The Value of Brain FDG-PET or SPECT in predicting the clinical features of Corticobasal Syndrome

Introduction: Corticobasal Syndrome (CBS) is an atypical parkinsonian syndrome first considered a primarily motor disorder but now recognized as a cognitive disorder associated with several cortical features. The term CBS denotes the phenotype of multiple pathologies, including Corticobasal Degeneration and Alzheimer’s disease (AD). Accurate antemortem diagnosis of underlying pathology in CBS is challenging and new diagnostic methods are being developed to predict the pathology. Propose: To compare the clinical features of patients with probable corticobasal syndrome (CBS) according to different individual brain functional patterns measured with FDG-PET (glucose metabolism) and SPECT (blood flow), exploring the potential role of these imaging techniques as diagnostic biomarkers.

Methods: Sixteen patients with clinical diagnosis of probable CBS underwent to a brain FDG-PET (14 patients) or SPECT with ^99mTc-ECD (2 patients). They were first clinically diagnosed with CBS and investigated in relation to their movement disorders profile and cognitive symptoms. According to the FDG-PET or SPECT patterns, patients were distributed into an AD group (CBS likely related to AD) and a non-AD group (CBS likely unrelated to AD). Both groups were compared in relation to their clinical features and movement disorder profiles. Results: At FDG-PET scan, two patients had an AD pattern and twelve patients presented with a non-AD pattern. At SPECT examinations, one patient had typical AD pattern and the other had non-AD pattern. Clinically, the most prevalent symptoms were akinetic-rigid parkinsonism (100%), limb apraxia (87,5%), myoclonus (56,3%), dystonia (56,3%) and aphasia (50%). Only dystonia demonstrated a significant difference between groups as 100% of individuals with this feature presented a non-AD pattern (p=0,019). Myoclonus showed a tendency to be related to the AD group (p=0,069) and apraxia of speech (31,8%) to the non-AD group, as 100% had a non-AD pattern (p=0,181). There were significant differences between the AD and non-AD groups on Addenbrooke’s Cognitive Examination-Revised (ACE-R) (AD=4,00 + 6,93 vs non-AD=32,50 +- 7,09 p=0,001), Mini Mental Score Examination (MMSE) (AD = 5,25 + 7,54 vs non-AD = 15,02 + 7,24 p = 0,035) and Hoehn and Yahr (HY) scale (AD = 1,75 + 0,86 vs non-AD = 3,54 + 1,45 p = 0,015). One of the subjects with an AD metabolic pattern tested positive for amyloid under an ¹¹C-PiB-PET examination.

Conclusions: Dystonia and apraxia of speech were most closely related to a non-AD and myoclonus to an AD functional pattern of CBS. Individuals with an AD pattern presented with lower ACE-R and MMSE and higher HY scale scores. Functional nuclear imaging shows a potential to predict the different CBS variants while depicting their specific functional patterns.