Plasma cell disorders are a group of neoplastic or potentially neoplastic diseases of hematopoietic cells known as plasma cells. Plasma cells are B cells that secrete immunoglobulins. The clinical manifestations of these disorders result from the uncontrolled and progressive proliferation of a plasma cell clone, the effect of normal bone marrow replacement, and the overproduction of specific proteins.
Plasma cell disorders are characterized by the secretion of monoclonal proteins or immunoglobulins (M protein or paraprotein). An abnormal M protein may be present when the total protein concentration in quantitative immunoglobulin values are within normal limits. The presence of an abnormal M protein is usually associated with:
- multiple myeloma
- monoclonal gammopathy of undetermined significance (MGUS)
- or Waldenström's macroglobulinemia
An M protein rarely is associated with other lymphoproliferative disorders (such as Non-Hodgkin's lymphoma) or primary amyloidosis.
Historically, an entity known as smoldering multiple myeloma has been defined, which clinically falls between MGUS and overt multiple myeloma. Smoldering multiple myeloma is generally defined as greater than 10% plasma cells in the marrow and an M serum protein of greater than 3g/dL; however, serum creatinine and calcium levels are normal.
Additionally, lytic bone lesions are absent. Although smoldering myeloma inevitably evolves into overt multiple myeloma, often, there is stability over time. Frequently, the initial therapy is observation. Because of the relative infrequency of these other plasma cell disorders, this chapter will focus solely on multiple myeloma.
The clinical manifestations of multiple myeloma can be divided into four broad categories: plasma cell growth in bone marrow and skeletal disease, immunologic abnormalities, effect of the abnormal paraprotein, and renal failure.
Plasma Cell Growth in Bone Marrow and Skeletal Disease
The most common presenting symptom of multiple myeloma is bone pain, usually involving the spine or chest. Diffuse osteoporosis is often seen radiographically. Characteristic myeloma changes are lytic lesions (rounded, punched-out areas of bone) found most commonly in vertebral bodies, the skull, ribs, humerus, and femur. Bone scans may or may not accurately reflect the destruction seen on radiographic films.
A solitary plasmacytoma--essentially, a solid tumor mass of plasma cells--is found in 2% of patients and is usually seen in a vertebral body. Plasmacytomas are conventionally treated with radiation therapy; however, despite this therapy, most patients ultimately progress to have more typical manifestations of multiple myeloma.
Most neurologic abnormalities associated with multiple myeloma result from direct extension of a skeletal tumor. Spinal cord compression is present in 10% of patients. Although peripheral neuropathies are uncommon in myeloma, they can be caused by amyloidosis, hyperviscosity, or both.
Anemia develops in most patients and is generally secondary to poor red blood cell production--either from marrow infiltration with plasma cells, or from kidney failure and resultant inappropriately low erythropoietin production.
Rouleaux are often present on the peripheral smear, resulting from the increased number of immunoglobulins in the plasma. Mild neutropenia occurs in up to 50% of patients. Thrombocytopenia is common, either from the myeloma itself or from repeated courses of chemotherapy. Plasma cell leukemia, a condition in which plasma cells predominate among the circulating white blood cells, is typically a terminal stage of multiple myeloma and is associated with short survival.
Patients with myeloma often suffer from repeated episodes of infection, similar to that seen in patients with reduced levels of immunoglobulins. Commonly, patients exhibit a reciprocal decrease in normal immunoglobulin values in the presence of an elevated M protein. An increased incidence of both gram-positive and gram-negative organisms has been reported.
Effect of Abnormal Paraprotein
Hyperviscosity syndrome results from the presence of serum proteins with high intrinsic viscosity. This is most commonly associated with immunoglobulin M (IgM) paraprotein, but may also occur with IgG or IgA paraprotein. High viscosity interferes with efficient blood circulation of the brain, kidneys, and extremities. Headache is common, and dizziness, vertigo, and symptoms of severe ischemia may result. Peripheral neuropathy may occur secondary to occlusive changes in small vessels. High levels of M protein may interfere with coagulation factors and lead to abnormal platelet aggregation and abnormal platelet function; therefore, bruising and purpura are common.
Proteinuria is present in 90% of patients with multiple myeloma, and abnormal light chains (Bence Jones protein) are found in 80% of patients. At diagnosis, the creatinine level is elevated in 50% of patients. Proximal tubules are increasingly damaged by the large protein load, and large obstructing casts frequently form within the tubules. The combination of interstitial fibrosis and hyaline casts surrounded by epithelial cells or multinucleate giant cells constitutes myeloma kidney. Additionally, hypercalcemia and hypercalciuria as well as hyperuricemia contribute to kidney damage.
Although conventional therapy cannot cure multiple myeloma, it can effect a temporary remission. Patients presenting with symptomatic skeletal lesions are initially treated with radiation therapy. Radiation therapy is also indicated for plasmacytomas that may impair the function of vital structures.
Systemic therapy is required to control the clinical manifestations of myeloma. Most investigators believe that an initial course of systemic therapy is indicated, which is generally followed by autologous stem cell transplantation. No single chemotherapeutic protocol clearly has been shown to be optimal; the historical standard regimen is a combination of melphalan and prednisone, which results in a response rate of approximately 60% to 70%.
Another popular regimen, infusional vincristine, doxorubicin, and dexamethasone (VAD), is generally well tolerated. Recent clinical trials have demonstrated that the combination of thalidomide and dexamethasone yields a 77% response rate.2,3 The National Comprehensive Cancer Network (NCCN) has delineated guidelines for the approach to the treatment of multiple myeloma at: www.nccn.org
Autologous stem cell transplantation generally consists of a collection of the patient's peripheral blood progenitor cells following stimulation by granulocyte colony-stimulating factor (G-CSF), with or without chemotherapy. The patient is then given either high-dose chemotherapy or chemotherapy with total body radiation therapy. Most investigators now use melphalan (150 mg/m2 to 200 mg/m2) as the high-dose preparative regimen of choice.
One randomized trial that compared autologous transplantation to chemotherapy found that 5-year event-free survival (28% versus 10%) and overall survival rates (52% versus 12%) were significantly higher in the transplant group.4 Another trial conducted at a single treatment center studied more than 1,000 patients who were either newly diagnosed or had limited prior treatment. For patients presenting with a low beta2-microglobulin level and without a chromosome 13 deletion, the data showed that up to 50% of patients achieved complete remission with sustained responses for 10 years.5
Although most investigators believe that autologous transplantation improves survival and event-free survival, ultimately, most patients will relapse. Efforts to reduce risk of relapse after autologous transplantation has lead to many novel therapies, including nonmyeloablative allogeneic transplantation, which attempts to generate a graft-versus-tumor effect and may be used in the older population typically affected by multiple myeloma.
Bisphosphonates are an important therapeutic tool for patients with myeloma6 because they demonstrate anti-bone resorptive activity and possess antitumor mechanisms, resulting in reduced bone pain. Bisphosphonates inhibit bone resorption and decrease IL-6 production in the bone marrow microenvironment, which suggests that they may have an anti-myeloma effect. Pamidronate and zoledronic acid normalize tumor-induced hypercalcemia and may minimize other complications of myeloma.
Thalidomide also has been used with effic successfully in the treatment of multiple myeloma.2 Although the mechanism of action is unclear (though may be related to a reduction in bone microvessel density or as a cytokine antagonist), thalidomide has been reported to yield a 40% to 50% response rate in patients with refractory disease. The most common toxicities of the agent are sedation and constipation. Thalidomide is contraindicated in pregnancy because it is highly teratogenic.