Multiple myeloma (MM), a hematologic malignancy characterized by monoclonal proliferation of mature plasma cells, accounts for 10% of all hematological conditions, and is the most common primary osseous malignancy in the elderly population, with a slight male predominance. It is a severe disease, and overall the prognosis is poor, with a 5-year survival rate of about 35%.

MM must be differentiated from other clonal neoplasms that may resemble it, with which it shares some features:  MGUS (Monoclonal Gammopathy of Undetermined Significance), Smoldering multiple myeloma (SMM) and plasmacytomas. 

MGUS (Monoclonal Gammopathy of Undetermined Significance) is a benign condition in which a paraprotein is found  at a concentration of < 3g/dL in an asymptomatic patient. It resembles Multiple Myeloma, but with a lower concentration of antibodies and fewer plasma cells, and it is a benign entity that requires no treatment. However, MGUS has the risk of transforming to Multiple Myeloma at a rate of 1.5% per year, so monitoring is recommended. 

Smoldering multiple myeloma (SMM) is an asymptomatic clonal plasma cell disorder. SMM is distinguished from MGUS by a much higher risk of progression to multiple myeloma (MM). Studies show that some patients with SMM can benefit from early therapy, so currently there is a need to accurately diagnose and risk-stratify patients with SMM.

Plasmacytomas are plasma cell neoplasms without evidence of systemic disease (normocalcemia, absence of anemia, preservation of uninvolved immunoglobulins, or renal disease attributable to myeloma).They represent less than 5% of patients with a plasma cell dyscrasia. Plasmacytomas  can be subdivided in single bone (SBP) or extramedullary plasmacytomas (EMP) Diagnosis requires biopsy confirmation of a monoclonal plasma cell infiltrate from a single site. The majority of patients with solitary plasmacytoma of bone develop myeloma after a median of 2-3 years, but the overall median survival of 7-12 years is longer than for patients in early phases of symptomatic myieloma

The main features of the Multiple Myeloma are represented by the "CRAB" acronym:

C: Calcium. Hypercalcemia

R: Renal. Renal insufficiency.

A: Anemia. Anemia is the most common presenting sign, with or without the pressence of symptoms like bone pain, fatigue or weight loss.

B: Bone disease. Bone disease is the most frequent feature of multiple myeloma, occurring in approximately two-thirds of patients at diagnosis and in nearly all patients during the course of their disease. 

Imaging techniques are fundamental in the identification of bone disease, but their role goes far beyond the mere identification of lesions.

Fig. 2: The role of imaging techniques in Multiple myeloma

Since we are dealing with a predominantly diffuse disease, we need to explore all the skeletal system in the same study.