Correction

Due to a publication error, the legend text that accompanied the cover image on Volume 12, Issue 4 (April 2017) was incorrect. The correct legend text appears below:

What’s the Diagnosis?

A 37-year-old man with IgA glomerulonephritis developed hyperparathyroidism with hypercalcemia and underwent subtotal parathyroidectomy in 2003, with a single parathyroid gland left in situ. He received a kidney transplant in 2005, and due to recurrent hyperparathyroidism and hypercalcemia, he was treated with zoledronic acid. In 2009, the transplant failed and he returned to hemodialysis and commenced cinacalcet. He also required left hip replacement for avascular necrosis.

In 2016, because of persisting hyperparathyroidism with an intact PTH of 126 pmol/L (1184 pg/ml), bone specific alkaline phosphatase of 73.3 μg/L, and poor phosphate control, he was referred for a bone mineral density by dual-energy X-ray absorptiometry (DXA) as part of the workup for a possible repeat neck exploration and parathyroidectomy. The lumbar spine T-scores were elevated: the L1 T-score was 3.2, L2 9.4, L3 7.9, and L4 was 3.5 (left image). His nephrologist was contacted regarding the high bone mineral density (BMD) and ordered a plain X-ray of the abdomen (right image).

BMD by DXA is an areal measure, and vascular or ligamentous calcification, degenerative changes, or compression fractures may cause BMD overestimation. However, this patient was taking lanthanum carbonate as his phosphate binder. Lanthanum (derived from the Greek word for “hidden”) has a density of 6.16 g/cm³, almost twice that of barium, and is radiodense on abdominal X-ray. When lanthanum in the bowel lumen overlies the spine, it dramatically increases lumbar spine BMD and would be expected to make the spinal and hip BMD discordant (1). Paradoxically, if lanthanum only overlies soft tissues beside the spine, it might reduce the calculated BMD by DXA (2).

Figure 1.

Patients treated with lanthanum carbonate generally take the drug with each meal, so some lanthanum will inevitably be present in the bowel if patients are compliant. Nevertheless, the effect of lanthanum on BMD in patients on dialysis has not been considered by most investigators. When patients are on treatment with lanthanum carbonate, lumbar spine BMD values should be interpreted cautiously, and the results of some bone density studies may need re-evaluation.

(Cover image and text provided by Grahame J. Elder, Westmead Hospital - Department of Renal Medicine, Westmead, New South Wales, Australia, and the Garvan Institute of Medical Research - Osteoporosis and Bone Biology Program, Darlinghurst, New South Wales, Australia; and Eric Hoi Kit Au, Westmead Hospital - Department of Renal Medicine, Westmead, New South Wales, Australia)