Medical Emergencies · patient case question
Which laboratory finding is characteristic of osteomalacia?
Patient case: The Hypothyroid Patient with an Aching Jaw
Patient: 54-year-old female
Chief Complaint: Generalized aching in the jaws and fatigue.
Background: Hashimoto thyroiditis diagnosed two years ago. Recently also investigated for bone pain; laboratory work shows a raised alkaline phosphatase with low vitamin D.
Medications: Levothyroxine
Vital Signs: BP 118/74 mmHg · HR 58 bpm · RR 14 · T 97.4°F
Findings: Dry cool skin, coarse hair, periorbital puffiness, slow relaxation of deep tendon reflexes. Intraorally the tongue is enlarged with scalloped margins. Panoramic film shows generalized reduced bone density.
Show answer and explanation
Correct answer: D. Elevated alkaline phosphatase
- A. Haemoglobin is unrelated to osteomalacia.
- B. Serum phosphate is typically LOW, from the phosphaturic effect of the raised PTH.
- C. Serum calcium is typically LOW or low-normal, which is what drives the compensatory rise in PTH.
- D. CORRECT. ELEVATED ALKALINE PHOSPHATASE is the hallmark. Osteomalacia is defective MINERALISATION of osteoid, usually from vitamin D deficiency. The osteoblasts remain active and continue laying down unmineralised matrix, and alkaline phosphatase — an osteoblast product — rises accordingly. The characteristic panel is: LOW or low-normal calcium, LOW phosphate, HIGH alkaline phosphatase, HIGH parathyroid hormone (secondary hyperparathyroidism) and LOW 25-hydroxyvitamin D.
Note: The parallel disorder in children is RICKETS, where the same defect affects the growth plate and produces bowing of the long bones, a rachitic rosary and delayed fontanelle closure. Dental features of both: enamel hypoplasia, delayed eruption, large pulp chambers with high pulp horns, and hypomineralised dentine.
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