A 50 year old male patient complains of pain in back and legs. On routine investigations, it is found that he is anemic and his ESR is also raised. Which of the following is the most probable diagnosis for this patient?
Clinical findings stem mainly from:

The effects of plasma cells on the skeleton.
The production of excessive immunoglobulins, which often have abnormal physicochemical properties.
The suppression of humoral immunity.

Bone resorption often leads to pathologic fractures and chronic pain. The attendant hypercalcemia can give rise to neurologic manifestations, such as confusion, weakness, and lethargy, and contributes to renal dysfunction. Decreased production of normal immunoglobulins sets the stage for recurrent bacterial infections. Of great significance is renal insufficiency, which trails only infections as a cause of death.
Sickle cell anemia
Polycythemia
Waldenstrom macroglobulinemia
Multiple myeloma