Description

• Multiple myeloma (MM) is a malignant proliferation of a single clone of plasma cells. These malignant cells produce monoclonal protein (immunoglobulin [Ig]) that can be detected in the blood and/or urine as it is filtered in the kidneys.
• MM is characterized by bony lytic lesions, hypercalcemia, increased susceptibility to infections, and renal impairment.
• Monoclonal gammopathy of undetermined significance (MGUS) is a common disorder with limited monoclonal plasma cell proliferation that can progress to smoldering MM (SMM) or symptomatic MM at rate of ~1% per year.

Epidemiology

• MM affects the older adults with a median age of 65 to 74 years.
• Accounts for nearly 2% of all cancers and 17% of hematologic malignancies in the United States
• African Americans about 2 to 3 times more commonly affected than Caucasians; less common in Asians

Incidence
7 cases per 100,000 in the United States annually

Prevalence
In 2018, there were ~160,000 recognized cases worldwide.

Etiology and Pathophysiology

• It is most likely caused by genetic alteration involving chromosomal abnormalities and sporadic mutations.
• Genetic damage in developing B lymphocytes occur at time of isotype switching.
• Chromosomal abnormalities involve Ig heavy chain translocations, with cyclin D1 t(11;14) the most common, and deletion of 17p13 (p53 locus).

Genetics
MM rarely occurs in familial clusters. A rare form of paratarg-7 protein might have pathogenic role.

Risk Factors

• Most cases have no known risks associated.
• Old age; immunosuppression; and exposure to chemicals, heavy metals, and ionizing radiation increase the risk of MM.

Commonly Associated Conditions

Secondary amyloidosis can be associated with MM and polyneuropathy, organomegaly, endocrinopathy, M protein, skin changes (POEMS)