What is crab myeloma?

The term "crab myeloma" is not a recognized medical diagnosis for a specific disease. Instead, it most likely refers to the CRAB criteria, an important acronym used in the medical field to summarize the most typical clinical manifestations of multiple myeloma, a type of cancer that affects plasma cells. These criteria are crucial for distinguishing active, symptomatic multiple myeloma from less severe conditions like monoclonal gammopathy of undetermined significance (MGUS) or smoldering myeloma.

Understanding the CRAB Criteria in Multiple Myeloma

The acronym CRAB stands for four significant symptoms that indicate symptomatic multiple myeloma:

• Calcium elevation (Hypercalcemia)
• Renal impairment (Renal failure)
• Anemia
• Bone lesions (Bone disease)

Let's delve into each component:

C: Hypercalcemia

Hypercalcemia refers to an abnormally high level of calcium in the blood. In multiple myeloma, this occurs because the abnormal plasma cells can cause increased bone breakdown, releasing calcium into the bloodstream. Symptoms can include:

• Excessive thirst
• Frequent urination
• Nausea and vomiting
• Constipation
• Fatigue and weakness

R: Renal Impairment

Kidney damage or renal failure is a common complication in multiple myeloma. The abnormal proteins produced by myeloma cells (paraproteins) can accumulate in the kidneys, leading to damage. Elevated calcium levels can also further impair kidney function. Signs of renal impairment may include:

• Swelling in the legs, feet, or ankles
• Fatigue
• Shortness of breath
• Reduced urine output

A: Anemia

Anemia, a condition characterized by a low red blood cell count, is frequently observed in multiple myeloma patients. This can result from the myeloma cells crowding out normal blood-forming cells in the bone marrow, chronic inflammation, or kidney dysfunction affecting red blood cell production. Common symptoms include:

• Fatigue
• Weakness
• Pale skin
• Shortness of breath
• Dizziness

B: Bone Disease

Bone disease is a hallmark of multiple myeloma, often leading to bone pain, fractures, and spinal cord compression. The cancerous plasma cells stimulate osteoclasts (cells that break down bone) and suppress osteoblasts (cells that build bone), leading to lytic lesions (areas of bone destruction) and overall bone weakening. Manifestations of bone disease include:

• Persistent bone pain, especially in the back, ribs, or hips
• Pathological fractures (fractures occurring from minimal trauma)
• Spinal cord compression, which can cause numbness, weakness, or paralysis

Clinical Significance of the CRAB Criteria

The presence of one or more CRAB symptoms, along with evidence of clonal plasma cells in the bone marrow or a myeloma-defining event, is crucial for diagnosing symptomatic multiple myeloma that requires treatment. Without these symptoms, a patient might be classified as having MGUS or smoldering myeloma, which typically do not require immediate treatment but rather careful monitoring. The CRAB criteria are vital for:

• Diagnosis: Confirming active, symptomatic multiple myeloma.
• Prognosis: The severity and number of CRAB symptoms can influence the patient's prognosis and treatment approach.
• Treatment Initiation: Their presence usually indicates the need for anti-myeloma therapy.

In summary, while "crab myeloma" is not a specific disease, the CRAB criteria are fundamental to understanding and diagnosing the active, symptomatic form of multiple myeloma, guiding clinicians in determining when treatment is necessary for this complex blood cancer.