Background Magnetic resonance imaging (MRI) of the brain and cervical spinal cord is often performed in diagnostic evaluation of suspected motor neuron disease/amyotrophic lateral sclerosis (MND/ALS). Analysis of MRI-derived tissue damage metrics in a common domain facilitates group-level inferences on pathophysiology. This approach was applied to address competing hypotheses of directionality of neurodegeneration, whether anterograde, cranio-caudal dying-forward from precentral gyrus or retrograde, dying-back. Methods In this cross-sectional study, MRI was performed on 75 MND patients and 13 healthy controls. Precentral gyral thickness was estimated from volumetric T1-weighted images using FreeSurfer, corticospinal tract fractional anisotropy (FA) from diffusion tensor imaging using FSL, and cross-sectional cervical cord area between C1-C8 levels using Spinal Cord Toolbox. To analyse these multimodal data within a common domain, individual parameter estimates representing tissue damage at each corticospinal tract level were first converted to z-scores, referenced to healthy control norms. Mixed-effects linear regression models were then fitted to these z-scores, with gradients hypothesised to represent directionality of neurodegeneration. Results At group-level, z-scores did not differ significantly between precentral gyral and intracranial corticospinal tract tissue damage estimates (regression coefficient − 0.24, [95% CI − 0.62, 0.14], p = 0.222), but step-changes were evident between intracranial corticospinal tract and C1 (1.14, [95% CI 0.74, 1.53], p < 0.001), and between C5 and C6 cord levels (0.98, [95% CI 0.58, 1.38], p < 0.001). Discussion Analysis of brain and cervical spinal MRI data in a common domain enabled investigation of pathophysiological hypotheses in vivo. A cranio-caudal step-change in MND patients was observed, and requires further investigation in larger cohorts.
A 24-year-old female presented with a 10-year history of mottled patches on the limbs. These were asymptomatic and persisted on rewarming. She was otherwise well with no past history or constitutional symptoms. Examination revealed reticulate erythematous to cyanotic patches forming incomplete rings, consistent with livedo racemosa. Histology showed a lymphocytic vasculitis with 1+ granular deposits of C3, IgM and fibrin on direct immunofluorescence. Clinical systemic review, antiphospholipid, hypercoagulability and autoimmune workups were unremarkable. This was consistent with the diagnosis of lymphocytic thrombophilic arteritis, a medium vessel vasculitis typically without systemic involvement. This presents with livedo racemosa, which is differentiated from livedo reticularis by the presence of larger broken rings that do not reverse with warming. Unlike livedo reticularis which may be physiological, livedo racemosa is always pathological. Critically, a skin biopsy should include the centre of the ring in order to sample the feeding artery.
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