Background and Aim: Complex regional pain syndrome (CRPS) is a highly refractory chronic pain condition that affects the extremities following an injury. CRPS manifests as severe pain, hyperalgesia, allodynia, and a constellation of autonomic, trophic, and psychological symptoms that reduce quality of life. Although the pathophysiology of CRPS remains unclear, dysfunctional skin-resident and infiltrating immune cells are thought to contribute to maladaptive pain signalling by sensitising peripheral nociceptors. In particular, Langerhans cell numbers are increased in acute-phase CRPS-affected skin but reduced in chronic-phase disease (Li et al., 2018, J. Neuroinflammation; Osborne et al., 2015, Eur. J. Pain). Due to the historical use of standard immunohistochemical techniques, high-parameter investigations on CRPS-affected skin are absent. The aim of the current study was to systematically characterise all cutaneous leukocytes in chronic-phase CRPS-affected (n = 13), contralateral unaffected (n = 13), and healthy control (n = 13) skin using high-parameter immunophenotyping with Imaging Mass CytometryTM (IMCTM).
Methods: Zamboni’s-fixed, paraffin-embedded (ZFPE) 3 mm skin punch biopsies were obtained from both hands of patients with chronic-phase CRPS (≥6 months post-diagnosis) and healthy controls. Tissue specimens were sectioned at 7 μm and immunolabelled with a panel of heavy metal isotope-conjugated antibodies targeting resident immune cell populations. Acquisition was performed on a HyperionTM+ Imaging System (Standard BioTools) and data was analysed using cell detection and classification algorithms in QuPath and expressed as mean count ±SEM cells/mm2.