This patient should undergo MRI of the lumbar spine. He has a diagnosis of smoldering (asymptomatic) multiple myeloma, which is defined as an M protein level of 3 g/dL or more or clonal plasma cells representing 10% or more of the total marrow cellularity on bone marrow biopsy but the absence of disease-specific signs or symptoms. Most patients with smoldering myeloma eventually develop symptomatic disease, with a median time to progression of 4.8 years. Therefore, surveillance in these patients is necessary. The CRAB (hyperCalcemia, Renal failure, Anemia, Bone disease) criteria for a diagnosis of multiple myeloma requiring therapy are commonly used to determine the need to start chemotherapy. Although this patient does not have hypercalcemia, kidney disease (renal failure), or anemia, he is experiencing unexplained lower back pain with nonspecific findings on plain radiographic imaging. Therefore, additional imaging is warranted to better determine the cause of the pain. Although plain radiography remains an important component of the initial evaluation of patients with multiple myeloma, more than 30% of trabecular bone must be lost before lytic lesions are evident by plain radiographs. MRI is a more sensitive imaging modality for detecting lytic bone lesions of myeloma, and would be the preferred next imaging study in this patient. Additional imaging techniques that may be used in multiple myeloma include CT or PET/CT.

The role of chemotherapy in patients with smoldering myeloma is unclear. Although lenalidomide and dexamethasone have been shown to delay disease progression, the optimal patient population for these agents has not been identified, and early initiation of chemotherapy for smoldering myeloma is not routinely utilized.

Although most patients with acute low-back pain may be treated conservatively without imaging, symptomatic treatment of this patient's low back pain with routine follow-up would not be appropriate because of his diagnosis of multiple myeloma and the possibility that his back pain is secondary to disease progression.

Bisphosphonates are a key component of therapy for patients with multiple myeloma requiring therapy. Zoledronic acid has been shown to reduce the risk of skeletal-related events and improve progression-free survival. However, the patient has yet to be diagnosed with symptomatic myeloma. No role exists for the routine use of bisphosphonates for patients with smoldering myeloma.