Multiple myeloma may also cause disruption in normal kidney health and function. It does this by producing harmful proteins that result in kidney damage. Hypercalcemia (excess calcium in the blood) caused by multiple myeloma also contributes to kidney damage. Hypercalcemia happens because of the rapid breakdown of bone tissue and results in excessive thirst, frequent urination, dehydration, and etc. 
It is hard to spot kidney problems until kidney function has significantly reduced, but you may experience fatigue, shortness of breath, itching, or edema in the legs in addition to hypercalcemia symptoms.  These symptoms should be reported to your doctor as they may indicate kidney problems.