MGUS is a relatively stable condition afflicting 3% of people aged 50 and 5% of people aged 70; it progresses to multiple myeloma at a rate of 0.5–1% cases per year; smoldering multiple myeloma does so at a rate of 10% per year for the first 5 years, but then falls off sharply to 3% per year for the next 5 years and thereafter to 1% per year.Overall, some 2–4% of multiple myeloma cases eventually progress to plasma cell leukemia. Diagnosis
Blood tests
The globulin level may be normal in established disease. A doctor may request protein electrophoresis of the blood and urine, which might show the presence of a paraprotein (monoclonal protein, or M protein) band, with or without reduction of the other (normal) immunoglobulins (known as immune paresis). One type of paraprotein is the Bence Jones protein, which is a urinary paraprotein composed of free light chains. Quantitative measurements of the paraprotein are necessary to establish a diagnosis and to monitor the disease. The paraprotein is an abnormal immunoglobulin produced by the tumor clone. In theory, multiple myeloma can produce all classes of immunoglobulin, but IgG paraproteins are most common, followed by IgA and IgM. IgD and IgE myeloma are very rare. In addition, light and or heavy chains (the building blocks of antibodies) may be secreted in isolation: κ- or λ-light chains or any of the five types of heavy chains (α-, γ-, δ-, ε- or μ-heavy chains).
People with amyloidosis have high levels of amyloid protein that can be excreted through the kidneys and cause damage to the kidneys and other organs.Light chains produce myriad effects that can manifest as the Fanconi syndrome (type II kidney tubular acidosis). Infection
The most common infections are pneumonias and pyelonephritis. Common pneumonia pathogens include S. pneumoniae, S. aureus, and K. pneumoniae, while common pathogens causing pyelonephritis include E. coli and other Gram-negative organisms. The greatest risk period for the occurrence of infection is in the initial few months after the start of chemotherapy. The increased risk of infection is due to immune deficiency. Although the total immunoglobulin level is typically elevated in multiple myeloma, the majority of the antibodies are ineffective monoclonal antibodies from the clonal plasma cell. A selected group of people with documented hypogammaglobulinemia may benefit from replacement immunoglobulin therapy to reduce the risk of infection. Neurological symptoms
Some symptoms (e.g., weakness, confusion, and fatigue) may be due to anemia or hypercalcemia. Headache, visual changes, and retinopathy may be the result of hyperviscosity  of the blood depending on the properties of the paraprotein. Finally, radicular pain, loss of bowel or bladder control (due to involvement of spinal cord leading to cord compression) or carpal tunnel syndrome, and other neuropathies (due to infiltration of peripheral nerves by amyloid) may occur.