NEFL and amyotrophic lateral sclerosis: There was a significant group effect of CSF-NFL levels when comparing PPMS to ALS (p < 0.001), and post-hoc analysis revealed lower median [range] levels for PPMS compared to ALS [1724 (799–4275) pg/ml vs. 10238 (2610–35138) pg/ml, p < 0.001], ALS compared to HC [1202 (612–2934) pg/ml, p < 0.001] and PPMS compared to HC (p = 0.015) Figure 1.