calcium and phosphate metabolism

Question 1

describe osteoporosis

Answer 1

loss of bone mass

causes:
endocrine 
malignancy 
drug-induced
renal disease 
nutritional 
age

Question 2

describe diagnosis of osteoporosis

Answer 2

measurement of bone mineral density

dual-energy-x-ray absorptiometry

T score = number of SDs below average for young adult at peak bone density

Z score = matched to age and or group

Question 3

endocrine causes of osteoporosis

Answer 3

hypogonadism = notably any cause of oestrogen deficiency

excess glucocorticoids = endogenous or exogenous

hyperparathyroidism

hyperthyroidism

Question 4

treatments for osteoporosis

Answer 4

ensure adequate calcium and vit D intake, appropriate exercise

postmenopausal: HRT - effects well established but safety of long term treatment was questioned in early 2000s

bisphosphonates = inhibit function of osteoclasts: risedronate, alendronate

PTH analogues

denosumab = human monoclonal antibody against RANK ligand

romosozumab = human monoclonal antibody against sclerostin

Question 5

osteomalacia

Answer 5

loss of bone mineralization

signs and symptoms:
- permanent deformities in bone (rickets)

• diffuse aches and pains

chronic fatigue
weak bones
low ca, Pi
elevated alkaline phosphatase

PTH may be elevated

Question 6

cause of osteomalacia

Answer 6

vitamin D deficiency

mutations leading to errors in vit D metabolism

hypophosphatemia

treatment most commonly involves ensuring adequate Vit d and Ca

Question 7

FGF-23 = hormone secreted by osteocytes

Answer 7

phosphate balance = increases renal excretion

disorders:

• oncogenic osteomalacia
• x linked hypophophatemic rickets
• autosomal dominant hypophophatemic rickets

Question 8

renal osteodystrophy

Answer 8

spectrum of conditions associated with bone lesions in renal failure

• impaired pi excretion
• high plasma Pi
• low plasma Ca
• PTH rises
• excess bone resorption
• may be augmented by acidosis
• PTH rises