Osteoporosis classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Eiman Ghaffarpasand, M.D. [2]

Overview

Osteoporosis is classified based on etiology and severity of the disease. Osteoporosis may be divided into primary and secondary types, based on disease etiology. On the basis of disease severity, it can be classified as osteopenia, osteoporosis, and severe osteoporosis. Osteoporosis is rare in children and adolescents. Secondary osteoporosis results from various comorbidities or the use of certain medications, whereas, idiopathic osteoporosis has no known cause.

Classification

Osteoporosis may be classified based on etiology and severity of the disease.

Osteoporosis

Based on Severity

Based on Etiology

Children

Adults

Children, Adolescents, and Adults

Z-score measurement

T-score measurement

Bone loss due to other diseases?

Z-score > -2.0 without fracture history

Z-score < -2.0 and significant fracture history (2 or more long bone fractures before 10 years of age or 3 or more long bone fractures before 19 years of age) OR One or more vertebral fractures occurring in the absence of local disease or high-energy trauma

-1 > T-score > -2.5

T-score ≤ -2.5

T-score ≤ -2.5 plus history of fracture

No

Yes

Normal

Osteoporosis

Osteopenia

Osteoporosis

Severe osteoporosis

Primary osteoporosis

Secondary osteoporosis

Osteoporosis classification based on disease etiology

On the basis of etiology, osteoporosis can be classified into:

Primary Osteoporosis

Primary osteoporosis develops as a result of aging or menopause-related bone demineralization. In patients with primary osteoporosis, the bone density decreases as the age progresses.

Secondary Osteoporosis

Secondary osteoporosis results from more severe loss of bone mass due to pathologies associated with immobilization, medications (iatrogenic), endocrine dysfunction, cancer, and chronic kidney disease.

Osteoporosis classification based on disease severity

Osteoporosis may be classified based on the bone marrow density (BMD). The patients are classified according to the site and method of measurements. The used equipment and reference group of people may also be helpful in classification of osteoporosis. The major value used in the classification of osteoporosis is T-score. T-score may be defined as "patient measured BMD value minus the reference BMD value (sex-matched and with a preference for youth) divided by the reference standard deviation (SD) (sex-matched and with a preference for youth)".

The classification of osteoporosis on the basis of BMD measured T-score is as follows:

• T-score less than -1 and more than -2.5: Osteopenia
• T-score equal to or less than -2.5: Osteoporosis
• T-score equal to or less than -2.5 with history of fracture: Severe osteoporosis

The exclusive utilization of T-score and comparing the reference normative data of people aged 20-29 years, as world health organization (WHO) criteria, is very inconsistent. Compared to other classification systems, it is better to standardize the normative data, by including older people and individuals with other findings including BMD measurement at multiple sites, in order to obtain a comprehensive classification system.

Osteoporosis in children

• Bone mass, as measured by DEXA, is reported as bone mineral content (BMC) (g) or areal BMD (g/cm2). These values are compared to reference values from individuals of similar age, sex, and ethnicity to calculate the Z-score, the number of SDs from the expected mean. Abundant pediatric reference data is now available for children and teenagers but not for infants.
• It is essential to select norms collected by using equipment from the same manufacturer as that used for the patient because of systematic differences in software. Peak bone mass is achieved in the second or third decade, depending on the skeletal site. Therefore, T-scores (which compare the patient’s BMD with that of a healthy young adult) should not be used before 20 years of age.
• The appropriate interpretation of DEXA results may require more than the calculation of Z-scores.
• Children with chronic illness often have delayed growth and pubertal development, factors that contribute to a low bone mass for age or sex. BMD, as measured by DEXA, corrects bone mineral for the area (height and width) but not for the volume (height, width, and thickness) of bone. For this reason, if 2 individuals with identical “true” volumetric bone density are compared, the shorter person will have a lower BMD than the taller one. Similarly, a child with delayed puberty will not have had the gains in bone size, geometry, and density that occur with sex steroid exposure.
• Controversy persists about the optimal method to adjust for variations in bone size, body composition, and maturity as well as the criteria by which the “best method” is defined; ideally, the adjustment method would prove to be a stronger predictor of fracture.
• The Pediatric Development Conference (PDC) guidelines recommend that BMD in children with delayed growth or puberty be adjusted for height or height age or compared with reference data with age, sex, and height-specific Z-scores.
• The terms “osteopenia” and “osteoporosis” are used in older adults to describe degree of deficits (lesser or greater) in bone mass. These terms should not be used to describe densitometry findings in pediatric patients. Instead, a BMC or BMD Z-score that is > 2 SDs below expected (< - 2.0) is referred to as “low for age”.
• The following criteria for osteoporosis in a pediatric patient were agreed on in the 2013 PDC guidelines:
  • One or more vertebral fractures occurring in the absence of local disease or high-energy trauma (measuring BMD can add to the assessment of these patients but is not required as a diagnostic criterion);
  • Low bone density (BMC or areal BMD Z-scores < - 2.0) and a significant fracture history (2 or more long bone fractures before 10 years of age or 3 or more long bone fractures before 19 years of age).
  • Lastly, it is important to recognize that there are certain diseases in pediatric population (e.g., end-stage renal disease and spinal vertebral fractures) in which DEXA does not accurately reflect fracture risk or bone health.

Juvenile Osteoporosis (JO)

• Osteoporosis in children and adolescents is rare. Usually, it is due to some comorbidities or medications (secondary osteoporosis). Surprisingly, no significant causes have been found for rare cases (idiopathic osteoporosis).
• Irrespective of the cause, juvenile osteoporosis can be a significant problem because it occurs during the child’s prime bone-building years. From birth through young adulthood, children steadily accumulate bone mass, which peaks, sometimes, before age 30. The greater their peak bone mass, the lower their risk for osteoporosis later in life. After people reach their mid-thirties, bone mass typically begins to decline very slowly at first but the decline accelerates in their fifties and sixties. The lifestyle choices, especially the amount of calcium in the diet and the level of physical activity influence the development of peak bone mass and the rate at which bone is lost later in life.

Secondary Osteoporosis

• As the primary condition, juvenile idiopathic arthritis (also known as juvenile rheumatoid arthritis) provides a good illustration of the possible causes of secondary osteoporosis. In some cases, the disease process itself can cause osteoporosis.
• In other cases, the medication used to treat the primary disorder may reduce bone mass. For example, drugs such as prednisone used to treat severe cases of juvenile idiopathic arthritis, negatively affect bone mass.
• Finally, some behaviors associated with the primary disorder may lead to bone loss or reduction in bone formation. For example, a child with juvenile idiopathic arthritis may avoid physical activity, which is necessary for formation and maintainence bone mass, because it may aggravate his or her condition or cause pain.
• For children with secondary osteoporosis, the best course of action is to identify and treat the underlying disorder. In the case of medication-induced juvenile osteoporosis, it is best to treat the primary disorder with the lowest effective dose of the osteoporosis-inducing medication. Like all children, those with secondary osteoporosis also need a diet rich in calcium and vitamin D and as much physical activity as possible given the limitations of the primary disorder.

Idiopathic Juvenile Osteoporosis

• Idiopathic juvenile osteoporosis (IJO) is a primary condition with no known cause. It is diagnosed after other causes of juvenile osteoporosis have been excluded. This rare form of osteoporosis typically occurs just before the onset of puberty in previously healthy children. The average age at onset is 7 years, with a range of 1 to 13 years. Most of the children experience complete recovery of bone.

• The first sign of IJO is usually pain in the lower back, hips, and feet, often accompanied by difficulty walking. Knee, ankle pain and fractures of the lower extremities may also occur. Physical malformations include kyphosis, loss of height, a sunken chest, or a limp. These physical malformations are sometimes reversible after IJO has run its course.

• X-rays of children with IJO often show low bone density, fractures of weight-bearing bones, and collapsed or deformed vertebrae. However, conventional X-rays may not be able to detect osteoporosis until significant bone mass has occurred. Newer methods such as dual energy x-ray absorptiometry (DXA), and quantitative computed tomography (QCT ) allow for earlier and more accurate diagnosis of low bone mass.

• There is no established medical or surgical therapy for juvenile osteoporosis. In some cases, no treatment may be needed because the condition usually goes away spontaneously. However, early diagnosis of juvenile osteoporosis is important so that steps can be taken to protect the child’s spine and other bones from fracture until remission occurs. These steps may include physical therapy, use of crutches, avoiding unsafe weight-bearing activities, and other supportive care. A well-balanced diet rich in calcium and vitamin D is also important. In severe, long-lasting cases of juvenile osteoporosis, bisphosphonates, approved by the Food and Drug Administration for the treatment of osteoporosis in adults, have been given to children experimentally.
• Most children with IJO experience complete recovery of bone tissue. Although growth may be somewhat impaired during the acute phase of the disorder, normal growth resumes and catch-up growth often occurs afterward. Unfortunately, in some cases, IJO can result in permanent disability such as kyphoscoliosis or collapse of the rib cage.

References

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