Osteomalacia

Question 1

Definition

Answer 1

Osteomalacia is a disorder of mineralisation of bone matrix (osteoid)
It creates softening of the bone and is most commonly caused by severe vitamin D deficiency

o Rickets is a disorder of defective mineralisation of cartilage in the epiphyseal growth plates of children

Question 2

Risk factors of vitamin D deficiency

Answer 2

o Lack of exposure to sunlight
o Dietary deficiency
o Malabsorption
o Decreased 25-hydroxylation of vitamin D (due to liver disease, anticonvulsants)
o Decrease 1a-hydroxylation of vitamin D (due to chronic kidney disease, hypoparathyroidism)
o Vitamin D resistance

Question 3

Aetiology

Answer 3

Commonly caused by severe vitamin D deficiency

· Renal Phosphate Wasting

o Fanconi’s syndrome - characterised by:
· Phosphaturia
· Glycosuria
· Amino aciduria

o Renal tubular acidosis (type 2)

o Hereditary hypophosphataemic rickets (X-linked or autosomal dominant)

o Tumour induced osteomalacia

Question 4

Epidemiology

Answer 4

· COMMON in industrialised countries

· More common in FEMALES

Question 5

Presenting symptoms (osteomalacia)

Answer 5

o Bone pain (mainly in the axial skeleton)

o Weakness

o Malaise

Question 6

Presenting symptoms (rickets)

Answer 6

o Hypotonia

o Growth retardation

o Skeletal deformities

Question 7

Signs on physical examination (osteomalacia)

Answer 7

o Bone tenderness

o Proximal muscle weakness

o Waddling gait

o Signs of hypocalcaemia:
· Trousseau’s sign - inflation of a blood pressure cuff to above the systolic pressure for > 3 mins causes tetanic spasm of the wrist and fingers
· Chvostek’s sign - tapping over the facial nerve causes twitching of the ipsilateral facial muscles

Question 8

Signs on physical examination (rickets)

Answer 8

o Bossing of frontal and parietal bones

o Swelling of costochondral junctions (rickety rosary)

o Bow legs in early childhood

o ‘Knock knees’ in later childhood

o Short stature

Question 9

Investigations (bloods)

Answer 9

o Low or normal Ca2+
o Low phosphate
o High ALP
o Low 25-hydroxy vitamin D
o High PTH (secondary hyperparathyroidism)
o Check U&Es
o Check ABGs (for renal tubular acidosis)
o Increased phosphate excreting (in renal phosphate wasting)

Question 10

Investigations (radiographs)

Answer 10

o May appear normal

o May show osteopaenia

o Looser’s zones = wide, transverse lucencies traversing part way through a bone, usually at right angles to the involved cortex and are associated most frequently with osteomalacia and rickets (AKA pseudofractures)

Question 11

Investigations (bone biopsy)

Answer 11

· Bone biopsy after double tetracycline labelling

o Tetracycline is deposited at the mineralisation front as a band

o After two course of tetracycline (separated by a few days), the distance between the bands of deposited tetracycline is reduced in osteomalacia

o Not usually necessary for the diagnosis of osteomalacia

Question 12

Management plan

Answer 12

· Vitamin D and calcium replacement

· Monitor 24 hr urinary calcium

· Also monitor:
o Serum calcium
o Phosphate
o ALP
o PTH
o Vitamin D

· Treat the underlying CAUSE

Question 13

Possible complications

Answer 13

· Bone deformities

· Hypocalcaemia can cause epileptic seizures

· Cardiac arrhythmias

· Hypocalcaemic tetany

· Depression

· Hypocalcaemia symptoms = CATs go NUMB
o Convulsions
o Arrhythmias
o Tetany
o NUMBness/paraesthesia

Question 14

Prognosis

Answer 14

· Symptoms and radiological appearances improve with vitamin D treatment

· Bone deformities in children tend to be permanent