They say 1 of these 3 ways generally Why Swelling Happens in MSReduced Mobility: When you sit or lie down for long periods, your calf muscles do not contract. These muscle movements normally act as a pump to push blood and lymphatic fluid back up toward your heart.Fluid Buildup: Without regular muscle action, gravity causes blood and lymphatic fluid (a condition called lymphedema) to pool in your lower extremities, leading to edema.Medication Side Effects: Certain disease-modifying therapies or other prescription drugs used to manage MS can also cause lower-leg fluid retention as a side effect.

#1 Reduced Mobility: When you sit or lie down for long periods, your calf muscles do not contract. These muscle movements normally act as a pump to push blood and lymphatic fluid back up toward your heart.