A proof of concept shotgun proteomic interrogation of post‐mortem cervical spinal cord tissue derived from MS cases segregated by HLA‐DRB*15 status, identified three extracellular matrix (ECM) proteins, biglycan, decorin, and prolargin, that are overexpressed in HLA‐DRB1*15‐positive cases. Here, DCN is linked to myeloid sarcoma.