Efficacy and Safety of Cyclophosphamide in Amyotrophic Lateral Sclerosis

The goal of this clinical trial is to learn whether cyclophosphamide (CTX) combined with standard treatment can slow disease progression in adults with amyotrophic lateral sclerosis (ALS). It will also evaluate the safety and tolerability of CTX. The main questions it aims to answer are: 1. Does CTX combined with standard treatment reduce the decline in ALS Functional Rating Scale-Revised (ALSFRS-R) scores over 48 weeks compared with standard treatment alone? 2. What medical problems and side effects do participants have while receiving CTX? 3. Are markers of neuroinflammation and immune activity, including TSPO-PET, neurofilament light chain (NfL), upper motor neuron burden, electrophysiological measures, immune cell profiles, and autoantibodies, associated with treatment response? Researchers will compare CTX combined with standard treatment with standard treatment alone to see whether CTX can slow the progression of ALS. Participants will: 1. Be randomly assigned to receive CTX plus standard treatment or standard treatment alone 2. Receive CTX treatment for up to 36 weeks if assigned to the CTX group 3. Visit the study center regularly for clinical assessments, blood tests, lung function tests, electrophysiological tests, and other safety evaluations 4. Complete assessments of physical function, muscle strength, respiratory function, and quality of life 5. Undergo biomarker assessments, including TSPO-PET imaging and NfL testing 6. Be followed for 48 weeks during the main study period and for up to 96 weeks for long-term outcomes and safety