Disease Mechanism
Plasma cells normally produce cytokines which stimulate the growth of osteoclasts. When there are too many plasma cells, the excess number of osteoclasts lead to bone dissolution. When more than 30% of a bone has dissolved, osteoporosis will occur and a dark lesion that looks like a hole may appear in the bone. These holes weaken the bone, increasing the potential for fractures, and can cause severe pain.
As the osteoclasts resorb the bone, calcium is released and serum calcium levels rise. The resultant hypercalcemia may affect kidney function.
Plasma cells normally produce proteins called antibodies. Too many proteins caused by the proliferation of plasma cells from multiple myeloma can cause a condition called hyperviscosity, which thickens the blood, resulting in bleeding of the nose or gums, and increasing the risk of a stroke. Increased proteins and calcium in the urine can lead to kidney failure.
The elevated numbers of plasma cells seen in multiple myeloma physically reduce the number of red and white blood cells, resulting in anemia and weakening the immune system. This leaves the patient susceptible to infection.