Osteoporosis is the most common bone disorder. It is a reduction in bone mass and alteration of bone structure, not just a reduction in bone density. The easiest way to measure the extent of the disease is with bone density scans.
- Most common bone disorder
Genetic factors are very important – in twins, concordance is 60-90%. Many genes have been implicated, and it is likely that numerous genes are involved.
- Osteogenesis imperfecta is a type of monogenic osteoporosis that has been well described, but is rare compared to multigenic and multifactorial causes. OI actually comprises of 4 subtypes, which are classified by the presence of a blue sclera. In some cases, this is apparent in childhood, but may resolve with age. In some cases, affected children are born with multiple fractures. There is also often joint hypermobility, aortic root dilation (causing aortic regurg) and hearing loss. These secondary features are related to defects in collagen.
- More common in women (4:1)
- More common in Caucasian population than in other races
- Affects 35% of the over 50s in the UK
- Post menopausal bone loss is the most common cause – this is related to oestrogen deficiency
- Malabsorption (e.g. coeliac disease)
- Most commonly the result of vitamin D deficiency
- Multiple myeloma
- Family history
- Alcohol excess
- Late menarche
- Early menopause – including surgical menopause
- Lack of weight bearing exercise
- Including Cushing’s disease
- Extreme alcohol excess
- Low calcium and/or vitamin D intake
- Reduced height (vertebral fracture)
- Stooping posture – kyphosis, aka dowager’s hump – as a result of wedge shaped fractures of the vertebral bodies.
- As opposed to osteomalacia – which occurs when bone is not being properly mineralised, despite the normal production of bone matrix.
- Decreased absorption of calcium from the gut
- Decrease muscle mass – which can affect bone remodelling by altering the normal weight bearing stressors normally exerted on bone
- Increasing osteoclast activity
Bone mineral density two standard deviation BELOW the mean value for young adults of the same sex. This is assessed using a DEXA scan.
- More mild reduction in bone density are classed as osteopenia. This is likely to progress to osteoporosis, so preventative measures may be initiated at this stage.
- The BMD is assessed on a scale relative to 0.
- >0 – better BMD than the reference
- 0 to -1 – in the top 84% of the population
- -1 to -2.5 – osteopenia
- <-2.g - osteoporosis
- Thyroid Function Test
- Vitamin D levels
- Serum immunoglobulins / electrophoresis
- Urinary Bence Jones Protein
- X-ray – not very sensitive or specific. Often osteoporosis only presents with a fracture, so you will end up doing one anyway!
- Screening programs are not widely undertaken, as their efficacy is not proven
- This can present ‘silently’, perhaps as an exaggerated kyphosis – Dowager’s Hump. This is particularly common in elderly women, and can also cause a reduction in height.
- Only 30% of vertebral fractures are symptomatic
- It may also present as acutely, especially when the nerves and nerve roots are involved.
- Thoracic spine – pain radiates around the front of the torso
- Lumbar spine – sciatic and femoral nerves may be involved.
- Sudden onset back pain
- 25% may feel nauseous and/or vomit
- Localised tenderness
- Bed rest (1-2 weeks) may be helpful
- TENS can relieve pain
- Diazepam (muscle relaxant) may also be helpful
- Initiate preventative treatments (calcitonin, bisphosphonates)
- Managed in the standard way
- Sufficient daily calcium intake – the equivalent to 1 pint of milk per day (1200-1500mg)
- Smoking cessation
- Reduction in alcohol intake
Increase weight bearing exercise
- Not only increases bone density, but also helps to prevent falls.
- At least 30 minutes weight bearing exercise 3x per week is needed to increase bone density
- 1st line – use a bisphosphonate
- 2nd line – if no improvement, try a different bisphosphonate
- 3rd line – if no improvement, try strontium
- Vitamin D
- Bind to hydroxyapatite crystals in the bone, and are then taken up by osteoclasts – resulting in a high concentration of the drugs in these particular cells. Once within the cell they:
- Cause apoptosis – by acting as analogues to ATP
- Inhibit cholesterol synthesis mechanisms – which eventually results in apoptosis
- Inhibit binding of the osteoclasts ruffled border to the bone surface – and thus the osteoclast cannot resorb the bone.
- Usually taken weekly, and with plenty of water.
- Poorly absorbed from the gut
- Should be taken on an empty stomach – as they can bind to calcium in food, after which, the drug cannot be absorbed.
- Only about 10% of the oral dose is absorbed under normal circumstances
- Pamidronate is only available IV, all other agents only available as oral preparations
- They are rapidly removed from the blood by the kidney, but as they bind to salts, they stay deposited in bone for long periods
- GI upset – which can be severe!
- Bone pain
Oesophagitis – to reduce the risk, the patient should take the drug:
- With a full glass of water
- At least 30 minutes before food
- And stay stood or sat upright for at least 30 minutes after the tablet is taken
- Most effective when started early in menopause, and continued for >5 years
- Bone loss continues, and is possibly increased upon stopping HRT
- Also increases the risks of cardiovascular disease and stroke