Hypophosphatasia — SCE Rheumatology MCQ

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ModerateMetabolic Bone DiseaseHypophosphatasiaSCE Rheumatology

A 48-year-old woman has recurrent metatarsal stress fractures, premature loss of adult teeth and chronic musculoskeletal pain. ALP is repeatedly low, calcium and PTH are normal, and vitamin D is adequate. DEXA shows osteopenia. What is the most likely diagnosis?

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Correct answer: E — Hypophosphatasia

Explanation lettering: D = shown as C · E = shown as D · C = shown as E

Hypophosphatasia is best because recurrent fractures with dental loss and persistently low ALP suggest adult hypophosphatasia. A is less suitable because primary hyperparathyroidism causes high calcium and PTH; B is less suitable because myeloma would be suggested by paraprotein, anaemia or lytic lesions; D is less suitable because Paget disease causes high ALP; E is less suitable because vitamin D osteomalacia usually raises ALP. Clinical pearl: low ALP is a diagnostic clue, not a normal variant, in recurrent fracture presentations.

Reference: Oxford Textbook of Rheumatology