The short answer
Multiple myeloma symptoms are often summarized as CRAB: high calcium, kidney (renal) problems, anemia, and bone damage. New severe back pain with leg weakness or a change in bladder or bowel control is an emergency: call 911 or go to an emergency department.
Multiple myeloma symptoms are often summarized with the acronym CRAB: high Calcium, Renal (kidney) problems, Anemia, and Bone disease.
Bone pain, often in the back, hips, or skull, and bones that break unusually easily, are among the most common symptoms.
New, severe back pain along with leg weakness, numbness, or a change in bladder or bowel control is an emergency that can mean spinal cord compression and needs 911 or an emergency department, not a clinic call.
High blood calcium (hypercalcemia) can cause extreme thirst, confusion, constipation, and drowsiness, and needs prompt medical attention.
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The full explanation.
Get help right now if
- You have new, severe back pain along with leg weakness, numbness, tingling, or a change in bladder or bowel control. Call 911 or go to an emergency department. This combination can mean spinal cord compression, and delay can leave permanent nerve damage, so it needs treatment now rather than a call to the clinic. See Spinal Cord Compression During Cancer Care.
- You have a fever of 100.4°F (38°C) or higher during or after treatment, especially with a known low white blood cell count. Go to an emergency department, or call 911 if you also feel faint, shaky or short of breath. NCI describes infection during cancer treatment as life threatening and needing urgent medical attention. See Neutropenic Fever During Cancer Treatment.
- You have sudden confusion, dizziness, or vision changes. Emergency care. This can signal hyperviscosity, thickened blood affecting circulation to the brain.
- You have extreme thirst with confusion, severe drowsiness, or significant weakness. This can be severe hypercalcemia (high blood calcium). Confusion or drowsiness means an emergency department; thirst and weakness on their own still need a same-day call.
- A bone breaks with little or no clear injury, or pain suddenly increases at a specific bone. Call your team the same day.
None of these should wait for a scheduled appointment. Use your care team's emergency plan, and if you cannot reach them quickly, go to an emergency department.
The simple version
Multiple myeloma is a cancer of plasma cells, a type of white blood cell that normally makes antibodies to fight infection. Abnormal plasma cells build up in the bone marrow. They crowd out healthy blood cells, produce an abnormal protein, and can damage bone and kidneys. Doctors often summarize the main effects using the acronym CRAB.
CRAB stands for Calcium (high), Renal (kidney problems), Anemia, and Bone disease: the four main types of organ damage myeloma can cause.
CRAB, in plain language
Calcium. Damaged bone releases calcium into the blood faster than the kidneys can clear it. This causes hypercalcemia, or high blood calcium. It can cause extreme thirst, frequent urination, dehydration, constipation, abdominal pain, loss of appetite, weakness, and drowsiness or confusion.
Renal, meaning kidney. The abnormal protein made by myeloma cells, along with high calcium, can damage the kidneys. Early kidney damage may cause no symptoms at all. As it progresses, it can cause weakness, shortness of breath, itching, and swelling in the legs.
Anemia. Myeloma crowds out normal blood cell production, lowering red blood cells. This causes fatigue, weakness, shortness of breath, and dizziness.
Bone disease. Bone pain, most often in the back, hips, or skull, is one of the most common myeloma symptoms. Bones can also weaken and break more easily, sometimes with only minor stress.
Other symptoms
- Low platelets, raising the risk of bruising and bleeding.
- Low healthy white blood cells, raising infection risk. Pneumonia is a particularly common infection in people with myeloma.
- Hyperviscosity: thickened blood from a high level of the abnormal protein. This can cause confusion, dizziness, and stroke-like symptoms.
- Rarely, light chain amyloidosis, where a myeloma-related protein deposits in organs. It can affect the heart, liver, tongue, skin, or nerves.
Questions to ask
- Do I currently have any CRAB features, and how are they being monitored?
- What is my calcium level right now?
- How is my bone health being tracked?
- What back or nerve symptoms mean I should go to the emergency department?
- What should I do if I develop a fever?
Sources
Words to know
Tap any term to see what it means.
Common questions
What does CRAB stand for, and why is it used?
CRAB stands for Calcium (elevated), Renal (kidney problems), Anemia, and Bone disease. It's a way doctors summarize the main organ damage caused by abnormal plasma cells (a type of white blood cell that normally makes antibodies) building up and producing an abnormal protein. Having one or more CRAB features is part of what distinguishes active multiple myeloma needing treatment from an earlier, watched precursor condition.
Why does multiple myeloma affect the bones so much?
Abnormal plasma cells in the bone marrow disrupt the normal balance of bone building and breakdown, weakening bone. This causes pain, most often in the back, hips, or skull, and makes bones more likely to fracture, sometimes with only minor stress or no clear injury at all.
What is hypercalcemia, and why is it serious?
Hypercalcemia means too much calcium in the blood, which can happen when damaged bone releases calcium faster than the kidneys can clear it. It can cause extreme thirst, frequent urination, dehydration, constipation, abdominal pain, loss of appetite, weakness, drowsiness, and confusion. Severe hypercalcemia needs prompt medical treatment.
Is back pain with multiple myeloma always an emergency?
No, ordinary bone pain from myeloma is common and usually not an emergency on its own. It becomes an emergency when new, severe back pain is combined with leg weakness, numbness, tingling, or a change in bladder or bowel control, because this combination can mean the spinal cord is being compressed by a growing area of bone damage or a soft-tissue mass. That combination needs emergency care straight away, because delay can leave permanent weakness.
Why are infections such a concern with multiple myeloma?
Multiple myeloma reduces the number of normal, working antibodies the immune system can make, and treatment can further lower blood counts. This raises the risk that an infection can progress quickly. A fever of 100.4°F (38°C) or higher during or after treatment needs emergency assessment, not watching at home.
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Last updated: 2026-08-20Next planned review: 2027-08-03
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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