objective: To describe changes in cerebral glucose metabolism in patients with different described clinical phenotypes of PSP and to correlate them with the clinical manifestations of the disease.

Background: Clinicopathological studies have led to the recognition of different clinical phenotypes associated with PSP-tau pathology. The most common PSP subtypes are  the classic Richardson’s syndrome and parkinsonian-PSP. Brain metabolism on fluorodeoxyglucose (FDG)-positron emission tomography (PET) has been identified as a potential biomarker to differentiate PSP from other diseases. 

Methods: We performed a retrospective selection of 15 patients diagnosed with PSP who had a brain metabolism study using PET-fluorodeoxyglucose (FDG). Clinically, patients were classified as PSP type Richardson syndrome (RS-PSP, 9 patients) and parkinsonian-PSP (P-PSP, 6 patients). 
We proceeded to an image analysis based on voxels using the SPMS program with respect to a control group (n=20). PET-FDG images were normalized by reference to the brainstem. A correction of p <0.0001 with 100 voxels was used.

Results: The brain metabolism pattern of the RS-PSP group with respect to the control group showed a hypometabolism of the caudate, thalamic and midbrain nuclei. The pattern of the P-PSP group with respect to the control group was characterized by hypometabolism of the cingular cortex, caudates and both thalamIc nuclei. Our results indicate that FDG-PET scan might be a useful tool to differentiate PSP subtypes.

Conclusions: In the RS-PSP a thalamic and midbrain involvement is predominant. The P-PSP shows a predominant affectation of the caudate nuclei and the thalamus.The mesencephalic affectation objectified in the RS-PSP group, unlike the PSP-P group, correlates with the paralysis of the characteristic vertical gaze of the first type. These functional neuroimaging findings coincide with the clinical expression of these PSP phenotype subtypes and would help to better identify patients with PSP. 

References: Williams DR, de Silva R, Pavior DC, Pittman A, Watt HC, Kliford L, Holton JL, Revesz, Lees AJ. Characterisitcs of two distinct clinical phenotypes in pathologically proven progressive supranueclear palsy: Richardson´s syndrome and PSP- parkinsonism. Brain 2005 Jun;128(Pt 6):1247-58.

Srulijes K, Reimold M, Liscic RM, Bauer S, Dietzel E, Liepelt-Scarfone I, Berq D, Maetzler W. Fluorodeoxyglucose Positron Emission Tomography in Richardson´s Syndrome and Progressive Supranuclear Palsy-Parkinsonism. Mov Disord. 2012 Jan;27(1):151-5.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/brain-metabolic-patterns-in-progressive-supranuclear-palsy-phenotypes/