CHRM2 and complex regional pain syndrome: In the acute phase of CRPS, elevated levels of pro-inflammatory cytokines—particularly tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6)—appear, alongside neuropeptides such as substance P and calcitonin gene-related peptide (CGRP), as well as autoantibodies against β2-adrenergic and M2-muscarinic receptors [60,113,114].