Metabolic bone disorders Flashcards
Define osteoporosis
A metabolic bone disease characterised by low bone mass and micro architectural deterioration of bone tissue, leading to enhanced bone fragility and a consequent increase in fracture risk.
What is the important factor when assessing severity of osteoporosis?
Assessing fracture risk
What is the name of the WHO fracture risk assessment tool? What factors does it take into account?
FRAX
- bone density
- age
- gender
- prior fracture
- family history
- smoking, alcohol
- use of steroids
- RA
Give six causes of secondary osteoporosis
Endocrine e.g. hyperthyroid, cushings Malabsorption e.g. coeliac, CF Malignancy e.g. myeloma Rheumatic e.g. RA, ankylosing spondylitis, PMR Drugs e.g. steroids, heparin... Amenorrhoea
What drugs can cause / exacerbate osteoporosis?
Steroids Heparin Warfarin Anticonvulsants PPIs GnRH inhibitors Aromatase inhibitors
List the main types of treatment for osteoporosis
Bisphosphonates
Hormone replacement therapy
Selective oestrogen receptor modulator e.g. raloxifene
Teriparatide (form of parathyroid hormone)
Monoclonal antibody - denosumab
List some risk factors for osteoporosis / reduced BMD
Increasing age Female sex Low BMI ± anorexia nervosa Parental history of hip fracture Past history of fragility fracture Corticosteroid therapy Cushing's syndrome Alcohol > 2 units/day Smoking
What bone mass density (on DEXA scan) constitutes osteoporosis?
Osteoporosis: hip BMD 2.5 SD or more below the reference mean.
Severe osteoporosis: hip BMD 2.5 SD below reference mean PLUS one of more fragility fracture.
What is denosumab? When is it used and how does it work?
A monoclonal antibody
Used to treat osteoporosis
Reduces osteoclast activity, therefore reduces bone breakdown.
Which disease(s) are caused by severe vitamin D deficiency? Describe the mechanism
Osteomalacia (adults)
Rickets (growing children)
–> inadequate mineralisation of bone matrix due to low calcium and phosphate
What is the difference between osteomalacia and rickets?
Rickets occurs if there is a vit D / calcium deficiency before the epiphyseal lines are closed.
How can rickets be fatal?
Can cause respiratory failure
Describe the presentation of rickets
Bony abnormalities e.g. leg-bowing, knock knees
Poor growth
Bone/joint pain
Delayed walking or waddling gait
Dental deformities
Severe vitD deficiency can cause hypocalcaemic seizures/tetany
Describe the presentation of mild osteomalacia
Widespread bone pain/tenderness
Proximal muscle weakness
Lethargy
Describe the presentation of more severe osteomalacia
Fatigue, bone/joint pain
Proximal muscle weakness/paraesthesia
Waddling gait /difficulty walking, adductor spasm
Spinal curvature
Signs of hypocalcaemia e.g. tetany
Pathological fractures
Skeletal deformity e.g. vertebral bodies, skull
Give one difference between osteoporosis and osteomalacia
The bone mineralisation process is normal in osteoporosis but abnormal in osteomalacia
What is osteopenia?
A reduction in bone density (-1 - -2.5; osteoporosis is -2.5)
Describe the general management for osteomalacia / rickets
Education: dietary advice (refer to a dietician).
Encourage exposure to sunlight.
Vitamin D supplementation.
Treatment of any underlying condition.
Treatment of pain.
Orthopaedic intervention may be required.
What pharmacological agents can be used in the treatment of osteomalacia / rickets?
Calciferol (vitamin D2)
What is Paget’s Disease of Bone?
A localised disorder of bone turnover. Increased bone resorption (osteoclasts) followed by increased bone formation (osteoblasts). Bone becomes disorganised and is therefore bigger, less compact, more vascular and more susceptible to deformity and fracture.
What are the typical signs/symptoms of Paget’s disease of bone?
Bone pain (constant) Bone deformity e.g. bowing of long bones.
Others: excessive heat over pagetic bone, neurological complications, hearing loss, pathological fractures.
Give a rare but serious complication of Paget’s disease of bone
Osteosarcoma
When should Paget’s disease be treated?
If present in skull If present in an area requiring surgical intervention If symptomatic (i.e. if there is bone pain)
What biochemical test can be used as a marker for Paget’s disease of bone?
Serum alkaline phosphatase (raised in Paget’s disease)
How is Paget’s disease treated?
IV Bisphosphonate therapy; single IV zoledronic acid once every 5 - 10 years.
Which disorder is colloquially known as “brittle bone disease”?
Osteogenesis imperfecta
How many types of osteogenesis imperfecta are there?
8, but only the first 4 are remotely common:
- Type I: mildest form
- Type II: lethal form
- Type III: severely progressive (deforming)
- Type IV: moderately severe
What causes osteogenesis imperfecta?
Usually due to an autosomal dominant genetic defect that causes a reduced amount/quality of type 1 collagen.
In mild OI, less collagen is produced
In severe OI, collagen chains formed are abnormal so degrade rapidly
What is the main treatment for OI?
IV bisphosphonates e.g. pamidronate
Give a characteristic feature of type I OI
blue sclera; caused by scleral thinness allowing the pigmented coat of the choroid to become visible
Give some features of OI
Bone deformity, and bone pain.
Short stature.
Spine curves.
Low Bone Density.
Loose joints, ligament laxity and muscle weakness
Distinctive features of the skull including late closing fontanels, and head circumference greater than average.
Hearing loss
Brittle teeth
Respiratory problems including asthma; may be aggravated by chest wall deformity and/or spine deformity.
Vision problems including myopia and risk for retinal detachment
Skin hyperlaxity; easy bruising.
Cardiac issues.
Fatigue.
Basilar Invagination a serious neurological problem is seen in some people with the more severe forms of OI.
Skin, blood vessels and internal organs may be fragile.
