To investigate the presence and specificity of SIGLEC1+ myeloid cells in inflammatory MS lesion, we analysed brain tissue sections from 4 patients with MS lesions that had clinical, radiological and histological signs of activity (gadolinium uptake on MRI imaging, presence of myelin-laden macrophages), 5 patients with secondary-progressive MS (SPMS) who died of acute non-neurologic causes and with histologically classified chronic lesions and 6 patients who died of cardiovascular or multi-organ failure. Here, SIGLEC1 is linked to myeloid sarcoma.