Back pain in the older population is most often attributed to the degenerative process. However, other, more ominous, processes can often cause back pain. One of these conditions, which is often overlooked and often results in a delay in diagnosis, is multiple myeloma, a malignant proliferation of plasma cells. In 10% of patients with multiple myeloma, the course is indolent, occurring over years. The cause is not known. The median age is 68, and it is uncommon below the age of 40. It occurs in approximately four per 100,000 patients. Males are more often affected than females, and African-Americans are more at risk than Caucasians by two to one.
Back pain is the most common symptom, presenting in approximately 70% of patients. It occurs less often at night and is more often associated with activity, which differs from metastatic disease of the spine. Persistent, localized, severe pain is usually associated with a spinal fracture. Other symptoms are related to the abnormal plasma cell protein metabolism and hypercalcemia from bone resorption, which can lead to renal dysfunction, anemia and neurologic abnormalities.
Proliferation of these malignant plasma cells occurs primarily in the bone and bone marrow. Palpable lesions may be present in the skull, clavicle or sternum. Bone lesions appear as holes in the bone with no new bone formation due to the activation of osteoclasts and the suppression of osteoblasts, the result of osteoclastic-stimulating factors produced from the myeloma cells. Since osteoblasts are suppressed, radioisotope bone scanning is less useful. MRI is a more valuable tool to evaluate the marrow replacement process. Regular X-ray imaging still remains an excellent tool in the later stages but may be less reliable in the early stages.
Additional workup in the initial evaluation is directed toward identifying the presence of abnormal plasma cell proteins, an abnormal metabolic state and a malignant process by obtaining a complete blood count, sedimentation rate, serum protein electrophoresis, 24-hour urine test for Bence Jones proteins and metabolic and renal function studies. Treatment, directed by an oncologist, usually consists of chemotherapy, but a bone marrow transplant or the use of radiation may be indicated. Surgical management is usually reserved for stabilization procedures in the presence of spinal instability.
MD News November 2009