MGUS is caused by monoclonal plasma cells. Monoclonal means we think they all began from the same cell.
Plasma cells are part of your immune system. When they are normal, they help you fight infection. Here’s how: When germs enter your body, special immune cells “take a bite” from them, and — with the help of other immune cells — present the pieces to the plasma cells to help them identify the enemy. The plasma cells then multiply themselves into an army and produce antibodies to kill the germs. The antibodies are made to attack those germs specifically, and fit into them like a key into a lock. (Plasma cells respond to vaccines and immunizations the same way — by making the antibodies that protect you against diseases such as the flu, measles and polio.)
As soon as the infection is gone, the plasma cells stop multiplying. Some of them go back into the bone marrow and stay there in case the germs return and they are needed again.
When plasma cells become abnormal, they do not stop multiplying, and they produce antibodies that are not targeted to specific germs, so they are useless in fighting infection.
The antibodies produced by those abnormal cells are called monoclonal proteins (M-proteins), and they can be measured in the blood and urine. If only parts of the antibodies are produced, they are called light or heavy chains.
Symptoms of MGUS
MGUS does not usually cause symptoms. However, in rare cases it can cause polyneuropathy, a type of nerve damage that can cause tingling or numbness, mostly in the arms, fingers, legs and toes, or kidney damage.
MGUS is not a disease, because most of the time it causes no symptoms, but there is a very low risk that it can progress into a symptom-causing disease. When you are evaluated at Roswell Park, your team will look at your risk factors to determine the chances that that will happen.
Tests for Diagnosing MGUS
The following tests may be required to diagnose MGUS and determine that it is not a symptom-causing disease:
- Bone marrow biopsy, to find out how many monoclonal plasma cells are in your bone marrow (This is performed only in patients with certain characteristics of MGUS.)
- A urine sample (collected over a 24-hour period) and blood draw, to find out how much M-protein is in your urine and serum.
- A blood draw, to find out how much calcium is in your blood and whether your kidneys are functioning normally.
- Magnetic Resonance Imaging (MRI) or Positron Emission Tomography and Computed Tomography (PET-CT), to find out whether there are holes in your bones (This is performed only in patients with certain characteristics of MGUS.)
Because MGUS does not cause symptoms, and the risk of developing symptoms is low, researchers agree that it does not have to be treated — only monitored with follow-up visits every six to 12 months.