Increased cerebral integrity metrics in poliomyelitis survivors: putative adaptation to longstanding lower motor neuron degeneration

BACKGROUND: Post-polio syndrome (PPS) has been traditionally considered a slowly progressive condition that affects poliomyelitis survivors decades after their initial infection. Cerebral changes in poliomyelitis survivors are poorly characterised and the few existing studies are strikingly conflicting. OBJECTIVE: The overarching aim of this study is the comprehensive characterisation of cerebral grey and white matter alterations in poliomyelitis survivors with reference to healthy- and disease-controls using quantitative imaging metrics. METHODS: Thirty-six poliomyelitis survivors, 88 patients with ALS and 117 healthy individuals were recruited in a prospective, single-centre neuroimaging study using uniform MRI acquisition parameters. All participants underwent standardised clinical assessments, T1-weighted structural and diffusion tensor imaging. Whole-brain and region-of-interest morphometric analyses were undertaken to evaluate patterns of grey matter changes. Tract-based spatial statistics were performed to evaluate diffusivity alterations in a study-specific whiter matter skeleton. RESULTS: In contrast to healthy controls, poliomyelitis survivors exhibited increased grey matter partial volumes in the brainstem, cerebellum and occipital lobe, accompanied by increased FA in the corticospinal tracts, cerebellum, bilateral mesial temporal lobes and inferior frontal tracts. Polio survivors exhibited increased integrity metrics in the same anatomical regions where ALS patients showed degenerative changes. CONCLUSIONS: Our findings indicate considerable cortical and white matter reorganisation in poliomyelitis survivors which may be interpreted as compensatory, adaptive change in response to severe lower motor neuron injury in infancy.