Cortex - Biochemistry Flashcards
what is osteoporosis in general terms?
is a quantitative defect of bone characterised by reduced bone mineral density and increased porosity (i.e. the bone is of normal quality, there is just not enough of it). WHO defines osteoporosis as bone mineral density less than 2.5 standard deviations below the mean peak value of young adults of the same race and sex.
what is osteopenia?
is an intermediate stage where bone mineral density is between 1 to 2.5 standard deviations below mean peak value.
what does osteoporosis cause?
leads to fragility of the bone and increased fracture risk with fractures occurring after little or no trauma.
is loss of bone mineral density a normal physiological phenomenon ?
yes - usually occurs around the age of 30 due to a very gradual slow down in osteoblastic activity
who tends to lose more bone density - males or females and why?
females due to after the menopause there is an increase in osteoclastic bone resorption with the loss of protective effects of oestrogen.
there is 2 types of primary osteoporosis - describe type 1 and what are the further risk factors predisposing for type 1
Known as Post‐Menopausal Osteoporosis with an exacerbated loss of bone in the post‐menopausal period.
Further risk factors include smoking, alcohol abuse, lack of exercise and poor diet.
what type of fractures tend to occur in type 1 osteoporosis ?
colles fractures (a fracture of the radius in the wrist, with a characteristic backward displacement of the hand.) and vertebral insufficiency fractures.
what is type 2 osteoporosis ? and what are the risk factors which predispose people to it?
known as Osteoporosis of old age with a greater decline in bone mineral density than expected.
Risk factors are similar with the added risks of chronic disease, inactivity and reduced sunlight exposure (Vitamin D).
what fractures are commonly seen in type 2 osteoporosis ?
Femoral neck fractures and vertebral fractures predominate in this group
what can osteoporosis occur secondary to ?
conditions including corticosteroid use, alcohol abuse, malnutrition, chronic disease (CKD, malignancy, Rheumatoid arthritis) and endocrine disorders (Cushing’s, Hyperthyroidism, Hyperparathyroidism).
how is osteoporosis diagnosed ?
DEXA scanning which measures bone mineral density - values are then compared to standard peak values for race and sex
what is the aim of treatments in osteoporosis ?
they cannot increase bone mineral density so the aim of them is to slow down the decrease in bone mineral density.
describe the pharmacological treatments used to treat osteoporosis and help prevent fragility fractures
calcium and vitamin D supplements (if dietary intake is poor)
bisphosphonates (alendronate, risedronate, etidronate) which reduce osteoclastic resorption (these are considered the best treatment right now)
Desunomab (a monoclonal antibody which reduces osteoclast activity)
strontium (which increases osteoblast replication and reduces resorption)
Zoledronic acid is a once yearly intravenous bisphosphonate but is substantially more expensive than oral forms.
if side effects occur with the standard treatments used for osteoporosis what could be used ?
HRT (hormone replacement therapy) could be used but there is an increased risk of cancers and DVT’s.
Raloxifene (an oestrogen receptor modulator) could be used as another option but again there is a risk of DVT’s
what is osteomalacia ?
It is a qualitative defect of bone with abnormal softening of the bone due to deficient mineralization of osteoid (immature bone) secondary to inadequate amounts of calcium and phosphorus.
what is ricketts?
it is the same as osteomalacia but occurs in young children and subsequently has effects on the growing skeleton
what is the underlying causes of osteomalacia and ricketts?
insufficient calcium absorption from the intestine because of lack of dietary calcium
or a deficiency or resistance to the action of vitamin D
or phosphate deficiency caused by increased renal losses.
what are some of the causes of osteomalacia and ricketts?
malnutrition (Ca & vit D)
malabsorption (low vit D absorption)
lack of sunlight exposure (no activation vit D)
hypophosphateamia (re‐feeding syndrome, alcohol abuse – impairs phosphate absorption, malabsorption, renal tubular acidosis)
long term anticonvulsant use and chronic kidney disease (reduced phosphate resorption & failure of activation vitamin D).
what are the signs and symptoms of osteomalacia and ricketts?
Patients may complain of bone pain (pelvis, spine and femora), have deformities from soft bones (particularly rickets), sustain pathological fractures easily and have symptoms of hypocalcaemia (paraesthesiae, muscle cramps, irritability, fatigue, seizures, brittle nails).
what may radiographs show for patients with ricketts and osteomalacia ?
pseudofractures (aka Looser’s zones)
what is the difference in bone biochemistry when comparing osteoporosis to ricketts and osteomalcia ?
serum bone biochemistry is abnormal with typically a low calcium, low serum phosphate and high serum alkaline phosphatase - for osteomalacia and ricketts wheres its normal for osteoporosis.
what is the treatment of osteomalacia and ricketts ?
Treatment involves vitamin D therapy with calcium and phosphate supplementation.
what is hyperparathyroidism?
it is overactivity of the parathyroid gland with high levels of PTH
what is primary hyperparathyroidism and what is it caused by ?
due to a benign adenoma, hyperplasia or rarely a malignant neoplasia
Overproduction of PTH results in hypercalcaemia with subsequent symptoms and signs (fatigue, depression, bone pain, myalgia, nausea, thirst, polyuria, renal stones, osteoporosis). Serum PTH is usually elevated and calcium is high. Phosphate is normal or low.
