Osteoporosis

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Diagnosis and reasoning

This elderly lady has presented with acute back pain - an extremely common presentation in both primary care and emergency medicine. In most individuals, this is due to benign causes and resolves spontaneously; however, a wide variety of diseases may also present in this manner, and should be looked for. Important conditions to consider include spinal fractures, infections, neoplasia, metabolic derangements, inflammatory rheumatologic disorders, referred pain from other sources, Paget's disease, fibromyalgia, and psychogenic pain. A careful history and examination are key towards determining if she needs further evaluation in this regard. Reviewing her history, we see that the back pain commenced after a relatively trivial exertion, i.e. picking up a potted plant. This finding should be interpreted carefully, as many patients attribute unrelated events to the start of the back pain. Even if true, it is fairly equivocal as both benign pathologies (i.e. muscle sprains / spasms) and not-so-benign conditions (i.e. a pathological fracture) can present in this manner. The fact that the pain worsens upon exertion and is relieved by rest suggests a mechanical cause; however, the fact that it is persistent (i.e. present even at rest) is a point against this. Her examination proves to be much more productive, and brings to light two concerning findings: a loss of height of 2 inches (5 cm), and spinal point tenderness at the L1 vertebral level. After achieving their maximal height, women can lose up to 1.5 inches (3.8 cm) as part of the normal aging process (due to shrinkage of the intervertebral disks). A height loss of more than 1.5 inches is suggestive that vertebral fracture is present; in this patient, the presence of spinal point tenderness and the mechanical nature of the pain is further supportive of this. Further evaluation via imaging should be performed urgently; an x-ray shows a compression wedge fracture correlating with the area of tenderness, confirming the clinical suspicion. Her evaluation should not cease at this point - spinal fractures in the absence of significant trauma are distinctly unusual and should always raise suspicion of an underlying spinal pathology such as bone tumors (primary or metastatic), or osteoporosis; considering her age and gender, the latter two pathologies are of particular concern. A few basic investigations go a long way in screening for pathologies; note here the normal alkaline phosphatase (which is typically elevated in spinal metastasis) and normal ESR (which is usually elevated in multiple myeloma). Given her age and absence of hormone replacement therapy, osteoporosis is also a strong possibility; a dual-energy x-ray absorptiometry (DXA) scan along with vertebral fracture analysis (VFA) is the gold standard of evaluation of such patients. In this patient, the DXA T-score of -2.7 indicates a bone mineral density (BMD) which is 2.7 standard deviations below that of a normal 30-year old. This is diagnostic of osteoporosis. In addition, VFA confirms the presence of a compression wedge fracture (note that burst fractures can mimic wedge fractures in some cases - hence the importance of further evaluation), and additionally shows that the fracture is stable. Osteoporosis can be primary (ie. familial), or secondary in origin. Important secondary causes include hypocalcemia (secondary to vitamin D deficiency, malabsorption, etc) and hypophosphatemia; however, a simple screening test shows normal levels of each. Osteoporosis may also occur in individuals with underlying endocrinopathies (such as hyperthyroidism and diabetes mellitus) and renal or liver disease - she should undergo further screening in this regard. Her immediate management should include a short period of bed rest followed by gradual mobilization. Prolonged bed rest should be avoided, as this will just hasten bone loss. As vertebral compression fractures are flexion compression injuries, a hyperextension brace will aid in the management; these braces are usually beneficial for the first few months, until the pain resolves. Spinal fixation is unnecessary, as the fracture is stable; NSAIDs should be avoided in patients with healing fractures (particularly during the immediate and early inflammatory phases of healing) because it can impair recovery. Bisphosphonate therapy should also be commenced, as this will suppress osteoclast-mediated bone resorption and reduce the rate of reduction of BMD.


Discussion

Osteoporosis is the most common metabolic bone disease, affecting approximately 8 million women and 2 million men in the United States; it is estimated that 1 in 2 women and 1 in 4 men aged 50 years and older will have an osteoporosis-related fracture in their remaining lifetime. Osteoporosis is characterized by low bone mass and structural deterioration of bone tissue, leading to an increased risk of fractures; bone loss occurs when the bone remodelling balance is altered, resulting in greater bone removal than replacement. Primary osteoporosis is classified into juvenile osteoporosis and idiopathic osteoporosis; the latter is further subdivided into postmenopausal (type I) and age-associated or senile (type II) osteoporosis. Secondary osteoporosis may occur due to chronic medical and systemic diseases (COPD, rheumatoid arthritis, multiple myeloma, Inflammatory bowel diseases), endocrine and metabolic disorders (hyperparathyroidism, hyperthyroidism, Cushing's syndrome, Type 1 Diabetes Mellitus), drugs (steroids) and nutritional factors (alcoholism, vitamin D deficiency, etc). The most common osteoporotic fractures are those of the vertebrae, proximal femur and distal forearm. Once a fracture is detected, the diagnosis of osteoporosis can be achieved via dual-energy x-ray absorptiometry (DXA) measurements of the hip and spine; the dose of radiation involved is trivial. The World Health Organization (WHO) defines osteoporosis as a spinal or hip bone mineral density (BMD) of 2.5 standard deviations or more below the mean for healthy, young women (T-score of −2.5 or below) as measured by DXA. Osteopenia is defined as a spinal or hip BMD between 1 and 2.5 standard deviations below the mean. Note that DXA is also useful for estimation of the risk of future fractures, and for monitoring patients via serial assessments; the WHO Fracture Risk Assessment Tool (FRAX) can be used to calculate the 10-year probability of a hip fracture and the 10-year probability of a major osteoporotic fracture. VFA imaging of the thoracic and lumbar spine should be considered at the time of BMD assessment, as the presence of a vertebral fracture not previously identified may influence clinical management of the patient. In patients in whom a specific secondary, treatable cause of osteoporosis is being considered, investigations should be performed as appropriate (i.e. a full blood count for bone marrow malignancies and malabsorption; serum protein electrophoresis for multiple myeloma; TSH for hyperthyroidism; 25-hydroxyvitamin D levels for Vitamin D deficiency; and liver and renal functions for disease of the respective organs). Osteoporosis is preventable and treatable, but because there are no warning signs prior to a fracture, most individuals are not diagnosed during the early stages of the disease. Thus screening for osteoporosis is recommended in women who are 65 years or older, in men who are 70 years or older, in selected postmenopausal women and men with clinical risk factors for fracture, and in all adults who have experienced a fracture. All postmenopausal women (regardless of whether they are at risk for osteoporosis or not) should be encouraged to take steps to prevent bone loss and fractures, such as eating a balanced diet, obtaining adequate amounts of calcium and vitamin D, participating in appropriate exercise, avoiding excessive alcohol consumption and tobacco use, and taking measures to prevent falls. Bisphosphonates (such as Alendronate and Risedronate) are the first-line agents for both treating and preventing osteoporosis. Calcium (1,000 to 1,500 mg per day) and vitamin D (400 to 800 IU per day) are usually administered along with bisphosphonates. Other medications which may be of use include Raloxifene (which has estrogenic effects in certain tissues and anti-estrogenic effects in others), Calcitonin, and Parathyroid hormone. Once therapy is commenced, the BMD should be estimated via DXA after around 2 years, with an increase suggesting efficacy of treatment; DXA assessments should typically be performed every 2 years afterward. Note that more frequent testing may be warranted in certain clinical situations.


Take home messages

  1. Osteoporosis is usually clinically silent until a fracture occurs.
  2. Prevention of osteoporosis involves proper nutrition, exercise, lifestyle, and early screening.
  3. In women aged 65 and older and men aged 70 and older, screening via bone mineral density (BMD) estimation should be considered.
  4. Patient education plays a major role in reducing the burden of the disease.

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