A Rare Case of Nonsecretory Multiple Myeloma: Pitfall of Hypercalcemia

Introduction: Hypercalcemia is a common disorder normally caused by primary hyperparathyroidism or malignancy. Basically some disease signals seem to come out on the process of differential diagnosis. However, non-secretory multiple myeloma (NSMM) is a rare case and might not show any signs and lead us hard to diagnose it. Case Description: An 80-year-old man was urgently admitted to our hospital with lower back pain, appetite loss and progressed his limitation of movement and weakness. He had type 2 diabetes and hypertension in his past history. The laboratory data just showed acute kidney injury(serum creatinin 1.63mg/dl) with hypercacemia(serum calcium 1.32mg/dl, calcium ion 1.61mmol/L ), moderate higher CRP(5.59mg/dl), hyperuricemia (13.2mg/dl) and metabolic alkalosis. Computed tomography was not detected any abnormality. Both of Urinary BJP and M protein was negative. On Day 21, we rechecked abdominal CT and it showed newly osteolytic lesion on the left ischium. Bone marrow aspiration revealed eventually malignant myeloma and non-producer and non-secretory myeloma cells with both negative findings of M protein and deviation of free light chains. Discussion: We experienced a rare case of NSMM with acute kidney injury and hypercalcemia. We struggled about differential diagnosis of hypercalcemia without M peak in serum and urinary Bence Jones protein (BJP). Only osteolytic lesions in the lumbar, appeared in three weeks after admission, led us to diagnosis of multiple myeloma. We should seek the examination of bone marrow aspiration and smear of peripheral blood if we get nothing of causes in regard to hypercalcemia.