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 may be classified into several subtypes based on disease origin and disease severity. Osteoporosis is divided into primary and secondary diseases upon classification based on disease etiology. While, it becomes divided to osteopenia, osteoporosis, and severe osteoporosis, upon classification based on disease severity. Osteoporosis in children and adolescents is divided to idiopathic osteoporosis (with no significant cause) and secondary osteoporosis (due to some comorbidities or specific medications).
Classification
Osteoporosis may be classified into several subtypes based on disease origin, and disease severity.
| Osteoporosis classifications | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Based on Severity | Based on Etiology | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Children and Adolescents | 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 origin
One of the major classification systems for osteoporosis is based on the origin disease come from; including:
- Primary osteoporosis: Normal process of life, through which the bone density becomes low, such as aging or postmenopausal osteoporosis.
- Secondary osteoporosis: Earlier, more severe form of bone mass loss due to some kind of pathology, such as immobilization, medication-induced (i.e., iatrogenic), endocrine dysfunction, cancer-related, and chronic kidney disease related osteoporosis.[1]
Osteoporosis classification based on disease severity
The main established classification system for osteoporosis is based on bone marrow density (BMD). The patients are classified upon the site and method of measurements; also the used equipment and reference group of people may play roles. Finally, the major value using for classification of osteoporosis is T-score. T-score would be defined as "patient measured BMD value minus the reference BMD value (sex-matched and preferably for youth) divided the reference standard deviation (SD) (sex-matched and preferably for youth)".[2]
The common classification of osteoporosis upon BMD measured T-score is as following:
- T-score less than -1 and more than -2.5 assumes as osteopenia
- T-score equal to or less than -2.5 assumes as osteoporosis
- T-score equal to or less than -2.5 with history of fracture assumes as severe osteoporosis
Lu and his colleagues have found that pure using of T-score and comparing to reference normative data 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, maybe referring to older people; and also complex the findings of multiple sites BMD measures, in order to obtain a better classification system.[2]
Osteoporosis in children and adolescents[3]
Bone mass, as measured by DEXA, is reported as BMC (g) or areal BMD (g/cm2). These values are compared to reference values from healthy youth of similar age, sex, and race/ethnicity to calculate the Z-score, the number of SDs from the expected mean. Abundant pediatric reference data are 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 lesser or greater deficits 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:[4]
- 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 pediatrics (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).
No matter what causes it, 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 sometime 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 acceleratesa in their fifties and sixties. Both heredity and 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, 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 building and maintaining bone mass, because it may aggravate his or her condition or cause pain.[5]
Disorders, Medications, and Behaviors That May Affect Bone Mass:
Primary Disorders
- Juvenile rheumatoid arthritis
- Diabetes
- Osteogenesis imperfecta
- Hyperthyroidism
- Hyperparathyroidism
- Cushing’s syndrome
- Malabsorption syndromes
- Anorexia nervosa
- Kidney disease
Medications
Behaviors
- Prolonged inactivity or immobility
- Inadequate nutrition (especially lack of calcium and vitamin D)
- Excessive exercise leading to amenorrhea
- Smoking
- Alcohol abuse
For children 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.[5]
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 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 and ankle pain and fractures of the lower extremities also may 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 misshapen vertebrae. However, conventional X-rays may not be able to detect osteoporosis until significant bone mass already has been lost. 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, using 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, some medications called 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 a 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.[5]
References
- ↑ Marcus, Robert (2013). Osteoporosis. Amsterdam: Elsevier/Academic Press. ISBN 9780124158535.
- ↑ 2.0 2.1 Lu Y, Genant HK, Shepherd J, Zhao S, Mathur A, Fuerst TP, Cummings SR (2001). "Classification of osteoporosis based on bone mineral densities". J. Bone Miner. Res. 16 (5): 901–10. doi:10.1359/jbmr.2001.16.5.901. PMID 11341335.
- ↑ Bachrach, L. K.; Gordon, C. M. (2016). "Bone Densitometry in Children and Adolescents". PEDIATRICS. 138 (4): e20162398–e20162398. doi:10.1542/peds.2016-2398. ISSN 0031-4005.
- ↑ Gordon CM, Leonard MB, Zemel BS (2014). "2013 Pediatric Position Development Conference: executive summary and reflections". J Clin Densitom. 17 (2): 219–24. doi:10.1016/j.jocd.2014.01.007. PMID 24657108.
- ↑ 5.0 5.1 5.2 "Juvenile Osteoporosis".