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.
It may give rise to paraplegia in late-presenting cases.When the disease is well-controlled, neurological symptoms may result from current treatments, some of which may cause peripheral neuropathy, manifesting itself as numbness or pain in the hands, feet, and lower legs. Mouth
The initial symptoms may involve pain, numbness, swelling, expansion of the jaw, tooth mobility, and radiolucency. Multiple myeloma in the mouth can mimic common teeth problems like periapical abscess or periodontal abscess, gingivitis, periodontitis, or other gingival enlargement or masses. Cause
The cause of multiple myeloma is generally unknown. Risk factors
Monoclonal gammopathy of undetermined significance (MGUS) increases the risk of developing multiple myeloma. MGUS transforms to multiple myeloma at the rate of 1% to 2% per year, and almost all cases of multiple myeloma are preceded by MGUS. Smoldering multiple myeloma increases the risk of developing multiple myeloma. Individuals diagnosed with this premalignant disorder develop multiple myeloma at a rate of 10% per year for the first 5 years, 3% per year for the next 5 years, and then 1% per year. Obesity is related to multiple myeloma with each increase of body mass index by five increasing the risk by 11%.Studies have reported a familial predisposition to myeloma. Hyperphosphorylation of a number of proteins—the paratarg proteins—a tendency that is inherited in an autosomal dominant manner, appears a common mechanism in these families. This tendency is more common in African-American with myeloma and may contribute to the higher rates of myeloma in this group.