Victoria Harraway

Department of Chemical Pathology, Pathology Queensland, Qld, Australia

A 58 year old male presented to the Emergency Department with worsening back pain, following a suspected mechanical injury three weeks prior. He had no past medical history but did report recent poor appetite and 15kg of unintentional weight loss. 

A CT spine showed an acute pathological compression fracture of L2, and heterogenous marrow. Laboratory investigations included a full blood count, which showed normocytic anaemia (Hb 111g/L), and serum chemistry which showed a critically elevated calcium level (4.31 mmol/L, corrected calcium 4.67 mmol/L) and elevated globulin (95g/L). Ionised calcium on the paired blood gas was noted to be normal (1.28 mmol/L).

Serum protein electrophoresis revealed an IgG kappa paraprotein. The patient underwent bone marrow testing and was diagnosed with multiple myeloma. 

Hypercalcaemia is common in multiple myeloma and is used for diagnostic purposes. It is, however, important to note that several cases of pseudohypercalcaemia in multiple myeloma have been reported. Pseudohypercalcaemia occurs due to the binding of calcium by monoclonal immunoglobulins, resulting in an elevation of total serum calcium, with ionised calcium remaining normal. 

This case highlights the importance of ionised calcium measurement in patients with monoclonal gammopathies and multiple myeloma, to prevent erroneous treatment and misclassification of disease.