Metabolic Bone Disease Flashcards
Which groups are at risk of vitamin D deficiency?
- Those with Renal / Hepatic disease
- The elderly
- Those with darker skin (melanocytes compete for UV rays)
Which hormone is implicated in the removal of calcium from bone? How is calcium partitioned within the body?
Parathyroid hormone
Calcium is used to harden bone, but also acts as a very important cellular messenger. The body prioritizes cellular messages, often at the expense of bone. Hard to maintain Ca homeostasis with liver / kidney disease
Describe the pathophysiology of Paget’s bone disease
Disease of bone turnover. Excessive bone resorption followed by excessive bone formation
Leads to disorganized bone that is bigger, less compact, more vascular and more susceptible to deformity and fracture
Who is most likely to get Paget’s disease?
- Strong genetic component
- Anglo saxon heritage
- Hypothesized that viral infection may act as environmental trigger
- > 40 years old (mainly 70+ yrs old)
- More common in females
Presentation of Paget’s disease?
- Bone pain (often worse at night)
- Bone deformity (some cases)
- Heat over affected bone
- Hearing loss (often due to CN VIII compression)
(most commonly diagnosed incidentally when raised ALP is found during LFTs)
Which bones are commonly affected by Paget’s diesease?
Long bones: femur, tibia & fibula, radius & ulna
Pelvis
Skull
(can affect any bone within skeleton though)
Investigations for suspected Paget’s disease?
- X-ray
- Isotope bone scan (increased metabolic activity of bone will show on scan)
- Bloods: elevated ALP
Treatment of Paget’s disease?
No indication to treat asymptomatic Paget’s unless in skull or area requiring surgical intervention
- One off IV infusion of Bisphosphonates (zoledronic acid) is the mainstay of treatment
- Calcitonin if severe pain
Describe the pathophysiology of Rickett’s disease / Osteomalacia
Severe vitamin D deficiency causes insufficient mineralization of bone: Rickett’s / Osteomalacia
No vitamin D = no calcium absorbed in gut and therefore no bone mineralization
Who tends to get Rickett’s / Osteomalacia?
Rickett’s: children (epiphyseal plates still exist)
Osteomalacia: adults (epiphyseal plates closed)
Presentation of Rickett’s disease?
- Stunted growth
- Abnormal bone shape (eg splayed epiphyses)
- Frontal bossing (large skull / prominent forehead)
- Rachitic Rosary ribs (beads under rib cage on radiograph due to overgrowth of costal cartilage)
- Bowed legs
- Protruding abdomen
Treatment of Rickett’s diease and osteomalacia?
Calcium and vitamin D supplements
underlying endocrine problem?
Symptoms / signs of osteomalacia?
- Bone pain / tenderness
- Bony deformities
- Altered muscle function / myopathy
- Increased falls risk (fall frequency)
Investigations for osteomalacia / Rickett’s?
- X-ray (Looser’s zones: microfractures - radiolucent areas)
- Bloods: Ca / PO4 / ALP / PTH / vit. D
What is osteogenesis imperfecta?
Genetic disorder (28 different types) of type 1 collagen resulting in weak bones that are extremely vulnerable to fracture
Broad clinical range - can be lethal at young age, can present similarly to early onset osteoporosis
What are the four types of osteogenesis imperfecta? Brief description of each
Type 1 - mild form, begins when child starts to walk or later on, even in to adulthood
Type 2 - lethal by age 1
Type 3 - progressive deforming with severe bone dysplasia and poor growth
Type 4 - similar to type 1 but more severe
What are some signs of osteogenesis imperfecta?
- growth deficiency / defective tooth formation
- Hearing loss
- Blue sclera
- Scoliosis / barrel chest
- hyper-mobility & easy bruising
Treatment of osteogenesis imperfecta?
- Surgical: to treat fractures
- Pharma: IV Bisphosphonates, fracture prevention
- Genetic counselling & social education
What is osteoporosis defined as?
Metabolic bone disease characterized by low bone mass and deterioration of bone tissue leading to bone fragility and increased fracture risk
What are some factors that affect a patients fracture risk? What are some softwares commonly used to calculate fracture risk?
- Age
- Sex
- BMI
- Previous fracture
- Genetics (has parent broken a hip?)
- Smoking / steroid use / RA / secondary osteoporosis / booze
FRAX (WHO) and Q Fracture (UK)
What is a DXA scan?
dual-energy x-ray absorptiometry
Used to measure bone mineral density (BMD)
What is the T score from a DXA scan? How do the results of a DXA correspond to fracture risk?
The number of standard deviations in BMD that a patient is below that of the standard young adult range
the young adult range has to be taken from young adults of similar BMI, race and sex
For every standard deviation below there is a doubling of the risk of a low trauma fracture
What T score corresponds to osteoporosis?
2.5 + standard deviations below
Truly only applies to post-menopausal women but used in a variety of cases
What is a Z score from a DXA scan?
A comparison between the bone mineral density of a patient and their absolute peer group
Absolute peer group is comprised of patients of the same age, race, sex and BMI
What are the three most common types of DXA scan?
- DXA scan of spine (useful in youngers)
- DXA scan of hip (useful in the elderly)
- Lateral DXA (identify spinal fracture etc.)
Who should be referred for a DXA scan?
- Patients on oral steroids
- Patients who have suffered a low trauma fracture
- Those at risk of osteoporosis
Who is at risk of an osteoporotic fracture?
- The elderly F > M Endocrine disease Rheumatic disease Inflammatory diseases (UC and Crohns) Liver disease Malabsorption (CF / pancreatitis / coeliac etc.) Smokers / Boozers
What are some endocrine disorders that predispose an individual to osteoporosis?
- Hyperthyroidism
- Cushings
- Low sex hormones
- Hypo and hyper parathyroidism
- Hyperprolactinaemia
- Hypopituitarism
What are some medications that may lead to the development of osteoporosis?
- Corticosteroids**
- PPIs
- Anti epileptics
- Aromatase inhibitors (used to treat breast cancer)
- GnRH inhibitors
- Warfarin
How does bone mass change with time?
- Increases through puberty, maxes out late 20s
- 20 - 40s maintain peak (except in those w risk factors)
- 40 begins to decrease
- Menopause triggers accelerated decrease
- Gradual decrease in the elderly (60+)
What are some medication options for the treatment of osteoporosis?
- Oral Bisphosphonates*** (not suitable for low eGFR)
- Denosumab (monoclonal antibody against RANKL)
- Teriparatide
- Hormone replacement therapy (HRT)
- Selective Oestrogen Receptor Modulator (Raloxifene) (don’t protect the hip)
What are some side effects of hormone replacement therapy (HRT)?
- Increased risk of blood clots
- Increased risk of breast cancer with extended use
- Increase risk of heart disease and stroke if used after a large gap since menopause
How do bisphosphonates work?
- Bone bone mineral
- Gets absorbed by osteoclast along with mineral
- Bisphosphonate poisons the osteoclast causing apoptosis
- Bisphosphonate and bone mineral are redeposited
Are bisphosphonates taken for the rest of the patients life once diagnosed with osteoporosis?
- Usually take a 1-2 years off the bisphosphonates every 5 or 10 years to avoid excess toxicity
- But since it occurs in old geeza’s that may be the rest of their life
What is the function of denosumab? How is it given and how often? Who can take it that can’t take bisphosphonates?
- Reduces osteoclast resorption by binding RANKL
- Subcutaneous injection every 6 months
- Suitable down to eGFR of 15, predialysis patients
Which cells set the rate of bone turnover? Describe
- Osteoblasts.
Lay down their bone and then release RANK ligand to stimulate osteoclast activity
What is teriparatide? How often is it given + formulation?
- It is the first 34 AA’s of PTH
- Single daily injection
