Osteomalacia — SCE Rheumatology MCQ

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ModerateMetabolic Bone DiseaseOsteomalaciaSCE Rheumatology

A 65-year-old woman with coeliac disease and persistent diarrhoea sustains a vertebral crush fracture. Her adjusted serum calcium is 1.95 mmol/L, phosphate 0.60 mmol/L and alkaline phosphatase 350 U/L; the remainder of her liver biochemical tests are normal. Her serum 25-hydroxyvitamin D concentration is 15 nmol/L. Which diagnosis best explains the fracture and biochemical abnormalities?

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Correct answer: D — Vitamin D-deficiency osteomalacia

The correct answer is vitamin D-deficiency osteomalacia. Persistent diarrhoea from coeliac disease causes malabsorption of vitamin D and calcium. Severe vitamin D deficiency reduces intestinal calcium and phosphate availability, with secondary hyperparathyroidism contributing to phosphate loss. The resulting low calcium, low phosphate and raised alkaline phosphatase indicate defective mineralisation of osteoid and explain the fragility fracture. Primary hyperparathyroidism usually causes hypercalcaemia rather than hypocalcaemia. Paget disease can markedly increase alkaline phosphatase, but calcium and phosphate are generally normal and the profound vitamin D deficiency remains unexplained. Skeletal metastases do not characteristically produce this coherent malabsorptive biochemical pattern. Postmenopausal osteoporosis causes reduced bone mass with normally mineralised bone and usually normal calcium, phosphate and alkaline phosphatase.

Reference: Minisola S, et al. Osteomalacia and Vitamin D Status: A Clinical Update 2020. JBMR Plus. 2021;5:e10447. https://pubmed.ncbi.nlm.nih.gov/33553992/