Osteomalacia — SCE Rheumatology MCQ

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EasyMetabolic bone diseaseOsteomalaciaSCE Rheumatology

A 42-year-old woman who routinely wears concealing clothing presents with diffuse bone pain and proximal muscle weakness. Examination demonstrates a waddling gait. Her serum 25-hydroxyvitamin D concentration is very low, adjusted calcium is low-normal, phosphate is low and alkaline phosphatase is raised. What is the most likely diagnosis?

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Correct answer: C — Osteomalacia

The correct answer is C, osteomalacia due to severe vitamin D deficiency. Reduced sunlight exposure from concealing clothing is a relevant risk factor. Diffuse bone pain, proximal myopathy and a waddling gait are characteristic clinical features. Defective mineralisation produces a raised alkaline phosphatase; secondary hyperparathyroidism commonly leads to low phosphate, while calcium may remain low-normal before becoming frankly low. Osteoporosis is usually asymptomatic until fracture and does not produce this biochemical pattern. Paget disease can raise alkaline phosphatase but is usually focal, occurs in older adults and does not explain severe vitamin D deficiency with hypophosphataemia. Hypothyroid myopathy causes proximal weakness but not the characteristic bone pain and mineral abnormalities. Polymyalgia rheumatica is unusual below age 50 and does not cause this biochemical profile.

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