Infographics

MRI for Back Pain

By: Sridhar Nadamuni

Globally, back pain ranges from a single-day prevalence of 12% to a month-long agony in 23% of all cases, with females in the age group of 40 to 80 years showing the highest rates.[1] The total costs associated with low-back pain in the United States exceed $100 billion annually.[2] Smoking, obesity, and advancing age are the top three risk factors. Female gender, physical or psychological stress, sedentary occupations, poor education, living on unemployment insurance, professional dissatisfaction, and psychosomatic disorders increase the risk for back pain.[3],[4],[5]

Etiology of Back Pain

Non-specific back pain occurs in more than 85% of all cases.[6] Most cases are probably musculoskeletal in nature, and usually resolve within a few weeks.

Systemic causes such as compression of spinal cord or cauda equina syndrome, metastatic cancer and spinal cord infection are associated with 1% of all cases.[7] Cord compression is most commonly triggered by intervertebral disc herniation, although ankylosing spondylitis, lumbar puncture, trauma, benign and malignant tumors, and infection are the other causes. Pain is the initial symptom. A history of cancer greatly increases the risk of back pain due to metastatic (mostly from breast, prostate, and other cancers) bone disease.[8]  Epidural abscess of the spinal cord may occasionally trigger radicular pain and neurologic deficits.Vertebral osteomyelitis following bacteremia mostly affects males and may trigger back pain.

Less common etiologies include osteoporotic fractures of vertebrae, radiculopathy, lumbar spinal stenosis, osteoarthritis, scoliosis and hyperkyphosis. Symptoms of low back pain may also be triggered by piriformis syndrome, sacroiliac joint abnormalities, and Bertolotti’s syndrome.9

Indications for MRI

MRI is promptly indicated for patients manifesting signs of urinary or fecal incontinence or inability to urinate or pass stools, gait disorders, worsening numbness in a single leg, recent falls or injuries, fever, history of cancer, and severe back pain that is refractory to medications.9 Guidelines recommend MRI or CT “in patients who have severe or progressive neurologic deficits or are suspected of having a serious underlying condition (such as vertebral infection, the cauda equina syndrome, or cancer with impending spinal cord compression) because delayed diagnosis and treatment are associated with poorer outcomes”.[10] MRI is preferred over CT because it offers better insight into soft tissue disorders, vertebral column and spinal cord conditions.[11]

Patients with neurologic deficits such as those suffering from spinal cord compression should promptly undergo MRI for further assessment. Symptoms to watch include urinary retention, loss of urinary and fecal control, and motor disorders that cannot be traced to a single nerve root.9

A high degree of clinical suspicion for spinal infection attributed to vertebral osteomyelitis or even epidural abscess warrants MRI. MRI shows the maximum sensitivity (0.96) and specificity (0.92) as an imaging modality for screening patients with spinal infection.[12]The causes for clinical suspicion may include a recent history of spinal intervention or ongoing intravenous medications, along with high fever and focused back pain. In fact, the sensitivity of X-rays for spinal infection diagnosis is lower (0.82) and plain radiography is less specific (0.57) compared with MRI.12

MRI is also the choice in patients with metastatic bone disease and is indicated when plain radiography fails but the patient reveals high levels of ESR and CRP.9 Bone metastases trigger back pain. It is imperative that those at high risk based on age, smoking status, family history, and/or physical examination are assessed with MRI, rather than plain radiography that has a sensitivity and specificity of 0.60 and 0.95, respectively, for malignancy.12

However, the most common indications for MRI are patients with symptoms suggestive of “pinched nerve” or radiculopathy, especially the lumbosacral type, or lumbar spinal stenosis refractory to conservative approaches need to undergo MRI before contemplating surgery or epidural interventions.[13]

Diagnostic Implications

According to the American College of Physicians, “diagnostic imaging is indicated for patients with low back pain only if they have severe progressive neurologic deficits or signs or symptoms that suggest a serious or specific underlying condition.”13

Most patients with symptoms of back pain seen by the primary care physician relate to nonspecific back pain, which generally subsides over a few weeks following conservative measures. However, in less than 1 percent of all cases, serious systemic illnesses such as cancer or infection may trigger back pain. In fact, less than 10 percent of all patients with back pain have specific disorders associated with the musculoskeletal disease, such as vertebral compression fracture, “pinched nerve”or radiculopathy, and spinal stenosis.9

A regular history and physical examination may be adequate in most cases of nonspecific back pain that disappears with a month. However, less than 1 percent of all cases evaluated by the primary care physician warrant immediate advanced imaging for further diagnosis and appropriate treatment.9

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Recent Advances in MRI-based Diagnosis and Treatment of Back Pain

Recent advances suggest that axial-loaded MRI is preferable to recumbent MRI in obese patients suffering from back pain. It may enhance the diagnostic benefit of lumbar spine MRI in such individuals with possible spinal canal stenosis.[14]

Screening with a rapid lumbar spine (LS) MRI protocol using a single 3D-T2  fat-saturation sequence in patients with acute back pain admitted to the emergency department revealed fractures, cord signal abnormalities, and severe spinal canal stenosis in addition to detecting cord compression more rapidly and effectively than conventional LS MRI.[15]

The coronal short tau inversion recovery (STIR)-weighted magnetic resonance (MR) sequence, incorporated in lumbar spine MRI allowed the detection of extraspinal degenerative conditions contributing to lower back pain: sacroiliac joint defects, sacroiliitis, degeneration of the coxofemoral joint, renal and adrenal masses, genitourinary infarcts, hydronephrosis, renal stones, aortic aneurysm, retroverted uterus and pelvis, ovarian cysts, inflammatory pelvic disease, and bone metastases excluding vertebral involvement.[16]

A management strategy involving routine intervention with an up-front MRI may reduce the treatment duration and consultation with clinicians, without increasing the referral rates for back surgery or the costs involved.[17]

Conclusion

Further studies analyzing the cost-effectiveness and benefits associated with different MRI approaches in managing low back pain are needed. Also, MRI findings should be evaluated in conjunction with clinical observations for a definitive diagnosis of back pain.

 

REFERENCES

[1]A systematic review of the global prevalence of low back pain. Arthritis and Rheumatism.doi: 10.1002/art.34347. Accessed August 22, 2018.

[2]Lumbar disc disorders and low-back pain: socioeconomic factors and consequences. The Journal of Bone and Joint Surgery. https://www.ncbi.nlm.nih.gov/pubmed?term=16595438. Accessed August 22, 2018.

[3]The Saskatchewan health and back pain survey. The prevalence of low back pain and related disability in Saskatchewan adults. Spine (Phila Pa 1976). 1998 Sep 1;23(17):1860-6; discussion 1867.https://www.ncbi.nlm.nih.gov/pubmed?term=9762743. Accessed August 22, 2018.

[4]What triggers an episode of acute low back pain? A case-crossover study. Arthritis Care & Research.doi: 10.1002/acr.22533.Accessed August 22, 2018.

[5]Psychologic distress and low back pain. Evidence from a prospective study in the general population. Spine.https://www.ncbi.nlm.nih.gov/pubmed?term=8747252. Accessed August 22, 2018.

[6]Diagnosis and treatment of low back pain: a joint clinical practice guideline from the American College of Physicians and the American Pain Society. Annals of Internal Medicine. http://annals.org/aim/fullarticle/736814/diagnosis-treatment-low-back-pain-joint-clinical-practice-guideline-from. Accessed August 22, 2018.

[7]What can the history and physical examination tell us about low back pain? JAMA. https://jamanetwork.com/journals/jama/article-abstract/399079. Accessed August 22, 2018.

[8]Cancer as a cause of back pain: frequency, clinical presentation, and diagnostic strategies. Journal of General Internal Medicine. https://www.ncbi.nlm.nih.gov/pubmed?term=2967893. Accessed August 22, 2018.

[9] Evaluation of low back pain in adults. UpToDate. https://www.uptodate.com/contents/evaluation-of-low-back-pain-in-adults. Accessed August 23, 2018.

[10]Diagnosis and treatment of low back pain: a joint clinical practice guideline from the American College of Physicians and the American Pain Society. Annals of Internal Medicine. http://annals.org/aim/fullarticle/736814/diagnosis-treatment-low-back-pain-joint-clinical-practice-guideline-from.Accessed August 23, 2018.

[11]Diagnostic evaluation of low back pain with emphasis on imaging. Annals of Internal Medicine.http://annals.org/aim/article-abstract/715687/diagnostic-evaluation-low-back-pain-emphasis-imaging?volume=137&issue=7&page=586. Accessed August 23, 2018.

[12]Diagnostic evaluation of low back pain with emphasis on imaging. Annals of Internal Medicine.http://annals.org/aim/article-abstract/715687/diagnostic-evaluation-low-back-pain-emphasis-imaging?volume=137&issue=7&page=586. Accessed August 23, 2018.

[13]Diagnostic imaging for low back pain: advice for high-value health care from the American College of Physicians. Annals of Internal Medicine. http://annals.org/aim/fullarticle/746774/diagnostic-imaging-low-back-pain-advice-high-value-health-care. Accessed August 23, 2018.

[14]Diagnostic Benefits of Axial-Loaded Magnetic Resonance Imaging Over Recumbent Magnetic Resonance Imaging in Obese Lower Back Pain Patients. Spine (Phila Pa 1976). doi: 10.1097/BRS.0000000000002532.Accessed August 21, 2018.

[15]Less Is More: Efficacy of Rapid 3D-T2 SPACE in ED Patients with Acute Atypical Low Back Pain. Academic Radiology.  doi: 10.1016/j.acra.2017.02.011. Accessed August 23, 2018.

[16]Clinical impact of coronal-STIR sequence in a routine lumbar spine MR imaging protocol to investigate low back pain. Medicine. doi:  10.1097/MD.0000000000010789. Accessed August 23, 2018.

[17]Routine versus needs-based MRI in patients with prolonged low back pain: a comparison of duration of treatment, number of clinical contacts and referrals to surgery.Chiropractic& Osteopathy. doi:  10.1186/1746-1340-18-19. Accessed August 23, 2018.