Makindo Medical Notes

💡 Phosphate binds to calcium — both are essential for mineralisation, alongside vitamin D, to form strong bones and teeth. Failure of this system → soft, poorly mineralised bone (rickets in children, osteomalacia in adults).

📖 About

• Osteomalacia: defective mineralisation of mature bone matrix (osteoid) after epiphyseal closure → soft, painful bones.
• Rickets: defective mineralisation at the growth plate in children → skeletal deformity, growth failure.
• Both conditions → weak, painful bones, poor growth, ↑ fracture risk.

⚙️ Aetiology

• Vitamin D deficiency: diet (low dairy/oily fish/eggs), lack of sunlight, skin covering.
• Malabsorption: coeliac disease, Crohn’s, CF, gastrectomy, PBC.
• Renal causes: chronic kidney disease (↓ 1α-hydroxylation), renal phosphate wasting (Fanconi syndrome, RTA II, X-linked hypophosphataemia).
• Hepatic disease: impaired 25-hydroxylation (cirrhosis, chronic liver disease).
• Drugs: anticonvulsants (phenytoin, carbamazepine), rifampicin, antiretrovirals → ↑ vitamin D breakdown.
• Tumour-induced osteomalacia: excess FGF-23 → renal phosphate wasting, myalgia, weakness.
• Inherited forms: vitamin D–dependent rickets (receptor or hydroxylase mutations), X-linked hypophosphataemia.
• Risk factors: dark skin, pregnancy, breastfeeding, elderly, little sun exposure.

🔬 Pathology

• Rickets: poor mineralisation of epiphyseal cartilage → widened, irregular growth plates, deformity.
• Osteomalacia: unmineralised osteoid accumulates → fragile, painful bones.

📜 History

• 1645: Daniel Whistler first described “the English disease” (rickets).
• Osteomalacia: from Greek osteo- (bone) + malakia (softness).

🧬 Clinical Features

• Rickets (children): growth retardation, hypotonia, apathy, short stature, dental enamel defects.
• Skeletal signs:
  • “Rickety rosary” = bead-like costochondral junctions.
  • Harrison’s sulcus = chest wall indentation.
  • Craniotabes (soft skull), frontal bossing.
  • Bowed legs, knock knees once weight bearing.
• Osteomalacia (adults): proximal myopathy, bone pain, tenderness (esp. sternum, tibiae, pelvis).
• Waddling gait, difficulty rising from chair (low phosphate, proximal weakness).
• Fragile bones, stress fractures, Looser’s zones (pseudofractures).
• Hypocalcaemic tetany possible.

🆚 Differentials (adults)

• Osteoporosis: reduced bone mass but normal mineralisation.
• Paget’s disease: disorganised bone remodelling.
• Congenital syphilis (children): bone deformity mimicking rickets.

🧪 Investigations

• ↓ calcium, ↓ phosphate, ↑ alkaline phosphatase (90%).
• ↑ PTH (secondary hyperparathyroidism from low Ca²⁺).
• ↓ serum 25(OH)D3 (<25 nmol/L diagnostic of deficiency).
• ↑ FGF-23 in tumour-induced osteomalacia (causes phosphate loss).
• VBG: hyperchloraemic metabolic acidosis (proximal RTA).
• X-rays: Looser’s zones = classic pseudofractures (pubic rami, femoral neck, humeral neck, scapular borders).
• Bone biopsy: rarely needed, shows increased unmineralised osteoid.

🛡 Prevention

• Pregnant & breastfeeding women: 10 mcg/day vitamin D supplement (Oct–Mar in UK).
• Infants <1 year: 8.5–10 mcg/day unless on ≥500 ml formula (fortified).
• Children 1–4 years: 10 mcg/day supplement.
• Adults: encourage safe sunlight, balanced diet with dairy, oily fish, fortified foods.

💊 Management

• Diet: adequate calcium, phosphate, vitamin D, plus sunlight.
• Vitamin D replacement:
  • Ergocalciferol/cholecalciferol (D2/D3) 50,000 units weekly × 6–12 weeks PO, or 300,000 units IM × 2 doses.
  • Maintenance: 800–1000 IU/day PO long-term.
• Calcium: 1000–1200 mg/day if dietary intake inadequate.
• Renal/liver disease: use active forms (alfacalcidol, calcitriol) with careful Ca²⁺ monitoring (risk of hypercalcaemia).
• Tumour-induced osteomalacia: treat underlying tumour.
• X-linked hypophosphataemia: oral phosphate + calcitriol/alfacalcidol.

📌 OSCE / Exam Pearls

• Think rickets if child with bowed legs, widened wrists, “rickety rosary.”
• Looser’s zones = incomplete stress fractures pathognomonic of osteomalacia.
• Biochemistry triad: ↓ Ca²⁺, ↓ PO₄³⁻, ↑ ALP.
• Differentiate from osteoporosis: mineralisation is defective in osteomalacia, normal in osteoporosis.

📚 References

• Nottingham APC: Vitamin D Guidelines
• NHS: Rickets & Osteomalacia
• Kumar & Clark’s Clinical Medicine, 10th edition.

🧾 Clinical Case Examples – Rickets & Osteomalacia

Case 1 – Rickets in a Child 👶 A 3-year-old boy of Somali origin is brought to clinic with bowed legs and delayed walking. His diet is low in dairy, and he spends most of his time indoors. Exam: widened wrists, rachitic rosary at costochondral junctions, height below 5th centile. Bloods: Ca²⁺ low, phosphate low, ALP high, vitamin D 12 nmol/L. 👉 Diagnosis: Nutritional rickets. 👉 Management: Vitamin D supplementation, dietary advice, encourage safe sunlight exposure.

Case 2 – Osteomalacia in an Adult 🌙 A 45-year-old woman presents with diffuse bone pain, proximal muscle weakness, and difficulty rising from a chair. She wears a full-body covering outdoors and avoids sunlight. Exam: waddling gait, bone tenderness over sternum and tibiae. X-ray: Looser’s zones (pseudofractures). Bloods: Ca²⁺ low, phosphate low, ALP high, vitamin D 18 nmol/L. 👉 Diagnosis: Osteomalacia due to vitamin D deficiency. 👉 Management: High-dose vitamin D loading (50,000 IU weekly × 8 weeks), maintenance 1000 IU/day, calcium supplementation if dietary intake inadequate.