Multiple myeloma

Multiple myeloma (myelomatosis; plasma cell myeloma) is a plasma cell tumor that produces monoclonal immunoglobulin that invades and destroys nearby bone.

The most common manifestations of the disease are bone pain, renal failure, hypercalcemia, anemia, and recurrent infections. Diagnosis requires the presence of M-protein (often present in urine and absent in serum), destructive changes in bones, determination of light chains in urine, and increased plasma cell counts in bone marrow. Bone marrow biopsy is usually required. Specific therapy includes standard chemotherapy (usually with alkylating agents, glucocorticoids, anthracyclines, thalidomide) and high-dose melphalan with autologous peripheral blood stem cell transplantation.

The incidence of multiple myeloma is 2 to 4 per 100,000 population. The male to female ratio is 6:1, and most patients are over 40 years of age. The incidence in blacks is twice as high as in whites. The etiology is unknown, although chromosomal and genetic factors, radiation, and chemical compounds play a role.

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Pathophysiology of multiple myeloma

Plasma cell tumors (plasmacytomas) produce IgG in about 55% and IgA in about 20% of patients with multiple myeloma. Bence Jones proteinuria, which is the presence of free monoclonal K or X light chains in the urine, is found in 40% of these patients. In 15-20% of patients, plasma cells secrete only Bence Jones protein. These patients have a higher incidence of bone destruction, hypercalcemia, renal failure, and amyloidosis than other patients with myeloma. IgD myeloma occurs in about 1% of cases.

Diffuse osteoporosis or localized destruction of bone tissue develops most often in the pelvic bones, spine, ribs, and skull. The lesions are caused by replacement of bone tissue by a spreading plasmacytoma or by activation of osteoclasts by cytokines secreted by malignant plasma cells. Osteolytic lesions are usually multiple, but solitary intraosseous tumors are sometimes found. Extraosseous plasmacytomas are rare, but can be found in any tissue, especially the upper respiratory tract.

Hypercalcemia and anemia are usually present. Renal failure (myeloma kidney) is common, which is caused by filling of the renal tubules with protein masses, atrophy of the epithelial cells of the tubules, and development of interstitial fibrosis.

Increased susceptibility to bacterial infections is due to decreased production of normal immunoglobulin and other factors. Secondary amyloidosis occurs in 10% of patients with myeloma, most often in patients with Bence Jones proteinuria.

Symptoms of Multiple Myeloma

Persistent bone pain (especially in the spine and chest), renal failure, and recurrent bacterial infections are the most common manifestations of multiple myeloma. Pathological fractures are common. Vertebral destruction may result in spinal cord compression and paraplegia. The predominant symptom is often anemia, which may be the only reason for examining the patient; some patients have manifestations of hyperviscosity syndrome (see below). Peripheral neuropathy, carpal tunnel syndrome, abnormal bleeding, and symptoms of hypercalcemia (eg, polyuria, polydipsia) are common. Lymphadenopathy and hepatosplenomegaly are uncommon in patients with multiple myeloma.

Diagnosis of multiple myeloma

Multiple myeloma is suspected in patients over 40 years of age with unexplained bone pain (especially at night or during rest), other typical symptoms, or laboratory abnormalities such as elevated protein levels in the blood and urine, hypercalcemia, renal failure, or anemia. Evaluation includes routine blood counts, protein electrophoresis, radiographic examination, and bone marrow examination.

Variants of manifestations of multiple myeloma

Form	Characteristic
Extramedullary plasmacytoma	Plasmacytomas are found outside the bone marrow.
Solitary bone plasmacytoma	A single bone lesion of plasmacytoma, which usually produces M protein
Osteosclerotic myeloma (POEMS syndrome)	Polyneuropathy (chronic inflammatory polyneuropathy), organomegaly (hepatomegaly, splenomegaly, lymphadenopathy), endocrinopathy (eg, gynecomastia, testicular atrophy), M-protein, skin changes (eg, hyperpigmentation, increased hair growth)
Non-secretory myeloma	Absence of M-protein in serum and urine, presence of M-protein in plasma cells

Standard blood tests include a complete blood count, ESR, and blood chemistry. Anemia is present in 80% of patients, usually normocytic-normochromic with the formation of multiple agglutinates, usually including 3 to 12 red blood cells.

The white blood cell and platelet counts are usually normal. BUN, serum creatinine, and uric acid levels are often elevated, and the ESR may exceed 100 mm/h. The anion gap is sometimes low. Hypercalcemia is present at diagnosis in 10% of patients.

Serum protein electrophoresis is performed and, if no definitive result is obtained, 24-hour urine concentrate protein electrophoresis is performed. Serum protein electrophoresis detects M-protein in 80-90% of patients. The remaining 10-20% of patients usually detect free monoclonal light chains (Bence Jones protein) or IgD. In these patients, urine protein electrophoresis almost always detects M-protein. Immunofixation electrophoresis identifies the immunoglobulin class of M-protein and often detects light chain protein if serum protein immunoelectrophoresis was false-negative. Immunofixation electrophoresis is recommended if serum protein electrophoresis was negative and there is a strong suspicion of myeloma.

Radiographic examination includes general images of the skeletal bones. In 80% of cases, there is diffuse osteoporosis or lytic changes of rounded bones. Radionuclide bone scanning is usually not informative. MRI can provide a more detailed picture and is recommended if there is pain and neurological symptoms and no data on conventional radiography.

Bone marrow aspiration and biopsy are also performed, which reveal diffuse distribution or accumulation of plasma cells, indicating the presence of a bone marrow tumor. Bone marrow damage is usually uneven and more often an increased number of plasma cells with varying degrees of maturation is determined. Sometimes the number of plasma cells is normal. The morphology of plasma cells does not depend on the class of immunoglobulin synthesized.

In a patient with serum M-protein, there is reason to suspect myeloma if the Bence Jones proteinuria level is greater than 300 mg/24 h, osteolytic lesions (without evidence of metastatic cancer or granulomatous disease), and the presence of elevated plasma cells in the bone marrow.

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Treatment of multiple myeloma

Patients require extensive supportive care. Outpatient supportive care helps maintain bone density. Analgesics and palliative doses of radiation therapy (18-24 Gy) can relieve bone pain. However, radiation therapy may interfere with chemotherapy. All patients should also receive bisphosphonates, which reduce the risk of skeletal complications, relieve bone pain, and have antitumor activity.

Adequate hydration is the prevention of renal damage. Even patients with long-term, massive Bence Jones proteinuria (10-30 g/day) can preserve renal function if they maintain a urine output of more than 2000 ml/day. In patients with Bence Jones proteinuria, dehydration accompanying the administration of high-osmolar intravenous contrast can cause acute renal failure.

Hypercalcemia is treated with ample hydration and bisphosphonates, sometimes with prednisolone 60-80 mg orally daily. Although most patients do not require allopurinol, 300 mg daily is indicated in the presence of renal failure or symptoms of hyperuricemia.

Prophylactic vaccination against pneumococcal infection and influenza is indicated. Antibiotics are prescribed for documented bacterial infections and routine prophylactic antibiotics are not recommended. Prophylactic intravenous immunoglobulin may reduce the risk of infectious complications and is usually prescribed to patients with frequent recurrent infections.

Recombinant erythropoietin (40,000 U subcutaneously 3 times a week) is used in patients with anemia that is not corrected by chemotherapy. If anemia leads to cardiovascular disorders, red blood cell transfusions are used. If hyperviscosity syndrome develops, plasmapheresis is performed. Chemotherapy is indicated to reduce serum or urinary M-protein. Postcytostatic neutropenia can contribute to the development of infectious complications.

Standard chemotherapy usually consists of courses of oral melphalan [0.15 mg/(kg x day) orally] and prednisolone (20 mg 3 times a day) every 6 weeks, with response assessed after 3-6 months. Polychemotherapy can be carried out using various regimens with intravenous administration of drugs. These regimens do not improve long-term survival compared with the combination of melphalan and prednisolone, but may provide a more rapid response in patients with renal dysfunction. Autologous hematopoietic stem cell transplantation is indicated for patients younger than 70 years with adequate cardiac, hepatic, pulmonary, and renal function with stable disease or a good response after several courses of standard chemotherapy. These patients receive initial chemotherapy with vincristine, doxorubicin, and dexamethasone or dexamethasone with thalidomide. When myeloid growth factor administration is necessary, drugs that suppress bone marrow function, alkylating agents, and nitrosoureas are not prescribed. Allogeneic transplantation with non-myeloablative conditioning regimens (e.g., low-dose cyclophosphamide and fludarabine or radiotherapy) may improve disease-free survival to 5-10 years in some patients due to decreased toxicity and the presence of an immune allogeneic anti-myeloma effect. This method is indicated for patients under 55 years of age with good physiological reserve. In relapsed or refractory myeloma, new drugs (thalidomide, immunomodulatory drugs, proteasome inhibitors) are used; the efficacy of these drugs as first-line therapy is being studied.

Maintenance therapy is with non-chemotherapeutic drugs, including interferon, which provide long-lasting effects but have some side effects. The use of glucocorticoids as maintenance therapy is being studied.

Prognosis for multiple myeloma

Multiple myeloma is a progressive disease with median survival of about 3-4 years with standard chemotherapy and about 4-5 years with high-dose chemotherapy and stem cell transplantation. Treatment improves quality of life and life expectancy in 60% of patients. Unfavorable prognostic signs at diagnosis include high serum or urinary M-protein levels, elevated serum beta ₂ -microglobulin levels (> 6 μg/ml), diffuse bone lesions, hypercalcemia, anemia, and renal failure.