Osteoporosis Definitions
An international consensus definition of osteoporosis states: "Osteoporosis is a systemic skeletal disease characterised by low bone mass and micro architectural deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fracture" (AM J Med 1993; 94:646).
Normal Bone vs. Osteoporotic Bone Histology
The most common reasons for osteoporosis in older women are:
- the effect of the menopause leading to rapid bone breakdown,
- impaired intake and absorption of calcium and vitamin D leading to increased age related bone loss, and
- decreased physical activity with increasing age
Bone loss in men is in part due to the causes outlined in b) and c) above.
Secondary Osteoporosis Secondary osteoporosis is a reduced bone mass caused by conditions other than age.
Causes of Secondary Osteoporosis
| Endocrine or Metabolic | Nutritional | Drug Usage | Other |
| Acromegaly | Alcoholism | Azathioprine | Ankylosing spondylitis |
| Anorexia nervosa | Calcium deficiency | Cyclosporin | Cholestatic liver disease |
| Diabetes type I & II | Chronic liver disease | Excess thyroid medication | Chronic obstructive pulmonary disease |
| Hyperadrenalism | Gastric and small gut resection | Glucocorticosteroids | Crohn’s Disease |
| Hyperprolactinemia | Vitamin D deficiency | Heparin | Hypercalciuria |
| Hyperparpathyroidism | Malabsorption | Methotrexate | Immobilisation |
| Hypophosphatasia | Phenobarbital | Mastocytosis | |
| Porphyria | Phenytoin carbamazepine | Multiple Myeloma | |
| Thyrotoxicosis | Vitamin D toxicity | Organ transplant | |
| Renal tubular acidosis | |||
| Rheumatoid arthritis | |||
| Thalassemia | |||
| Ulcerative colitis |
The World Health Organisation has further defined osteoporosis according to the T-scores from a DEXA assessment for post menopausal women.
Normal bone mass is defined as any BMD that is greater than one standard deviation below the young adult mean.
(T-score > -1)
Reduced bone mass (osteopenia) is defined as any BMD between one and two and a half standard deviations below the young adult mean.
(-1.0 > T-score > -2.5)
Osteoporosis is defined as any BMD less than two and a half standard deviations below the young adult mean.
(T-score < -2.5)
[Refer to Appendix 4 for information on male osteoporosis]
