chapter 21 - metabolic bone disease Flashcards
name the 3 main groups of metabilic bone disease
osteoporosis
osteomalacia
osteitis fibrosa
define osteoperosis
abnormal decrease in bone mass per unit volume
mechanism of osteoperosis
low bone mass –> subsequent resorption –> increased bone fragility + increased tendency to fracture
what is the cause of primary osteoporosis
post menopausal osteoporosis
rate of bone loss post menopause relative to before?
pre: 0.3% per year
post: 3% per year
how does menopause affect the bones?
decreased estrogen - therefore increased osteoclastic activity
risk factors for primary osteoporosis - 6
caucasian hereditary premature menopause early hysterectomy smoking alcohol abuse
clinical features of primary osteoporosis -3
back pain
thoracic kyphosis
fracture of distal radius - often initial event
3 investigations for the diagnosis of osteoporosis
xray
dexa scan
bone turn over and biochemical tests - usually normal
xray features of osteoporosis
wedging of vertebral bodies
end plate collapse
loss of normal trabecular pattern of bone
treatment of osteoporosis
- prevention: normal diet + atleast 1500mg ca per day from 20 yrs of age
- avoid RF
- HRT
- calcitonin or bisphosphonates if HRT CI
most effective therapy for osteoporosis
HRT
why must you monitor patients on HRTs ?
slightly increased risk of breast and uterine cancer
what is senile osteoporosis?
15 yrs after menopause and at the same age in men there is still a 0.5% decline in bone mass per year –> may lead to increased fractures from minor trauma
RF for senile osteoporosis
prolonged menopausal bone loss chronic illness urinary insufficiency muscular atrophy dietary deficiency lack of exposure to sunlight increased tendency to fall
typical fracture found in patients with senile osteoporosis
fracture of femoral neck of minor trauma
treatment of senile osteoporosis
- manage fracture
- optimise medical condition
- sodium fluoride + vitamin D may increase bone mass
- bisphosphonates may minimise further loss
causes of secondary osteoporosis - 6 broad groups
nutritional endocrine drug malignant disease non malignant disease other
nutritional causes of secondary osteoporosis 3
scurrvy
malnutrition
malabsorption
4 endocrine causes of secondary osteoporosis
hyperparathyroidism
gonadal insufficiency
cushings disease
thyrotoxicosis
4 drug induced causes of 2 osteoporosis
corticosteroids
alcohol
nicotine
heparin
3 malignant diseases causing secondary osteoporosis
carcinomatosis
leukemia
multiple myeloma
4 non malignant diseases causing secondary osteoporrosis
rheumatoid arthritis
ankylosing spondylitis
tuberculosis
chronic renal disease
other causes of secondary osteoporosis 2
weightlessness - space workers
immobilisation
what is the mechanism of rickets and osteomalacia?
inadequate mineralisation of bone
which population presents with rickets ?
children
which population presents with osteomalacia?
adults
which areas are affected in rickets
areas of endochondral growth
which areas are affected in osteomalacia?
areas of new bone in the skeleton is incompletely calcified and structurally weak
3 reasons for inadequate bone mineralisation
- calcium deficiency
- hypophosphataemia
- aberrant metabolic pathway for vitamin D
5 causes of aberrant metabolic pathway for vitamin D
- nutritional
- lack of sunlight
- intestinal malabsorption
- decreased 25 hydroxylation - liver disease/ anticonvulsants
- reduced 1 alpha hydroxylation - renal disease
8 clinical features of rickets
1 failure to thrive
2 tetany, convulsions
3 muscular flaccidity
4 deformity of skull - craniotabes
5 thickening of ankles knees and wrists from epiphyseal overgrowth
6 enlargement of costachondral junctions - rickety rosary
7 lateral indentation of chest - harrisons sulcus
8 bow legs, coxa vara, spinal deformtiy, fractures of long bones
what is craniotabes?
skull deformity in rickets
what is rickety rosary
enlargement of costachondral junctions
what is harrisons sulcus
lateral indentation of chest
4 clinical features of osteomalacia
more insidious than rickets
bone pain
weight loss
stress or insufficiency fracture
radiological features of rickets 2
thickening and widening of the growth plate
bowing of the diaphysis
radiological features of osteomalacia 3
looser zone
biconcave vertebrae
trefoil pelvis
what is the loosers zone?
a transverse band of rarefaction in an otherwise normal bone - osteomalacia
what is trefoil pelvis?
lateral indentations into the pelvis by the acetabulae - osteomalacia
biochemistry of rickets and osteomalacia
- decreased serum calcium and phosphate
- increased alkaline phosphatase
- diminished urinary excretion of calcium
- in vitamin D deficiency 25 HCC levels are low
- diminished calcium phosphate product ( < 2.4mmol/l)
which value of calcium phosphate product is diagnostic for rickets and osteomalacia
< 2.4mmol/l
in some cases of rickets and osteomalacia another investigation is needed - what is this ?
bone biopsy
