Vitamin D deficiency

Question 1

What parameter defines vitamin D deficiency?

Answer 1

<20ng/mL (levels should ideally be >30ng/mL)

Question 2

What 2 conditions arise from vitamin D deficiency?

Answer 2

Osteomalacia: disorder of mineralisation of bone matrix (osteoid)
Rickets: defective mineralisation of cartilage in the epiphyseal growth plates of children

Question 3

List risk factors for vitamin D deficiency

Answer 3

Lack of exposure to sunlight
Increased skin pigmentation
Ageing (ability of skin to produce vitD decreases with age)
Dietary deficiency
Malabsorption
Decreased 25-hydroxylation of vitamin D (liver disease, anticonvulsants)
Decrease 1a-hydroxylation of vitamin D (CKD, hypoparathyroidism)
Vitamin D resistance

Question 4

List risk factors for Renal Phosphate Wasting

Answer 4

Fanconi’s syndrome (XS glucose, bicarbonates, phosphates, aa + uric acid being excreted in the urine)
Renal tubular acidosis (type 2)
Hereditary hypophosphataemic rickets (X-linked or AD)
Tumour induced osteomalacia

Question 5

What is Fanconi’s syndrome characterised by?

Answer 5

Phosphaturia
Glycosuria
Amino aciduria

Question 6

Describe the epidemiology of vitamin D deficiency

Answer 6

COMMON in industrialised countries

F > M

Question 7

List 3 symptoms of osteomalacia

Answer 7

Bone pain (mainly in axial skeleton)
Weakness
Malaise

Question 8

List 4 symptoms of rickets

Answer 8

Hypotonia
Growth retardation
Skeletal deformities
Head sweating

Question 9

List 3 signs of osteomalacia

Answer 9

Bone tenderness
Proximal muscle weakness
Waddling gait

Question 10

List 6 signs of rickets

Answer 10

Bossing of frontal + parietal bones
Swelling of costochondral junctions (rickety rosary)
Bow legs -> ‘Knock knees’
Short stature
Delayed tooth eruption
Chest deformities e.g. pectus carinatum + thoracic asymmetry

Question 11

What signs of hypocalcaemia may be seen in vitamin D deficiency?

Answer 11

Trousseau’s sign: inflation of BP cuff to above the systolic pressure for > 3 mins causes tetanic spasm of the wrist + fingers
Chvostek’s sign: tapping over the facial nerve causes twitching of ipsilateral facial muscles

Question 12

What bloods should be investigated in vitamin D deficiency?

Answer 12

Low (if longstanding) or normal Ca2+ 
Low phosphate but usually norm  
High ALP  
Low 25-hydroxy vitamin D 
High PTH (secondary hyperparathyroidism) 
Check U+Es 
Check ABGs (for renal tubular acidosis) 
Increased phosphate excretion (renal phosphate wasting)

Question 13

What may be seen on radiographs in vitamin D deficiency?

Answer 13

May appear normal
May show osteopaenia
Looser’s zones

Question 14

What are Looser’s zones?

Answer 14

wide, transverse lucencies traversing part way through a bone, usually at right angles to the involved cortex (AKA pseudofractures)

Question 15

What may be seen on bone biopsy after double tetracycline labelling in osteomalacia?

Answer 15

Tetracycline is deposited at the mineralisation front as a band
After 2nd course of tetracycline (separated by a few days), distance between the bands of deposited tetracycline is reduced in osteomalacia
Not usually necessary for the dx of osteomalacia

Question 16

Describe management of vitamin D deficiency

Answer 16

Vitamin D + calcium replacement  
Ergocalciferol or colecalciferol:
6000 IU orally once a day for 8 weeks
1500 IU/day for maintenance 
Calcium carbonate (3-4 divided doses)

Question 17

What 6 parameters should be monitored when managing vitamin D deficiency?

Answer 17

Monitor 24 hr urinary calcium 
Serum calcium  
Phosphate  
ALP 
PTH  
Vitamin D

Question 18

List 3 complications of vitamin D deficiency

Answer 18

Bone deformities
Depression
Hypocalcaemia symptoms

Question 19

What is the prognosis of vitamin D deficiency?

Answer 19

Symptoms + radiological appearances improve with vitamin D tx
Bone deformities in children tend to be permanent

Question 20

What acronym can be used to memorise symptoms of hypocalcaemia?

Answer 20

CATs go NUMB 
Convulsions (seizures) 
Arrhythmias 
Tetany 
NUMBness/ paraesthesia