What is osteoporosis?

It is a disease characterized by low bone mass and microarchitectural deterioration of bone tissue, leading to enhanced bone fragility and a consequent increase in the risk of fracture.

The Wolrd Health Organization (WHO) defines osteoporosis as a bone density that falls 2.5 standard deviations (sd) below the mean for young healthy adults of the same sex. It is also referred to as a t-score of –2.5 or less.

Osteoporosis is a painless condition that is usually diagnosed on screening. However, subtle patients that may be unnoticed include a stooped posture and loss of height.

Many times patients are diagnosed when they have a fracture following minor trauma.

Bone remodeling – osteoblasts and osteoclasts

What factors might lead to porous bones (osteoporosis)?

Risk factors for the development of osteoporosis include:

Advanced age and immobility are the major risk factors for osteoporosis. Other risk factors include:

Causes of Osteoporosis:

Most of the factors mentioned above result in osteoporosis. The following medical conditions should be investigated for in a patient with osteoporosis:

Classification of Osteoporosis:

Osteoporosis can be classified on the basis of the etiology as:

  • Primary Osteoporosis
  • Postmenopausal Osteoporosis (type I)
  • Senile Osteoporosis (type II)
  • Secondary Osteoporosis due to an underlying disease (such as autoimmune rheumatic diseases, kidney & liver diseases, and hyperparathyroidism), deficiency states (such as calcium and vitamin D deficiency), or drugs (such as antiandrogens and corticosteroids).

How to investigate Osteoporosis patients?

Investigations aim to:

  • Diagnose and assess the severity of osteoporosis
  • Evaluate the underlying cause especially in osteoporosis at a younger age.

For the diagnosis of osteoporosis, the best test if Dual-energy x-ray absorptiometry (DEXA scan).

Other tests that may be used to measure bone density include:

  • Ultrasound,
  • Peripheral dual-energy x-ray absorptiometry (pDXA),
  • X-ray absorptiometry,
  • Peripheral quantitative computed tomography (pQCT) of the heel, radius, or hand.
Patients should be investigated for secondary causes:

Investigations to exclude secondary causes should be guided by the clinical features.

Usual investigations include:

  • Complete blood cell count
  • ESR
  • Blood sugars
  • Electrolytes
  • Creatinine
  • Blood urea nitrogen
  • Calcium
  • Phosphorus
  • Total proteins
  • Serum albumin
  • Alkaline phosphatase
  • Liver enzymes
  • 24-hour urine calcium
  • Serum protein electrophoresis
  • Vitamin D levels
  • Intact parathyroid hormones
  • Thyroid function tests

What is a Dexa scan and how to measure bone mineral density?

Bone mineral density is measured by performing a Dexa scan. It is a useful tool for identifying patients with osteoporosis, assess the severity, and the risks of fracture.

It is a useful screening test and is used to monitor the treatment response.

What do the different Bone mineral density scores signify?

A T-score represents the number of SDS (standard deviations) from the normal young-adult mean values.

T-scores are also used for diagnostic classification in postmenopausal women.

Z-Score represents the number of SDS from the normal mean value for age, race or ethnicity, and sex-matched.

Z-scores are recommended for premenopausal women, with a z-score –2.0 or lower defined as below the expected range for age and greater than –2.0 as within the expected range for age.

The WHO criteria for the diagnosis of osteoporosis based on Bone Mineral Density:

  • Normal:
    • Bone mineral density measurement: A bone mineral density within 1 SD of the mean bone density for young adult women
    • T score: T-score ≥ –1
  • low bone mass (osteopenia):
    • Bone mineral density measurement:bmd 1–2.5 sd below the mean for young adult women
    • T score: T-score between –1 and –2.5
  • osteoporosis
    • Bone mineral density measurement: Bone mineral density ≥2.5 sd below the normal mean for young adult women
    • T score: T-score ≤ –2.5
  • severe or “established” osteoporosis
    • Bone mineral density measurement: Bone mineral density ≥2.5 sd below the normal mean for young adult women in a patient who has already experienced ≥1 fracture
    • T score: T-score ≤ –2.5 (with fragility fracture[s])

Indications for bone density testing

  • Women age 65 and older, men aged 70 years and older regardless of clinical risk
    factors.
  • younger postmenopausal women, women in the menopausal transition and men aged
    50 – 69 with clinical risk factors for fracture

    • a history of fracture of the wrist, hip, spine
    • family history of osteoporotic fracture
    • low body mass (less than 57.6 kg)
    • current use of cigarettes
    • excessive use of alcohol
    • loss of height, thoracic kyphosis
  • adults with a condition (e.g., rheumatoid arthritis, chronic kidney disease, eating disorders, malabsorption or osteomalacia.

Indications for DEXA scanning:

Individuals of any age with findings suggestive of demineralization or fragility fractures on imaging studies such as radiographs, CT scans, or Magnetic resonance imaging.

Individuals with an endocrine disorder (eg, hyperparathyroidism, hyperthyroidism, or Cushing’s syndrome).

Individuals receiving glucocorticoid therapy for more than 3 months (a daily dose of ≥5 mg prednisone or equivalent for≥3 months).

Assess the effectiveness of osteoporosis drug therapy.

Follow up medical conditions associated with abnormal bone mineral density.

Dual-energy x-ray absorptiometry (DXA)

It is the best current test to measure BMD. This technique is rapid and takes only 3 to 7 minutes.

It delivers a radiation dose that is so low as to be equivalent to approximately 5% of the radiation dose of one chest radiograph.

Measure BMD at specific sites: the lumbar spine, hip, and distal forearm.

Contraindication’s DEXA scan:

Dexa scan is not recommended in the following group of patients:

  • Pregnancy
  • In individuals who have recently had gastrointestinal contrast, BMD should be delayed by at least 72 hours as these tests can affect the results of the scan.
  • Obese individuals weighing more than 250 pounds or 114 kg cannot be accommodated in the central DEXA units.
  • Severe degenerative changes or fracture deformity in the measurement area.
  • Implants, hardware, devices, or other foreign material in the measurement area.
  • The patient’s inability to attain the correct position.

Fracture risk assessment tool (FRAX):

It is a diagnostic tool used to evaluate the 10-year probability of bone fracture risk.

A ten-year fracture risk of >3% at the hip or >20% total fracture risk is generally considered an indication to begin pharmacologic therapy.

It helps to identify the individual who needs treatment.

It is an internationally organized and validated score and recommended by most authorities.

Indications for FRAX score assessment:

  • All postmenopausal women or men 50 years of age and older
  • People with low bone density (osteopenia)
  • People who have not taken an osteoporosis medicine.
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Musaddiq Islam
Musaddiq Islam
2 years ago

Beautifully written article. Especially the radiation dose of DEXW scan was unknown to me before.