Endocrine Abstracts

We present the case of 63 years old female patient who was diagnosed with IG G kappa multiple myeloma in 2007. Cytogenetics investigations revealed high risk for progression of the disease (cytogenetics: 17 p deletion and t (4/14). The patient decided against active treatment. Over 10 years she was kept under observation with no symptoms. Her basal paraprotein levels slowly progressed from 14 g/l up to 18 g/l. In 2017 she developed mild hypercalcaemia (corrected calcium 2.72 mmol/l) and imaging investigations revealed focal myeloma bone deposits with no activity on FDG PET scan. During the following two years the patient remained asymptomatic. Calcium levels continued to rise (peak corrected calcium up to 3.2 mmol/l) despite treatment with bisphosphonate infusion (4 mg Zoledronic acid). Paraprotein levels increased up to 43 g/l. Inappropriately normal PTH levels, prompted further investigations in order to exclude concomitant hyperparathyroidism. Bone density scan revealed normal bone mass, bone markers showed normal metabolic bone activity (CTX 0.37, PNP1 58). Imaging investigations showed no topical parathyroid disease. We considered the differential diagnosis of pseudo-hypercalcaemia related to high levels of abnormal paraproteins. A simple venous blood gas test revealed normal ionised calcium of 1.20 (NR <1.3) which supported the hypothesis. Subsequent drop in PTH levels down to 2.8 pmol/l (NR >1.6) is likely to represent a response to variation in serum calcium levels within the reference range. Multiple myeloma bone disease in 90% of patients presents with symptomatic osteolytic bone disease. Treatment with bisphosphonates is essential to suppress cytokine induced activation of RANKL/OPG system and to correct hypercalcaemia. Disease control remains the major element in treatment of myeloma bone disease. Simple biochemical markers could support clinicians in their differential diagnostic reasonings and guide further therapeutic management. Pseudo-hypercalcaemia due to high paraprotein levels should be considered in the differential diagnosis of hypercalcaemia in multiple myeloma in asymptomatic patients to avoid unnecessary investigations and interventions.