IC‐P‐112: Altered intrinsic functional connectivity of default mode network in a patient with posterior cortical dysfunction syndrome

Abstract

Dysfunction of brain's Default Mode Network (DMN) has been increasingly described in patients with neurodegenerative diseases, but little is known about DMN's intrinsic functional connectivity (IFC) in Posterior Cortical Dysfunction (PCD) syndrome. We report a 56 year-old woman with PCD syndrome (MMSE = 24, CDR = 0.5) with visuospatial and anxiety complaints, confirmed by neuropsychological assessment. High-resolution Magnetic Resonance Imaging (MRI) was performed using a 3.0 T scanner (Philips - Achieva). T1 - and T2-weighted images were acquired in axial, coronal, and sagittal planes with thin slices. She also underwent a 10-minute task-free functional MRI (fMRI), being instructed only to remain awake with her eyes closed. We used FSL's Melodic Independent Component Analysis (ICA) - http://www.fmrib.ox.ac.uk/fsl/ to study fMRI images in order to verify which brain regions were spontaneously active in the absence of a task. In addition, she underwent brain SPECT and the results were compared with structural and functional MRI. Neuropsychological assessment showed significant dysfunction in visuospatial skills like constructive apraxia, dyscalculia, problems with mental rotation of figures and simple logico-grammatical sentences comprehension. She also performed poorly in verbal episodic memory tests and attention, but to a lesser extent than visuospatial abilities. Concerning structural MRI, we found a very mild atrophy in parietal cortex, more on the right side. IFC analysis showed much less spontaneous activation in traditional DMN areas like precuneus and bilateral inferior parietal cortical regions. We also found less activation in ventromedial prefrontal cortex, but to a lesser extent than in the posterior DMN subsystem. Brain SPECT showed marked hypoperfusion in parieto-occipital cortex, more on the right side. We showed that IFC analysis was efficient to detect DMN dysfunction, especially in its posterior subsystem in this patient. Disrupted connectivity in parieto-occipital areas may be related to the visuospatial problems presented by this patient. These findings are in accordance with the marked hypoperfusion showed in the brain SPECT and may precede cortical atrophy. As far as we know, this is the first report of IFC analysis in PCD syndrome.