Metabolic bone disease Flashcards
What is the action of parathyroid hormone (PTH)?
PTH increases the concentration of calcium in the plasma and reduces the plasma phosphate. PTH also increases the tubular reabsorption of calcium in the kidneys
Where is PTH secreted from?
The chief cells of the parathyroid glands
What is the action of calcitonin?
Acts to decrease concentration of calcium in the blood. (Skeleton preserving action.)
Where is calcitonin secreted from?
The parafollicular (c cells) of the thyroid gland
Calcitriol is derived from vitamin D by successive hydroxylation in which organs?
Liver and kidney
What is the WHO definition of osteoporosis?
A bone density more than 2.5 standard deviations below the young adult mean value (T-score less than -2.5).
A bone density T-score of of -1.0 to -2.5 = osteopenia
What would you expect to be elevated in the blood test of someone with Paget’s disease?
Alkaline phosphatase
Describe x-ray changes seen in Paget’s disease of the bone
The x-ray would show localised enlargement of bone, patchy cortical thickening, deformity, sclerosis and osteolysis indicated by radiolucent areas
What is Paget’s disease of the bone?
Paget’s disease of the bone is characterised by increased bone turnover with associated increased numbers or osteoblasts and osteoclasts. The bone undergoes remodelling, with the structure of the new bone being disorganised, bulky and mechanically weaker.
What are Bence-Jones proteins in the urine indicative of?
Multiple myeloma
Name two bisphosphonate drugs used to treat osteoporosis
Alendronate and risedronate
Why must the patient stand for 30 minutes after taking a bisphosphonate?
To reduce reflux. Bisphosphonates can cause oesophagitis if administration instructions are not adhered to.
Other instructions = take on an empty stomach and with water only to improve absorption
What class of drug is Raloxifene? How does it work? What are the indications?
Raloxifene belongs to a class of drugs called: selective estrogen receptor modulators (SERMs). It exerts estrogen-like effects on the skeleton and reduce the risk of vertebral fractures (it also protects against breast cancer - strangely!) They are recommended by NICE as an alternative to bisphosphonates in postmenopausal women who sustain a low trauma fracture but should be avoided immediately after the menopause, as it tends to increase the severity of hot flushes.
What is Strontium used for? How does it work?
Strontium is a useful alternative in patients who are intolerant of bisphosphonates. It has a dual effect in both stimulating osteoblast activity and suppressing osteoclasts; and has been found to reduce the risk of both vertebral and nonvertebral fractures.
What is Teriparatide?
Recombinant parathyroid hormone - used for the treatment of refractory osteoporosis.
(It may seem paradoxical that PTH is given to increase bone mineral density, given that PTH stimulates osteoclasts, causing resorption of bone. However, it has been shown that by giving the drug in daily pulses, there is an increase in new bone formation, bone mineral density and improvement in trabecular architecture)
