Multiple myeloma C.R.A.B. symptoms: Criteria, outlook, and more

What is multiple myeloma (in plain English)?

Multiple myeloma is a blood cancer that starts in plasma cellsimmune cells that normally make antibodies.
In myeloma, a single “clone” of plasma cells grows out of control and produces an abnormal antibody protein
(often called an M protein or monoclonal protein).

The trouble is less about the word “multiple” and more about the collateral damage:
myeloma cells can crowd out healthy blood-making cells in the bone marrow, disrupt bone remodeling,
and spill proteins that stress the kidneys. That’s where CRAB comes in.

CRAB, decoded: the four classic signs of myeloma-related organ damage

CRAB is an acronym used to summarize end-organ damage that can be attributed to a plasma cell disorder:
Calcium elevation (hypercalcemia), Renal (kidney) impairment,
Anemia, and Bone disease.

Quick reference: the IMWG CRAB thresholds clinicians use

Different medical resources may phrase cutoffs slightly differently, but the International Myeloma Working Group (IMWG)
has clearly defined criteria commonly used in practice.

Important nuance: CRAB findings must be attributable to the plasma cell disorder,
not explained better by something else (like dehydration from a stomach bug or anemia from iron deficiency).
That “attributable” part is why doctors can seem so obsessed with details.

The CRAB symptoms, one letter at a time

C: Hypercalcemia (high blood calcium)

Myeloma can speed up bone breakdown. When bone is broken down too quickly, calcium can spill into the bloodstream.
High calcium can affect nerves, muscles, digestion, and kidney function.

What it can feel like varies, but classic complaints include:
extreme thirst, peeing a lot, constipation, belly discomfort,
fatigue, and sometimes feeling foggy or unusually sleepy.

A practical example: someone might blame weeks of constipation and fatigue on stress, travel, or “getting older,”
only to discover on routine labs that calcium is significantly elevatedthen the workup snowballs from there.

Clinicians treat hypercalcemia urgently when it’s significant, often starting with hydration and medications that
slow bone breakdown (your team will decide what’s appropriate based on severity and kidney function).

R: Renal impairment (kidney trouble)

Kidney issues in myeloma are often driven by excess free light chainsprotein fragments that can clog
and inflame the kidneys (sometimes called “cast nephropathy” in medical speak). Dehydration, infections, and
high calcium can pile on.

The frustrating part is that early kidney injury can be quiet. You may feel “off” (more tired, less hungry) or notice
swelling, but sometimes the first clue is simply abnormal creatinine/eGFR on bloodwork.

Because kidneys are such a big deal for dosing and treatment choices, clinicians often check:
creatinine, estimated filtration rate, urine protein, and tests aimed at detecting monoclonal proteins.

A: Anemia (low red blood cells)

Anemia in myeloma often happens because the bone marrow gets crowdedmyeloma cells take up space and resources that
healthy blood cell production needs. The result can be low hemoglobin, which means less oxygen delivery to tissues.

What people often notice first: fatigue that feels out of proportion, getting winded walking up stairs,
lightheadedness, or a “battery that won’t hold a charge.” Sometimes it’s subtle until a CBC says otherwise.

Management depends on the cause and severitytreating the myeloma often improves anemia, and clinicians may also
address iron/B12/folate issues, bleeding risks, or consider transfusion in certain scenarios.

B: Bone disease (lytic lesions, fractures, and bone pain)

Myeloma can tilt the bone remodeling balance: more bone is broken down than rebuilt. This can lead to lytic lesions,
thinning bones, fractures, and persistent painoften in the back, ribs, or hips.

Imaging matters here. A plain X-ray survey can miss early lesions, so clinicians often use low-dose whole-body CT,
PET/CT, and/or MRI depending on the situation and availability.

Red-flag bone symptoms that deserve urgent evaluation include:
new severe back pain, weakness or numbness in the legs, trouble walking, or bowel/bladder changesthese can signal
spinal involvement or compression that needs immediate attention.

SLiM-CRAB: why doctors may treat myeloma even before CRAB damage appears

Historically, myeloma was treated once CRAB organ damage showed up. But research showed that some people are at very
high risk of progressing to organ damage soon, even if they don’t feel “symptomatic” yet. That’s why IMWG added
three myeloma-defining events (often shortened to SLiM) to the classic CRAB framework.

S: Sixty percent or more clonal plasma cells in bone marrow

If bone marrow testing shows ≥ 60% clonal plasma cells, that’s considered a myeloma-defining event
because the risk of near-term progression is high.

Li: Light chain ratio ≥ 100 (with an important “and also”)

Another myeloma-defining event is an involved/uninvolved serum free light chain ratio of ≥ 100,
provided the involved light chain level is at least 100 mg/L.

M: MRI focal lesions (more than one, and not tiny)

More than one focal lesion on MRI (each at least about 5 mm) can also qualify as a myeloma-defining event.

Bottom line: someone can be diagnosed with “active” multiple myeloma based on SLiM criteria even without CRAB damage
which can allow treatment to start before kidneys, bones, or blood counts take a major hit.

How clinicians connect the dots: tests that show the “why” behind CRAB

Diagnosing myeloma isn’t a single testit’s a combination of evidence:
plasma cell burden (often via bone marrow biopsy), monoclonal protein detection, and signs of organ involvement.
Common components include: CBC, chemistry panel (calcium/creatinine), serum and urine protein electrophoresis,
immunofixation, quantitative immunoglobulins, and serum free light chain testing.

Bone marrow testing frequently includes cytogenetics/FISH to help risk-stratify the disease, and imaging helps define
bone involvement and guide treatment decisions.

People often ask, “But I feel okaywhy all the tests?” Because myeloma can do meaningful damage quietly, especially
in the kidneys and bones. Catching problems early can change the plan.

Treatment and supportive care: addressing both myeloma and the CRAB fallout

Treatment is individualized (age, overall health, kidney function, genetics/risk profile, symptoms, and patient goals),
but modern care often includes combinations of targeted therapies and immune-based treatments, and sometimes stem cell
transplant for eligible patients.

Supportive care mapped to CRAB

• For high calcium (C): hydration and therapies that slow bone breakdown are common approaches,
  along with treating the underlying myeloma driver.
• For kidney issues (R): rapid control of free light chains is often a priority; clinicians also
  manage contributing factors (dehydration, infections, nephrotoxic meds).
• For anemia (A): treatment of myeloma plus evaluation for other contributors; transfusion may be used
  when appropriate based on symptoms and lab values.
• For bone disease (B): bisphosphonates or other bone-strengthening approaches, vitamin D/calcium
  guidance when appropriate, pain management, radiation for focal painful lesions, and orthopedic support for fracture risk.

Another big theme is infection risk. Myeloma and some treatments can lower immune defenses, so vaccination strategies,
prompt evaluation of fevers, and preventive steps may be part of the plan.

Outlook and prognosis: what “criteria” can (and can’t) tell you

CRAB and SLiM-CRAB help define when myeloma is active and needs therapy, but they don’t fully predict a person’s
long-term course. Outlook depends on many factors: disease stage, kidney function, genetics/cytogenetics, response
to therapy, and overall health.

Staging systems (like IMWG’s revised staging approach referenced in standard workups) commonly incorporate lab markers
and disease biology to estimate risk groups, and clinicians may use imaging and marrow studies to guide intensity of
therapy and monitoring.

Here’s the reassuring part: while myeloma is still often described as chronic and relapsing for many people,
treatments have advanced dramatically over the past couple of decades, and many patients live for years with good
quality of lifeespecially when complications like CRAB features are addressed quickly.

A practical way to think about it: CRAB is about damage. Modern myeloma care is increasingly about
preventing damage, controlling the cancer, and keeping people active and supported.

When to call a clinician urgently

If you have (or might have) multiple myeloma, certain symptoms should trigger prompt medical attentionespecially
because they can signal complications related to CRAB:

• New or worsening confusion, extreme drowsiness, or severe weakness (possible high calcium).
• Very low urine output, sudden swelling, or rapidly worsening kidney labs (possible renal impairment).
• Chest pain, significant shortness of breath, fainting, or severe dizziness (can be anemia or other issues).
• New severe back pain, leg weakness/numbness, or trouble walking (possible spinal involvement).
• Fever or signs of serious infection.

FAQ: common questions about multiple myeloma CRAB symptoms

Do you always have CRAB symptoms if you have myeloma?

Not always. Some people are diagnosed before classic CRAB damage appears, especially under SLiM-CRAB criteria.
Others may have subtle symptoms that are easy to attribute to everyday life until labs or imaging reveal the cause.

Can CRAB findings be caused by something else?

Yes. High calcium, kidney dysfunction, anemia, and bone pain all have many potential causes. That’s why clinicians
work to confirm that CRAB findings are linked to the plasma cell disorder and not better explained by another condition.

What’s the “most common” CRAB symptom?

There isn’t one universal first symptom. Many people notice fatigue (often tied to anemia) or persistent bone pain,
but some discover issues through routine bloodwork before symptoms feel dramatic.

Real-world experiences (extra): what the CRAB journey can feel like

The clinical criteria are neat and tidy. Real life, not so much. People rarely wake up and announce, “Good morning,
I’m having a textbook CRAB presentation today.” More often it’s a slow accumulation of “little weird things” that
finally add up to one big appointment.

A common story starts with fatigue that doesn’t match the calendar. Someone who’s always been active might notice
they’re taking longer breaks after chores, getting winded on stairs, or needing naps that feel wildly out of character.
Friends may say, “You’re just busy,” and the person may agreeuntil a routine blood test reveals anemia. That’s when
fatigue stops being a personality trait and becomes a clue.

Bone pain can be equally sneaky. Back pain is practically a modern hobby, so it’s easy to blame a desk chair,
a workout, or sleeping “wrong.” But myeloma-related bone pain can stick around, flare at night, or show up in the ribs,
hips, or spine without a clear injury. Some people describe it as deep, persistent soreness that doesn’t respond the
way typical muscle pain does. The moment imaging enters the chatX-ray, CT, PET/CT, MRIthe pain suddenly has context,
which can be both scary and validating: “I wasn’t being dramatic. Something really was going on.”

Kidney issues are often the most unfair, because they can feel invisible until they aren’t. A person may not notice
anything specificmaybe they’re slightly puffy around the ankles or they feel more nauseated than usualyet bloodwork
shows rising creatinine or worsening kidney function. Once the team explains how excess myeloma proteins can stress
the kidneys, many patients become surprisingly motivated about hydration, medication checklists, and avoiding anything
that might add extra strain. It’s not “overthinking.” It’s protecting an organ that doesn’t send many warning texts.

Hypercalcemia can be the strangest experience to describe. Some people talk about intense thirst and constant bathroom
trips; others feel constipated, weak, and mentally foggylike their brain is running on low battery mode. Family members
may notice mood changes or confusion before the patient does. When calcium normalizes, many people are shocked by how
much better they feel and how quickly the world becomes “clear” again.

Emotionally, the CRAB phase can swing between overwhelm and relief. Overwhelm because there are suddenly new words
everywhere“free light chains,” “bone marrow biopsy,” “staging,” “cycles.” Relief because the symptoms finally have an
explanation and a plan. People often say the most helpful experiences are practical ones: a nurse who explains labs in
normal language, a pharmacist who helps untangle medication timing, a physical therapist who makes movement feel safe
again, or a support group that swaps tips about fatigue and bone health without pretending everything is sunshine.

If there’s a takeaway from patient experiences, it’s this: CRAB criteria are clinical guardrails, not a definition of
a person. With modern therapy and supportive care, many people move from crisis mode to a new routineone where lab
trends and scan schedules coexist with birthdays, work, school drop-offs, and the ordinary joys of feeling like
yourself again.