Multimodal investigation of autonomic dysfunction in systemic sclerosis: from clinical assessments to molecular insights

Given some preliminary findings of a possible pathogenic role for autonomic nervous system (ANS) in systemic sclerosis (SSc), the aim of the present PhD thesis was to obtain a complete characterization on how autonomic dysfunction affects SSc, with a look in particular at the very early preclinical forms (VEDOSS) and forms at onset (less than 6 months of disease duration), in order to have a complete picture also on the timing of dysautonomic alterations. At the beginning of this project, we started aiming to conduct a scoping review with the dual purpose of mapping the research done in this field so far and bringing out some pathogenetic hypotheses to inform future research efforts. Our scoping review identified and summarized the findings of 109 studies addressing pathogenesis, clinical presentation and diagnostic assessment of autonomic dysfunction in SSc. Cardiovascular system and cutaneous samples were identified as the most suitable fields for a complete dysautonomic assessment. Moreover, the role of brain derived neurotrophic factor (BDNF) was suggested as a possible link between autoimmunity and dysautonomia. Given a lack in reliable dysautonomic parameters for microcirculation, we took the concept of proximal-distal gradient of perfusion (PDG) and developed a formula for its quantification using laser speckle contrast analysis. We tested this novel parameter in 94 SSc patients and 47 healthy controls (HC), its consistency having significantly lower values in the former. We then compared SSc with primary Raynaud’s phenomenon and found no differences. This finding, added to other reports of no changes after vasoactive therapies, strengthens the role of PDG as a surrogate index of digital autonomic dysfunction. We then moved to a complete assessment of autonomic dysfunction in SSc at the whole cardiovascular level and with histology data from skin samples. We enrolled 56 SSc patients who underwent the investigation of the following dysautonomic parameters: the previously cited PDG for microcirculation, serum neuro-hormones, ventilation/CO2 production slope as assessed by cardiopulmonary exercise test, Holter ECG for the assessment of heart rate variability of both time and frequency domains, baroreceptor sensitivity and polysomnography. Immunohistochemical reactions were used to investigate skin samples for the presence of nerve fibers positive for acetylcholinesterase, tyrosine hydroxylase and substance P, comparing the results with HC. We demonstrated an extensive impairment of all the cardiovascular parameters, without relevant differences between VEDOSS and SSc as well as between forms at onset and forms with longer disease duration. The same was found in skin biopsies, where acetylcholinesterase and substance P were significantly reduced in SSc patients compared to HC, without differences regarding clinical form and disease duration. These findings suggest reconsidering ANS dysfunction as one of the initial key pathogenetic elements of SSc, rather than as a simple consequence of vasculopathy and fibrosis. Finally, we investigated BDNF serum concentrations and histological presence comparing SSc and HC. Serum BDNF was reduced in patients with vasculopathy and skin samples from some SSc patients had a significantly reduced expression of BDNF fibers in the dermis, a finding that links this molecule to the other pathogenic events occurring in SSc.