A Substudy of LY4256984 in Participants With Sporadic Amyotrophic Lateral Sclerosis

Participants must meet eligibility criteria in the \[L0U-MC-OLMP\] screening protocol before entry into the treatment study. Inclusion Criteria: * Have completed the main treatment period/phase as well as any off-treatment period/phase of Study OWAA, the parent study for this ISA. Exclusion Criteria: * The participant has conditions that preclude a lumbar puncture (LP), such as: * A history of clinically significant back pain, back pathology, and/or back injury (for example, degenerative disease, spinal deformity, or spinal surgery) that may predispose to complications or technical difficulty with LP. * Allergy to local anesthetics, such as lidocaine or its derivatives. * A local infection at the intended site of the LP. * Less than 100 giga per liter \[(\<100 GI/L) is equivalent to 100,000 per cubic millimeter (100,000/mm³)\] platelets or clinically significant coagulation abnormality or significant active bleeding, or * Currently receiving treatment with an anticoagulant, antiplatelet agent, or other drug that affects coagulation or platelet function. Low dose (according to local medical guidelines) aspirin is permitted.