Osteoporosis

Definition

This poor man has suffered from a loss of height, as a result of his reduced bone density.

Loss of bone density sufficient to increase the risk of fracture.

Epidemiology

Osteoporosis is a common condition, either as a primary disease, secondary to another disease or as a side-effect of medication. It affects:

• 1 in 3 women >50 years
• 1 in 12 men > 50 years.

Pathophysiology

Bone is constantly forming and reforming. In osteoporosis, the balance between bone resorption and formation is out of whack (i.e. too much resorption). This causes bones to be weak. There are a variety of factors that can effect this but these risk factors will be explained in turn below.

Bone density changes over time and reaches its peak bone mass. If this peak bone mass is not reached for whatever reason, the likelihood of osteoporosis increases.

Risk Factors

Corticosteroid therapy

Steroids are a commonly used therapy in a variety of specialties. However, corticosteroids like prednisolone increase the risk of osteoporosis developing. (How? I'm not exactly sure at the moment. Let's say the pathophysiology is "magic" for now.)

• Patients >65y on therapy ≤3 months should be on prophylaxis/treatment. No BMD check required.
• Patients <65y should have BMD measured
• If T score is < -1.5, treatment should be considered
• BMD should also be considered in patients taking steroids recurrently

Hormonal problems

Cushing's syndrome is often caused by corticosteroid therapy but in itself is a risk factor for osteoporosis. Primary hyperparathyroidism has an effect as parathyroid hormone is an important regulatory factor in bone remodelling. PPremature menopause also increases risk of osteoporosis due to the protective effect of oestrogen on bone. Primary hypogonadism is a rare risk factor.

Food and weight

• Low body mass (BMI<19kg/m²)
• Anorexia nervosa
• Poor diet (particularly calcium)
• Malabsorption e.g. coeliac disease

Potentially modifiable risk factors

• Sedentary lifestyle - weight bearing and stressing bones stimulates bone formation
• Prolonged immobilisation (same rationale as above)
• Smoking

Other factors

• Chronic disease e.g. rheumatoid arthritis
• Age >60
• Family history
• Maternal history
• Post transplant
• Chronic renal failure

Clinical Features

The main way that osteoporosis presents is through fractures. Unfortunately, if you have weak bones, that's what tends to happen first. It doesn't really affect any other systems of the body. This is probably the shortest Clincal Features section on the website.

Bone mineral density (BMD)

BMD is pretty much what is says on the tin - how dense your bones are. The less dense, the more likely you are to have a fracture (generally - really dense bones fracture too, but that's another story). Your BMD is given a T-score and this is how diagnoses of osteoporosis are made:

The WHO/International Osteoporosis Foundation criteria are:

• Normal - T score ≥ -1
• Low bone mass (osteopenia) - T score between -1 and -2.5
• Osteoporosis - T score ≤ -2.5
• Severe osteoporosis - T score ≤ -2.5 + fracture

BMD is assessed using a dual X-ray absorprimetry (DXA) scan which is basically a really badass way of looking how dense bones are. The T score is basically the number of standard deviations away from the lower limit of what is considered normal. Don't worry about it too much - just remember that T scores are negative.

Bloods

• FBC - evidence of chronic disease
• ESR - evidence of chronic disease
• U+Es - renal failure
• LFTs - ↑alk phos (rheumatoid arthritis)
• TFTs - hypothryoidism may have an effect (not sure about that one though)
• Parathyroid hormone - hyperparathyroidism
• Serum calcium - calcium is essential to bone formation
• Serum immunoglobulins - don't know why
• Testosterone/gonadotrophins - hypogonadism

Urinalysis

Bence-Jones proteins for myeloma.

Management

This differs depending on the result of the DXA scan

• Normal (T score ≥ -1)
  • Lifestyle advice - regular exercise, stop smoking and avoid excessive alcohol
• Osteopenia (T score -1 to -2.5)
  • Lifestyle advice as aboe
  • Offer treatment if previous fracture
• Osteoporosis (T score ≤ -2.5)
  • Lifestyle advice as above
  • Offer treatment

Treatment

Bisphosphonates are the mainstay treatment of osteoporosis. If you remember nothing else about osteoporosis treatment, remember "bisphophonates". They inhibit osteoclasts (bone destroying cells) and so decreas resorption. The ones used are risedronate and alendronate (or alendronic acid). Etidronate is an older drug but is less effective. Bisphosphonates should be prescribed alongside Calcium/Vitamin D e.g. Calcichew (vitamin D can be prescribed on its own). Side-effects of bisphosphonates: oesophagitis (can be prevented by sitting upright after ingestion for 30-60 mins).

Other treatments include: strontium ranelate (a dual action bone agents or DABA); raloxifene (a selective oestrogen receptor modulator or SERM); and parathyroid hormone peptides which are used where bisphosphonates are not tolerated.

Prognosis

Bono from U2 wrote the song "Elevation" about elevating osteoporotic patient's BMD. Ask him what the prognosis for osteoporotic patients.