Monoclonal gammopathy of undetermined significance (MGUS) is a condition in which an atypical protein is found in the blood. The protein is called monoclonal protein or M protein.

This protein is made in the soft, blood-producing tissue in the center of bones. This blood-producing tissue is bone marrow. Monoclonal gammopathy of undetermined significance occurs most often in older men.

MGUS usually causes no problems. But sometimes it can lead to more-serious diseases. These include some forms of blood cancer.

People who have high amounts of this protein in the blood need regular checkups. That's so they can get earlier treatment if the condition gets worse. If it doesn't get worse, MGUS doesn't need treatment.

People with monoclonal gammopathy often don't have symptoms. Some people have a rash or nerve problems, such as numbness or tingling. A blood test for another condition might find MGUS by chance.

Experts don't know what causes MGUS. Changes in genes and being around certain chemicals, such as those used to kill pests, appear to play a role.

Factors that increase your risk of developing MGUS include:

• Age. The average age at diagnosis is 70 years.
• Race. Africans and Black Americans are more likely to get MGUS than white people are.
• Sex. MGUS is more common in men.
• Family history. Having family members with MGUS might increase the risk.

Each year, about 1% of people with MGUS get certain types of blood cancers or other serious diseases, such as:

• Multiple myeloma.
• Light chain amyloidosis.
• Waldenstrom macroglobulinemia.
• Lymphoma.

Other issues linked to MGUS include broken bones, blood clots, kidney problems, and damage to nerves outside of the brain and spinal cord, also known as peripheral neuropathy.

Because MGUS usually causes no symptoms, people who have it usually find out by chance during blood tests for other reasons. After that, other tests might include:

• More blood tests. These can help rule out other causes of higher protein levels. And they can check for kidney damage.
• Urine tests. Urine samples taken over 24 hours can help find if the atypical protein is in the urine. They also can check for kidney damage.
• Imaging tests. For people with bone pain, an, MRI or positron emission tomography (PET) scan can look for problems with bones from MGUS. They also might need a test to measure bone mass, also known as bone density.
• Bone marrow test. A hollow needle removes a piece of bone marrow from the back of one of the hipbones for study. This usually is only for those at risk of getting a more serious disease or other problems linked to MGUS.

MGUS doesn't require treatment. But your health care provider is likely to have you get regular checkups to watch the condition. Checkups likely will start six months after your diagnosis.

Watchful waiting

For those at high risk of MGUS leading to a more serious condition, more-frequent checkups can watch the disease. That way, treatment can start as soon as possible if it's needed.

Symptoms to watch for include:

• Bone pain.
• Tiredness or weakness.
• Weight loss without trying.
• Fever or night sweats.
• Headache, dizziness, nerve pain, or changes in vision or hearing.
• Bleeding.
• Anemia or other blood irregularities.
• Swollen lymph nodes, liver or spleen.

Medicines

Medicine for the bone-thinning disease known as osteoporosis increase bone mass. Examples include alendronate (Fosamax), risedronate (Actonel, Atelvia), ibandronate and zoledronic acid (Reclast, Zometa).

Your health care provider might refer you to someone who specializes in blood disorders, also known as a hematologist.

Here's information to help you get ready for your appointment.

What you can do

Ask a family member or friend to go with you. Someone who's with you can help you remember the information you get.

Make a list of:

• Your symptoms and when they began. Include symptoms that don't seem linked to the reason you made the appointment.
• Key information about you, including other illnesses you or people in your family have had.
• All medicines, vitamins or supplements you take, including doses.
• Questions to ask your health care provider.

For MGUS, basic questions to ask your provider include:

• What tests do I need?
• Do I need to do something to get ready for tests?
• How often do I need to come back?
• Should I start treatment or change my lifestyle?
• I have other health conditions. How can I best manage these conditions together?

Be sure to ask all the questions you have.

What to expect from your doctor

Your health care provider is likely to ask you questions, including:

• Do your hands or feet tingle or feel numb?
• Do you have the bone-thinning disease known as osteoporosis?
• Has someone in your family had MGUS?
• Have you ever had a blood clot?
• Have you ever broken a bone?
• Have you had cancer?