Osteoporosis Flashcards
What is osteoporosis?
“porous bone”
It is a metabolic bone disease characterized by:
- low bone mineral density
- microarchitecture disruption (impaired mineralization)
- decreased bone strength
- increased risks of fractures
(Due to excessive bone resorption - incr osteoclast activity and decreased bone formation - reduced osteoblast activity)
Causes for decreased bone mass
- Age - osteoblast lose activity
- Menopause - low estrogen increases bone resorption
- Low serum calcium - malnutrition, malabsorption
- Alcohol consumption - incr RANKL, incr oxidative stress, apoptosis of osteoblast
- Smoking - dose and duration dependent, affects the metabolism of estrogen, incr RANKL
- Physical inactivity - muscular skeletal not used, bone deposition dcr due to lack of stress, bone resorption increase
- Malnutrition (e.g., anorexia, bariatric surgery/gastrosurgery) - IC10
- Medication use
- Secondary to other diseases
What are some medications that can cause decreased bone mass?
- Chronic glucocorticoid use
- Long-term PPI
- Cancer chemotherapy
- Immunosuppressants (cyclosporine)
- Antiseizure medications (PHT, phenobarbital)
- Aromatase inhibitors
- GnRH agonist and antagonist
- Heparin (anticoagulants)
How does glucocorticoid cause reduced bone mass?
- Dcr calcium absorption from the gut through antagonism of Vit D
- Accelerate bone resorption and inhibit bone formation through inducing the decrease in osteoblast differentiation and increasing apoptosis of osteoblasts and osteocytes
What are some diseases that can cause reduced bone mass?
- Endocrine disturbances (Cushing’s, hyperprolactinemia, hyperparathyroidism, hyperthyroidism, hypogonadism, diabetes mellitus)
- GI disease
- Marrow-related disorders
- Organ transplantation
- Genetic disorders
Clinical manifestations/Presentation of osteoporosis
- Asymptomatic
- Often undiagnosed until presented with episode of low-trauma fragility fracture, can involve:
- Spine (vertebral compression) - height loss of >=20% dcr in vertebral height; kyphosis - excessive curve of the spine, bending over
- Hip (femoral neck)
- Wrist (distal radius)
- Humerus
- Rib
- Pelvis
Note that low-trauma fragility fractures means they occur as a result of minimal trauma such as fall from standing height or less, or no identifiable trauma
These bones consist mainly of spongy bones
- Fragility fracture can cause pain and disability, increase healthcare cost, NH placement, and mortality
Histological features
- Fewer trabeculae in the spongy bone
- Thinning of cortical bone
- Widening of haversian canals
=> increase risk of fragility fracture
Goals of osteoporosis treatment
- Prevent fracture - either recurrent future fracture or first fracture
- Improve QoL and reduce economic burden
[Determining who to screen]
Which group of individuals should be further assessed for risk factors for osteoporosis and fragility fractures?
What are the risk factors?
Assess the following individuals for osteoporosis and fracture risk (if any of the risk factors are present):
- Post-menopausal women
- Men >=65 years
Assess the following risk factors in the above population:
- Family history of osteoporosis or fragility fractures
- Previous fragility fracture
- Ageing
- Low body weight
- Height loss (>2cm within 3y)
- Early menopause (45y and younger)
- Certain medications: e.g., chronic glucocorticoid (>5mg/day prednisolone or its equivalent for >3m in the past year)
- Low calcium intake (<500mg/day)
- Excessive alcohol intake (>2 units/day)
- Smoking
- Prolonged immobility
- History of falls
- Presence of diseases that can lower bone mineral density or increase fracture risk (e.g., DM, hypogonadism, inflammatory rheumatic diseases such as RA)
[Determining who to screen]
Assessment for post-menopausal women:
OSTA score - osteoporosis self-assessment tool for Asians
= age in years - weight in kg
- High risk >20: consider DXA scan as change of low BMD is high
- Medium risk 0-20: consider DXA scan if any other risk factors for osteoporosis is present
- Low risk <0: consider deferring DXA
If patient initially deemed low risk, reassess risk if there has been significant weight loss or any clinical risk factor development since the last visit, or if last assessment was >=5 years ago
Diagnosis of osteoporosis:
When to start treatment?
Diagnosis (given by first 2 scenarios)
3 scenarios to start treatment:
- History of fragility fractures - DXA not required
- that occurred spontaneously or from minor trauma that would not ordinarily result in fracture; at vertebral/hip/wrist/humerus/rib/pelvis
- asymptomatic vertebral fracture can be identified as >=20% decrease in vertebral height
- Bone mineral density (BMD) measurement using DXA hip and/or spine
- T-score =< -2.5 SD (osteoporosis)
- T-score > -2.5 SD to <-1 (osteopenia)
- T-score >= -1 (normal bone density)
- Osteopenia (T-score > -2.5 SD to <-1) + Frax score (10y probability risk) - not osteoporosis, but high risk hence start treatment
- Major osteoporotic fracture >= 20%
or
- Hip fracture (>=3%)
If patient initially deemed low risk, give lifestyle advice and reassess risk if there has been significant weight loss or any clinical risk factor development since the last visit, or if last assessment was >=5 years ago
What is a DXA scan, and how to use the results?
Dual-energy X-ray absorptiometry (T-score)
- Scan at two places: 1. Hip (femoral neck) 2. Spine
- Hip scan has higher predictive value for hip fracture and fracture risk
- Spine scan is quick and preferred for assessing response to treatment, but not suitable for diagnosis in older people because of high prevalence of degenerative changes, which may artefactually incr BMD value
May consider adding Vertebral Fracture Assessment (VFA) or thoracolumbar (TL) X-ray to identify vertebral fractures in older adults with height loss or lower back pain
Difference between T-score and Z-score
T-score compares BMD against a young adult reference population (ladies in the 20s)
Z-score compares BMD against expected BMD for patient’s age
- Therefore, Z-score values are not as bad as T-score
- Z-score of =< -2 SD suggests coexisting problems (e.g., glucocorticoid therapy, alcoholism) that can contribute to osteoporosis
Clinical history, Physical Examination, and Labs required to exclude secondary causes of bone loss:
(E.g., esp if Z-score =< -2)
Common:
- Creatinine - renal function affects choice of drug, also may indicate CKD-MBD
- FBC - exclude other disorders such as malignancies and malabsorption
- Corrected calcium
- Vit D
Others:
- Thyroid-stimulating hormone - hyperthyroidism
- Erythrocyte sedimentation rate (ESR) - rheumatological disease
- Alkaline phosphatase - liver disease, Paget’s disease
- Serum phosphate
- Spot urine calcium/creatinine ratio
- Serum total testosterone - hypogonadism
How to assess FRAX score?
FRAX score: 10y probability of developing a fracture
Risk factors used to calculate FRAX score:
- Age
- Sex
- Weight
- Height
- Previous fracture
- Parent fractured hip
- Current smoking
- Glucocorticoid (5mg daily Prednisolone for >3m)
- Rheumatoid arthritis
- Secondary osteoporosis
- Alcohol 3 or more units per day
- BMD - key in the worse one
Prior clinical vertebral fracture or hip fracture is an especially strong risk factor, fracture probability computed may be underestimated
Smoking, alcohol, glucocorticoids are dose-dependent risk factors, the higher the exposure, the greater the risk
RA is a risk factor for fracture, OA is protective
When to refer to a specialist?
What are some considerations before referring?
- CrCl <30ml/min (might suspect CKD-MBD)
- Complex secondary cause
- Patients with multiple fragility fractures AND very low DXA BMD (T-score < -3.0)
- Patients who adhere to treatment and who experience multiple fragility fractures or continued bone loss (>4-5% deterioration in DXA BMD) after at least a year of treatment
Consider (for the last point above):
- reviewing secondary causes of osteoporosis
- switching to IV or SC therapy to negate problems of poor gut absorption or poor compliance with PO therapy
