Bone Disease Flashcards
What is Osteoporosis?
Disease characterised by reduced bone mineral density & microarchitectural deterioration of bone tissue
-leads to inc bone fragility/inc risk fractureq
How does bone mass change over a normal lifetime?
Bone mass peaks at 20-30yrs
Falls in post menopausal women
-due to oestrogen deficiency
What are the risk factors for Osteoporosis?
Age Female sex Genetics Low peak bone mass Disuse Smoking
What are the secondary causes of Osteoporosis?
Primary hyperparathyroidism Thyrotoxicosis Steroid-induced Cushing's disease Anorexia nervosa Malabsorptive conditions Chronic inflammatory/neoplastic disease
How does Primary Hyperparathyroidism cause Osteoporosis?
High PTH increases bone turnover
How does Thyrotoxicosis cause Osteoporosis?
Increases bone turnover
How do Steroids cause Osteoporosis?
Dec intestinal Ca absorption & inc renal Ca excretion
-leads to 2o hyperparathyroidism
Direct inhibition of osteoblast activity & stimulation of osteoblast apoptosis
How does Cushing’s Disease cause Osteoporosis?
As per steroids
How does Anorexia Nervosa cause Osteoporosis?
Ca deficiency
Wt loss
Hypogonadism
How do Malabsorptive conditions cause Osteoporosis?
Ca deficiency
2o hyperPTH
How does chronic inflammatory/neoplastic disease cause Osteoporosis?
Increase bone resorption
Suppress bone formation
How does Osteoporosis present?
Mainly asymptomatic Fragility fractures Back pain Height loss Kyphosis
What are the most common sites for osteoporotic fractures?
Wrist (Colles)
Neck of Femur
Spine (vertebral crush/wedge fracture)
What investigations may be appropriate in suspected Osteoporosis?
BMD measurements using DEXA -measured at lumbar spine/iliac crest -gives T-score Serum Ca/phosphate TFTs ESR Sex hormone panel Vit D/PTH
What T-scores reflect Osteopenia?
-1 to -2.5
What T-scores reflect Osteoporosis?
What is a FRAX score?
Screening tool used in GP for pts >50yrs
-estimates risk of fragility fracture
What lifestyle advice should pts w/ osteopenia be given?
Stop smoking
Limit alcohol intake to <20 units/week
Increase exercise
Increase dietary Ca intake
What management is available for pts w/ osteoporosis?
Weekly bisphosphonates (aldendronic acid) 1st line Vit D HRT Testosterone replacement therapy Calcitonin Recombinant PTH
How do bisphosphonates work?
Decrease bone resorption
Allow mineralisation of existing bone
What are the main s/e of bisphosphonates?
GI s/e
Osteonecrosis of jaw
What is Osteomalacia?
Inadequate bone mineralisation
-usually caused by Vit D defiency
How does Osteomalacia present?
Bone pain
Bone fragility/fractures
Malaise/weakness (can be insidious onset)
What is Rickets?
Syndrome resulting from osteomalacia in growing skeleton
-bone deformity and sx of osteomalacia
How is Vit D synthesised?
7-dehydrocholesterole in skin + UV light = cholecalciferol
How is Vit D metabolised?
Cholecalciferol metabolised in liver/kidneys
- produces 1,25-dihydroxycholecalciferol (calcitriol)
- inc ca uptake, dec ca excretion
What is the underlying pathophysiology of Osteomalacia?
Vit D deficiency –> low plasma Ca –> 2o hyperPTH
-stimulates osetoclastic bone resorption
-decreases ca excretion
-increases phosphate excretion
Progressive loss of Ca/PO4- from bone –> defective mineralisation
What are the common causes of Vit D deficiency?
Inadequate dietary intake (vegans, malabsorption)
Inadequate synthesis (housebound pts, muslim women)
Renal disease (CKD)
Liver disease
Drugs
What are the features of Vit D deficiency?
Insidious onset
- bone pain
- pathological fractures
- general malaise
- proximal muscle weakness, waddling gait
What blood tests should be done in a pt presenting w/ Osteomalacia?
U&Es ALP (high) Plasma Ca (normal/low) Serum PO4 (low) Serum PTH (high) Serum Vit D (low)
What are the X-ray signs of Osteomalacia?
Normal Looser zones of defective mineralisation -long bone -pelvis -ribs Widening of epiphyseal plate (children)
What is the management of Osteomalacia?
Oral Vit D replacements
-high dose for 4 weeks, then maintenance
What are the rare causes of Osteomalacia?
Hypophosphataemia
Bisphosphonates
Fluoride/Aluminium intoxication
What is Paget’s Disease of Bone?
Common disease of unknown origin affecting bones in elderly
How common is PDB?
10% at 85yrs
What is the underlying pathophysiology of PDB?
Excessive uncontrolled resorption of bone by large, abnormal multinucleated osteoclasts
Destruction of cortical/trabecular bone in waves
New bone is women, non-lamellar w/ fibrosis of marrow spaces
What are the clinical features of PDB?
80% asymptomatic Waxing/waning bone pain Bone deformities (bowed tibia/skull changes) Cranial nerve palsies (CN VIII) Cardiac failure
What is the classical presentation of PDB?
Bone pain
Pathological fractures
Deafness
What is the main complication of PDB?
30x inc risk of developing osteogenic sarcoma
What investigations may be appropriate in suspected PDB?
Bloods - ALP, Ca, PO4 (normal)
Urine - raised hydroxyproline
XR - variable presentation, sclerotic & lytic lesions
Bone scans
What use are bone scans in PDB?
Show extent of bone involvement
Cannot differentiate b/w Paget’s & Sclerotic Mets
What is the management of PDB?
Analgesics
Bisphosphonates
Monitor serum ALP
Surgery for 2o joint disease/neurological complications
What is Osteonecrosis?
General term for ischaemic bone necrosis
How long does Ischaemia take to cause Osteonecrosis?
W/ ischaemia bone marrow dies w/i 12hrs, bone cells die b/w 12-24hrs
Describe osteonecrosis in the shaft of a long bone
Bone infarction
Involves trabecular bone & bone marrow in medulla
Describe osteonecrosis in the epiphysis of a long bone
Avascular necrosis
Involves trabecular bone, bone marrow & cortical bone
What are the common causes of osteonecrosis?
Interrupted arterial supply (fractures)
Interrupted venous drainage
Retrograde arterial stoppage
What are the risk factors for osteonecrosis?
Fracture (subcapital NOF, scaphoid fracture)
Idiopathic (Perthe’s, AVN of fem head)
Bone marrow infiltration (malig)
Alcohol abuse
Cushing’s/exogenous corticosteroids/chemo
Infection (SA)
Which bones are most susceptible to osteonecrosis?
Head of femur
Proximal scaphoid
Lunate
Body of talus
How does osteonecrosis present?
Pain
Stiffness
Swelling in local joint/over bone
What are the XR signs of osteonecrosis?
Distinctive segment of inc bone density
-present after 6mo
What is the management of osteonecrosis?
Eliminate cause Prevent complications (potential surgical intervention)
