In this study we conduct a rapid review to (1) examine the landscape of neurodegenerative fluid biomarkers in the context of progressive forms of MS and (2) qualitatively describe relative measures of a proposed marker of neurodegeneration and progression, CSF NfL, in progressive forms of MS to determine if CSF NfL would be useful in differentiating clinical phenotypes of progressive MS. The gene discussed is NEFL; the disease is myeloid sarcoma.