Plasmapheresis (plasma exchange) is one of several treatment options for people with myasthenia gravis (MG), a rare autoimmune disorder which causes weakness in the voluntary muscles, typically those controlling eye movement, vision, chewing, swallowing, and breathing.
MG is caused by an abnormal antibody in the blood which prevents a component of nerve cells, a neurotransmitter called acetylcholine, from communicating with the muscles and telling them to contract. In people with MG, muscles don’t simply tire but grow weaker with repeated use. The muscles will recover with rest but, in advanced cases, weakness becomes pronounced and patients have difficulty sustaining movement. At its worse, MG can affect swallowing and breathing to the extent that these symptoms become life threatening.
The purpose of plasmapheresis is to filter the antagonist from the blood. First, whole blood is withdrawn from the patient, from 100 to 300 milliliters depending on the extraction method. Next, the liquid portion of the blood, plasma, is separated from other blood components through use of a centrifuge. Finally, the treated blood plasma is returned to the patient and, through the process of blood circulation, distributed throughout the body.
Plasmapheresis sometimes involves the use of an automated centrifuge system. In this process, the filtered blood plasma is discarded and a mixture of red blood cells and either donor plasma or albumin is returned to the patient. Another process, membrane plasma filtration, incorporates a secondary filter, such as polypropylene, to completely remove the antibody. Plasmapheresis performed using this method skips a step, allowing for return of the filtered plasma directly to the patient.
Since the beneficial effects of plasmapheresis are often short-term (generally two weeks), a regiment of treatments over a period of several weeks is usually prescribed, typically on an outpatient basis. Multiple treatments can also be costly and, as with any invasive medical procedure, plasmapheresis is not without risk. A dangerous drop in blood pressure can occur and, since anticoagulants are used during treatment, so can uncontrolled bleeding. Sometimes, peripheral veins in a patient’s arms or legs cannot support the procedure. In this case, a catheter must be inserted into the chest, thus exposing the patient to the added risk of infection.
These risks aside, plasma exchange therapy offers the quickest short-term method for removing harmful antibodies from the blood. When used in conjunction with immune suppression therapy and indicated medications, such as prednisone, plasmapheresis is a vital component in the treatment and control of myasthenia gravis.