AKT · Musculoskeletal/Metabolic bone & tumourslow yield

Osteomalacia & rickets

Defective mineralisation of osteoid (vitamin D deficiency) — rickets in growing bone

Overview

Defective mineralisation of bone matrix, usually from vitamin D deficiency (also renal disease, hypophosphataemia). In adults it is osteomalacia (bone pain, proximal weakness, fractures); in children with open growth plates it is rickets (bowed legs, swollen joints, growth failure). The biochemistry — low/normal calcium and phosphate with HIGH ALP — distinguishes it from osteoporosis (normal biochemistry).

Recognise

Osteomalacia: diffuse bone pain/tenderness, proximal myopathy (waddling gait), fragility fractures, Looser zones (pseudofractures) on X-ray
Rickets: bowing of the legs (genu varum), swelling of the wrists/costochondral junctions (rachitic rosary), delayed growth/fontanelle closure, hypotonia
Biochemistry: low/normal calcium & phosphate, HIGH alkaline phosphatase, low vitamin D, raised PTH (secondary hyperparathyroidism)

Red flags

Symptomatic hypocalcaemia (tetany, seizures, prolonged QT) → calcium replacement
Rule out renal osteodystrophy (CKD) and hypophosphataemic (X-linked) rickets if not responding to vitamin D

Differentials & how to tell them apart

OsteoporosisNORMAL calcium/phosphate/ALP — reduced bone mass, no mineralisation defect

Hypophosphataemic (X-linked) ricketslow phosphate, normal vitamin D, doesn't respond to vitamin D alone

Renal osteodystrophyCKD with high phosphate, low calcium, high PTH

Paget's diseasevery high ALP but normal calcium/phosphate and characteristic X-ray

Investigations

Vitamin D (25-OH, low), calcium and phosphate (low/normal), ALP (HIGH), PTH (raised), U&Es (renal cause); X-ray (Looser zones in osteomalacia; cupped/frayed metaphyses in rickets); distinguish from osteoporosis (normal biochemistry).

Management

Vitamin D (± calcium) replacement; treat the underlying cause

1Recognise the biochemistry (low vitamin D, low/normal Ca/PO4, HIGH ALP, raised PTH). Replace vitamin D (colecalciferol) with calcium as needed; investigate the cause (diet/sunlight, malabsorption, renal).Gate: Distinguish from osteoporosis (which has NORMAL biochemistry); non-response to vitamin D suggests renal osteodystrophy or hypophosphataemic rickets needing active vitamin D/phosphate.
2Treat the underlying cause — active vitamin D (alfacalcidol) for renal disease, phosphate for hypophosphataemic rickets, and manage malabsorption (e.g. coeliac).

Vitamin D replacement (colecalciferol) — first-line — loading then maintenance; corrects the deficiency

Calcium supplementation — if dietary intake low or to correct hypocalcaemia

Treat the underlying cause — phosphate/active vitamin D (alfacalcidol) for renal disease; phosphate ± calcitriol for hypophosphataemic rickets

Address malabsorption/diet/sunlight — coeliac disease, limited sun exposure

Key points

Bone pain + proximal myopathy + HIGH ALP with low/normal calcium & phosphate and low vitamin D = osteomalacia (rickets in children: bowed legs, rachitic rosary). Vitamin D ± calcium. The biochemistry separates it from osteoporosis (normal). Looser zones on X-ray.

Monitor & prognosis

Vitamin D/calcium/PTH/ALP normalisation, symptom and X-ray resolution.

Excellent with vitamin D replacement; deformities in established rickets may persist.

Source: NICE CKS (vitamin D deficiency); cross-ref endocrine (bone profile)