Myeloma is caused by the excessive production of abnormal plasma cells in the bone marrow. Plasma cells are immune cells that normally are responsible for producing antibodies that fight off infectious agents. Cancerous plasma cells, called myeloma cells, instead produce an abnormal antibody that can cause complications.
Bone marrow is the soft tissue inside bones where such myeloma cells can be found. Because these cells often appear in the marrow of multiple bones, the disease is also called multiple myeloma.
The condition is known to primarily affect blood cells, bones, and kidneys. However, the age of onset of symptoms, and their occurrence and progression, can vary among different individuals with this type of cancer.
About 85% of people with myeloma have some type of bone damage, which can be associated with lesions directly caused by myeloma cell masses or linked to the cells’ abnormal production of molecules that promote bone breakdown.
With weakened bones, patients often experience bone pain — especially in the back, ribs, hips, and skull —, and have an increased risk of fractures.
Abnormally high levels of calcium in the blood, a condition called hypercalcemia, are common in patients due to excessive bone destruction. Symptoms of hypercalcemia include increased thirst and urination, lack of appetite, nausea, abdominal pain, constipation, weakness/fatigue, and confusion. In severe cases, hypercalcemia can lead to kidney failure, coma, or cardiac arrest.
People with myeloma often have a shortage of blood cells, including oxygen-transporting red blood cells, infection-fighting white blood cells, and clotting-promoting platelets. This is due to the rapid accumulation of cancerous cells in the bone marrow — where blood cells are produced — that impairs the generation of healthy cells.
Notably, low red blood cell counts, or anemia, can cause general weakness, shortness of breath, dizziness, and abnormal paleness or lack of color in the skin, while low platelet counts, or thrombocytopenia, affect blood clotting and can make patients bruise easily and bleed profusely from even minor injuries. A deficiency in white blood cells, also known as leukopenia, weakens the immune system and increases the risk of infection.
Myeloma patients are 15 times more susceptible to infections than people without the condition, and may be slow to respond to appropriate treatment. Pneumonia is a very common infection in these patients.
Problems involving the kidneys affect more than half of patients at some point in the course of their disease. These complications are associated with kidney overwork, as these organs filter blood with excess levels of calcium and M protein — the abnormal antibody produced by myeloma cells.
Kidney damage may not cause any symptoms at first, but can be detected in a blood or urine test. Abnormalities in the kidneys may progress slowly or rapidly, and may eventually lead to kidney failure. Symptoms of kidney disease include weakness/fatigue, shortness of breath, and swelling in the legs.
Nervous system symptoms
If the bones of the spine are weakened by the disease, they can collapse and press on spinal nerves, a condition called spinal cord compression. This can cause sudden, severe back pain, muscle weakness and numbness in the legs and arms, and bladder and bowel dysfunction. Such symptoms should be considered a medical emergency: If not treated, spinal cord compression may result in permanent paralysis.
Some patients also may experience numbness or “pins and needles” sensations due to damage of the peripheral nerves, which control movement and sensation in the limbs, meaning the hands, feet, arms, and legs. This condition, called peripheral neuropathy, occurs because the abnormal M protein is toxic to nerves.
Other nervous system-related symptoms, such as confusion, dizziness, vision problems, and stroke-like symptoms — such as weakness on one side of the body and slurred speech — also may occur. Such symptoms also are associated with excessive levels of the M protein in the blood, which can cause it to become abnormally thick and subsequently slow blood flow to the brain.
Last updated: Dec. 14, 2021, by Marta Figueiredo PhD
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