Advantages And Disadvantages Of Osteoporosis Diagnostic And Treatment Techniques

Introduction

Osteoporosis is a disease of the skeletal system, in which the bone strength is negatively affected to various degrees, resulting in a higher probability of pathological fractures (Nih Consensus Development Panel on Osteoporosis Prevention & Therapy, 2001). Bone strength highly depends on the concentration of minerals in the bone tissue and, therefore, the main measure of bone strength is bone mineral density (BMD) (Nguyen, Pocock, & Eisman, 2000). BMD is measured as grams of mineral per unit of bone tissue volume or area. Another parameter, bone quality, represents an overall structure of the bone, mineralization and turnover of the bone tissue.

The dual-energy x-ray absorptiometry (DEXA) scan has become a standard for determining the BMD using the T score for classification purposes. A T score ranging from -2.5 to -1 is classified as osteopenia, whereas a T score below -2.5 is considered as an indicator of osteoporosis (Sheu & Diamond, 2016). However, this approach is not applicable to all patients. There are patients who present normal levels of BMD and multiple fractures due to bone fragility (Kanis, 2002). Because of these limitations, World Health Organization (WHO) has provided the Fracture Risk Assessment Tool (FRAX), which considers risk factors, as well as BMD of the femoral neck, in order to enable more precise and more accurate diagnosis of osteoporosis (Kanis et al., 2017).

Epidemiology and pathophysiology of osteoporosis

Osteoporosis contributes greatly to morbidity and mortality worldwide, predominantly affecting older population and female gender. Results of epidemiological studies have shown that half of all women and one fifth of men older than 50 years are going to suffer from bone fractures due to increased bone tissue fragility. Moreover, people with hip fractures have a mortality rate of 20% (Pouresmaeili, Kamalidehghan, Kamarehei, & Goh, 2018). Vertebral fractures are even more prevalent, but many of these patients do not seek medical examination due to less severe symptoms.

Bone tissue remodeling is a lifelong, continuous process in which there must be a balance between the activity of osteoblasts – responsible for bone formation – and osteoclasts – responsible for bone resorption. There are many factors that can disrupt this balance, such as reduced levels of estrogen in postmenopausal women. Estrogen is responsible for continuous remodeling of the bone tissue, and its lack can increase the activity of osteoclasts, leading to a reduction in bone strength and structure (Ji & Yu, 2015). These cases are classified as primary osteoporosis type 1. Primary osteoporosis type 2, also called senile osteoporosis, is caused by the aging of cortical and trabecular bones (Cosman et al., 2014). There are also secondary causes of osteoporosis, such as secondary hyperparathyroidism, due to renal failure, and vitamin D deficiency (Cunningham, Locatelli, & Rodriguez, 2011).

Clinical presentation of osteoporosis

Osteoporosis is often asymptomatic until the fractures start to appear. As said above, due to the neglecting of vertebral fractures, diagnosis can be significantly delayed. Fragility fractures may produce chronic pain, permanent disability, and even death. Clinicians may notice decreased height, dorsal kyphosis, poor balance, and impaired proprioception in patients with vertebral fractures (Sozen, Ozisik, & Basaran, 2017).

Diagnostic imaging pathway in osteoporosis

The diagnostic imaging pathway has been designed for patients with suspected osteoporosis, in order to adjust the examination process so that they can receive the highest possible benefit and, at the same time, avoid the application of unnecessary, possibly harmful imaging techniques. As the pathway diagram shows in detail (Appendix 1), there are three important aspects which should indicate the need to proceed with the pathway: an immediate history of a minimal trauma fracture; biochemical markers of osteopenia or osteoporosis; and indications for a DEXA scan. By following the pathway, it becomes obvious that DEXA scan is the preferable imaging technique and the gold standard for determining BMD (Nanes & Kallen, 2014). This has been confirmed by many studies (Punda & Grazio, 2014; Smith & Shoukri, 2000; Tu et al., 2018). Additionally, following the pathway can provide detailed information regarding further steps in patient evaluation and treatment.

Advantages and limitations of the most commonly used imaging techniques in osteoporosis

DEXA is a standardized and easy to use technique, with minimal exposure to radiation, ranging from 1 to 50 μSv, during the assessment of vertebral fragility fractures. It is also very accurate, with a precision error of 2.5% for femur neck, 1.9% for lumbar spine, and 1.8% for total hip (Kim & Yang, 2014). Two x-ray beams are used, one with a maximum kilovoltage of 70 keV, and the other usually between 30 and 50 keV. This enables the subtraction of non-bone tissue and makes DEXA perfect for BMD measurements in the femur head area, lumbar spine and distal radius area (Link, 2012). DEXA also gives important information in the form of Z scores and T scores, which represent standard deviations of different types. The Z score is a standard deviation compared to the same age group and the T score is matched with a population of young healthy adults (Link, 2012).

There are some significant disadvantages of DEXA, which should be taken into account. Since DEXA measures the density in two-dimensional space, it means that the BMD is only measured by the unit of surface and not volume. BMD is related to bone size/length so, in individuals with smaller bones, DEXA can give false positive results concerning the increased risk of fragility fractures (Garg & Kharb, 2013). Furthermore, degenerative diseases of vertebral bone tissue are often presented in radiology with increased bone density. Calcifications of the surrounding structures, such as aorta, may also lead to misinterpretation of DEXA results. This may be misleading, while performing DEXA to establish the diagnosis of osteopenia/osteoporosis, giving false negative results (Rand et al., 1997). Therefore, it is important to exclude all the possible sources of doubt while performing DEXA or, if not possible, to proceed with other imaging techniques, which can provide more relevant details about the pathology.

Other radiological techniques

In cases when DEXA cannot offer enough relevant information about BMD, or if there is a need for a more detailed examination, there are other radiological techniques that can be used. Although quantitative computer tomography (CT) is not considered a gold standard for diagnosing osteopenia and osteoporosis, it still has some advantages over DEXA. Quantitative CT measures bone density in three-dimensional space, in a volumetric manner, and therefore, its results do not depend on the patient’s bone size (Link, 2012). It also provides trabecular measurements of the bone structure, which is not possible with DEXA.

Studies have also shown that quantitative CT measurements give more accurate results than DEXA in obese individuals, because a thick layer of fat tissue can increase the BMD value measured by DEXA to some extent (Yu, Thomas, Brown, & Finkelstein, 2012). This is, however, a controversial topic, and not all authors agree with that theory. Of course, the main disadvantage of CT is a higher radiation exposure. Consequently, there are not enough studies to confirm the absolute suitability of quantitative CT for determining the changes in BMD. Quantitative CT is, therefore, considered as a complementary diagnostic tool in cases in which DEXA experiences its well-known pitfalls.

Other radiological techniques used for the diagnosis of osteoporosis have a very limited ability in providing consistent results and they are often used in primary care, where DEXA or quantitative CT are not available. These include imaging of peripheral structures, such as digital x-ray radiogrammetry, peripheral DXA and peripheral quantitative CT. These methods are not recommended to use, as they often provide a very limited amount of information, frequently inconsistent and not relevant enough (Fogelman & Blake, 2005).

Treatment options and outcomes in osteoporosis patients

Treatment of patients with osteoporosis consists of two parts: pharmacological and nonpharmacological treatment. Nonpharmacological management of osteoporosis consists of calcium and vitamin D supplementation, controlled physical activity and quitting bad lifestyle habits, such as smoking, alcohol and caffeine. It is also important that people with osteoporosis get educated on how to prevent falls and injuries that can cause fragile bone fractures (Cosman et al., 2014).

The Institute of Medicine (IOM) recommends a maximum daily intake of calcium supplements of 1,000 mg per day for men 50 to 70 years of age. For women older than 50 years, it should not exceed 1,200 mg and the same rule applies for men older than 70 years (Ross et al., 2011). Some authors accentuate the risk of developing renal lithiasis due to long term calcium supplementation. On the other hand, scientists believe that dietary calcium can lower the risk of renal lithiasis development. So, the general recommendations are to increase dietary calcium intake before applying calcium supplementation.

It is a known fact that vitamin D is very important for calcium absorption and bone health. The IOM recommends 600 IU per day for men and women 51 to 70 years of age and 800 IU per day for men and women older than 70 years (Ross et al., 2011). Vitamin D supplementation is currently receiving great attention. Despite the claims that it can reduce the risk of fragility fractures, recent studies have shown that vitamin D supplementation, especially in high doses, may be the cause of more frequent falls. Low to moderate daily doses of vitamin D are considered perfectly safe, though (Chung, Lee, Terasawa, Lau, & Trikalinos, 2011).

The main purpose of pharmacological therapy is to reduce the risk of fractures. Medications to treat osteoporosis have either antiresorptive or anabolic activity. The most common antiresorptive medications used are bisphosphonates, estrogen agonist/antagonists [EAAs], estrogens, calcitonin and denosumab, while the most common anabolic drug is teriparatide. Antiresorptive medications lower the rate of bone resorption, while anabolic drugs stimulate bone regeneration. Some of the drugs used in the medications for the treatment of osteoporosis are not approved by the Food and Drug Administration (FDA) for this specific indication. According to AACE/ACE recommendations, people at high risk of fracture should start with medications from bisphosphonate group (Qaseem, Forciea, McLean, Denberg, & Clinical Guidelines Committee of the American College of, 2017).

The outcome of osteoporosis depends on many factors, such as the severity of the disease, compliance with the therapy regimens and lifestyle changes. After having a fragility fracture, the outcome of the disease becomes even more uncertain. Successful recovery depends on bone healing process, existing comorbidities, and the general awareness that patients need to be careful, because each new fracture slows down the recovery, prolongs morbidity and increases mortality.

Conclusion

In conclusion, the diagnosis of osteoporosis is often straightforward, but in some cases can be difficult due to limitations of current diagnostic methods. Luckily, there is the diagnostic imaging pathway which can help health care professionals to make appropriate choices, depending on the clinical presentation of the disease. The golden standard for diagnosing osteoporosis by determining decreased BMD is still DEXA. In some cases, quantitative CT can be used to help achieve the right diagnosis. The treatment can be nonpharmacological, such as vitamin D supplementation, controlled physical activity and calcium supplements, as well as pharmacological, with bisphosphonates as the first line. Although dependent on many factors, the outcome of osteoporosis can be very promising if all the recommendations are taken.