metaboolic bone disease Flashcards
too much osteoclast
bone wasting diseases
too much osteoblast
sclerosing bone disease
osteoperosis
porous bone
bone wasting disease
a skeletal disorder characterised by compromised bone strength predisposing to an increased risk of fracture
bone wasting disease example
osteoperosis
example sclerosing bone disease
osteopetrosis (stone bone)
sclerosteosis
bone strength
bone density + bone quality
bone density
grams of mineral per volume (BMD, bone mineral density)
bone quality
architecture, turnover, damage
osteoporosis incidence
most common metabolic bone disease
endemic in wester society
a fracture resulting from a fall of standing height or less due to osteoporosis
osteoperotic-related fragility fracture
1 in 2 women and 1 n 3 men will suffer this sort of fracture
usually wrist, vertebrae or hip
mortality of osteoporosis
hip and vertebral fracture mortality
risk of death is greatest immediately after fracture
death is not directly attributed to the fracture but rather other chronic diseases that lead to the fracture
morbidity of osteoporosis
7% of survivors of fracture have some sort of permanent disability
hip fractures most often associated with osteoporosis-disabilities
eg. pressure sores, UTIs etc, 50% unable to independently walk after fracture
pathophysiology of osteoporosis
remodelling - imblanace in processes whch are responsble for acquision and maintenance of bone mass
increase in resorption of bone
type 1 osteoporosis
post menopausal
only effects trabecular bone
forearm and spinal fractures most common
type 2 osteoporosis
age related
cortical and trabecular bone
hip fracture more common
secondary osteoporossis
arises from other causes: usually endocrine diseases (cushings, hypogonadism, hyperparathyroidsm), drugs (anti-retrovirals), glucocorticoids, malabsorbtion, and rheumatological diseases
histology og osteoperosis
trabecular and cortical thinning
increased adiposity in marrow
smaller osteoid seams
normal bone width
clinical features of oosteoporosis
mostly asymptomatic - pain - microfactures - fractures hip, vertebral bodies, radius
clinical diagnoss of osteopoross
serum biochemistry - typically with normal limits alkaline phosphatase (ALP - osteoblast marker) carboxy terminal telopeptide of type 1 collagen (CTX, bone resorption osteoclast marker) - serum calcium and serum phosphate
if CTX is raised this may indicate
Carboxy terminal telopeptide of type 1 collagen
could ndicate secondary osteoporoosis
clinicall diagnosis of osteoporosis using X ray
insensitve means of detection
decreased bone density
cortical thinning
fracture
gold standard clinical diagnosis of osteoporosis
densitometry
densitometry
DEXA-T scores
bone mineral density as assessed by Dual-Energy X ray Absorptiometry
difference nbetween measures and mean ‘healthy’ (based on matched gender and ethnic group)
T score > -1
normal
T score -1 ro -2.5
ostopaenia
T score < -2.5
osteoporosis
T score < -2.5 and H. of fracture
severe osteoporosis
T score represents
T score represents the number SD a patient is above or below the mean BMD of a young adult
osteomalacia
defective minelarlisation of organic matrix
bone softening
rickets (children) osteomalaca (adults)
pathophysiology of osteomalacia
impaired metabolism
most commonly caused by severe vit D deficency
lack of mineralisation effects both quality and quantity of bone
reduced stifness and stength, susceptibe to compressive forces
deformities of weight bearing bones
pathological fractures
dietary deficiencies of osteomalacia
vit D, calcium, phosphate
vitamine D lack may be caused by
endogenous synthesis reduced (lack of sunlight) dietary lack (malabsorbtion) chronic renal failure, hepatic disease
aetiology of rickets
- vit D lack or resistance
- hypophosohatamia
- drugs: phenytoiin, aluminium, heavy metals
- neoplasia - oncogenic osteomalacia
clinical features of osteomalacia
- bone is soft (deformity) and fragile
- bone pain/tenderness
proximal muscle weakness (hypocalcaemia)
general low bone mass on radiology
multiple bilateral cortical lucensies (pseudofractures)
biochemistry of osteomalacia
alterations in the serum concentrations of calcium, phosphorous, vitamin D
vary according to the underlying disorder but tend to show: low/normal serum calcium, low phosphate, high ALP
rickets in children
shortened heght due to disruption of metaphysis
warping of femurs
primary hyperparathyroidism
parathyroid adenoma, parathyroid hyperplasia
parathyroid carcinoma
secondary hyperparathyroidism
chronic hypocalcaemia
lack of negative feedback
hypersecretion of PTH
pathophysiology of primary hyperparathyroidism
primary excessive uncontrolled production of parathyroid hormone (PTH) from neoplastic of hyperplastic parathyroid tissue
parathyroid hyperplasia/adenoma/carcinoma
excessive PTH stimulates osteoclastic resorpton
results in marked hyperclacemia
effects of excessive PTH
increased bone resorption by osteoclasts
mobilisation of Ca/PO4
osteoclastic > osteoblastic activity
diffuse osteopaenia
cysts (macro or micro)
marrow fibrosis
brown tumours (rare) large localised areas of resorpton (jaw, skull, long bones)
clinical presentation of hyperparathyroidsim
asymptomatic (biochemical abnormality detected incidentally)
signs and symptoms of hypercalcaemia - abnormal cramps, constipation, muscle fatigue, peptic ulceration, renal calculi
bone related disease
diagnosis hyperparathyroidism
primary/secondary bone changes are identical on radiology
dissecting/tunnelling bone resorption
thinnng cortical and trabecular bone
irregularr new bone formation
x-rays = diffuse osteopaenia and/or circumscribed lucencies subperiosteal eg. phalanges - erosion of tufts
hyperparathyroidism microscopically
increased osteoclast number and activity wth increased bone resorpton, which a characteristic tunneling or dissecting pattern
mesenchymal cells proliferate in the marrow space and fibrous tissue replaces lost bone
paget’s disease
osteitis deformans
characterised by disordered bone remodelling
3 phases of paget’s disease
- osetolytic (hyperactivated/large and hypernucleated osteoclasts)
- mixed (lytic and blastic)
- osteoblastic/sclerotic phases
results in thick, soft, porous bone, prone to compression and deformity
aetiology of paget’s disease
idiopathic disorder relatively common late adult life virus (paramyxovirus inclusions) genetic
paget’s disease my involve
one bone - monostotic
multiple bone - polyostotic
most commonly pelvis and skull but virtually any bone
paget’s disease sites/symptoms
skull - sskull enlargement, cranial nerve compression
thoraco-lumbar spine - pain, neurological cord compression
pelvis sacrum - pain, joint involvement - arthritis
femur, tibia - pain, deformity, pathological fracture
also associates with high ooutput congestive heart failure due to increased shunting of blood to bones
bones are hypervascular and hot
paget’s disease - diagnosis
often asymptomatic
x ray elevated serum ALP and urinary hydroxyproline
normal serum calcium and phosphorous
rradiology description
earrly signs of pagets
radiolucency
late signs of pagets
increased bone density
increased microfractures
loss of distinction between cortex and medulla
may have sharp demarcation between normal and affected bone
may extend into soft tissue if florid disease
histology of pagets
increased osteoclastic and oosteoblastic activty
acute - primarily women bone, focal mosaic pattern of lamellar bone, resembled jigsaw puzzle with prominent irregular cement lne - osteoclasts present at surface of bone but dont tunnel, in osteollytic phase, hypernucleated osteoclasts may have up to 100 nuclei
chronic - thick trabeculae and thicker bones, highly vascullar fibrocellular marrow replacing the haematopoietic marrow
