By Jeffrey Lotz
Jeffrey Lotz reviews what is required from new imaging techniques to improve the management of chronic low back pain. He will be speaking about this topic at the annual meeting of the International Society for the Advancement of Spine Surgery (ISASS; 3-5 April, Vancouver, Canada).
If you cannot measure it, you cannot improve it. Lord Kelvin.
A growing number of advanced imaging techniques are being developed to improve management of patients with chronic low back pain. Ideally, biomarkers from imaging provide valuable information about several aspects of disc disease, including diagnosis, severity, prognosis, and response to treatment. A fundamental challenge, however, is the lack of clear definition regarding what constitutes a diseased disc, and by extension, what relevant disease characteristics should be quantified with imaging. Historically, anatomic criteria such as disc height loss, nuclear/annular distinction, osteophytosis, herniation, and annular fissuring were developed to characterise degeneration progression.
Using these criteria, we now know that disc degeneration is age-related, physiologic, and mostly asymptomatic. Hence, anatomic findings unfortunately have limited diagnostic value for chronic low back pain because of their unclear relationship to symptoms. It may also be that lack of consistent improvement in outcomes is due to patient heterogeneity that is not captured by current anatomic criteria, leading to a mismatch between patient subgroups and intervention type. What is more, new high-resolution anatomic imaging techniques increase the identification of “incidental findings” that can trigger a cascade effect leading to further diagnostic procedures and treatments that can be costly and may pose additional risks to the patient. Consequently, current consensus recommends against the routine use of advanced imaging except in cases of suspected serious pathology and when progress is not being made with conservative care.
There is a pressing need for better understanding about why some discs hurt, and how non-invasive imaging can provide clinically actionable information related to diagnostics, treatment effectiveness, and patient-specific risk factors (approximately 70% of back pain/degeneration risk is related to individual factors). Basic studies are changing our understanding of back pain pathomechanisms and focusing our attention on functional characteristics and cellular behaviours, with the goal to repair and regenerate discs rather than remove them surgically. These innovative therapies require sensitive and specific imaging techniques that localise pain generators early in the disease progression and quantify treatment effects on disc chemistry and cell function. In this regard, “functional” imaging can provide useful information about chemicals, metabolites, or spinal biomechanics, the changes of which may represent biomarkers of pathological, painful disc features. These include MRI-based techniques such as T1-rho, T2-mapping, magnetisation transfer, sodium imaging, and MRI spectroscopy, or X-ray based techniques such as dynamic fluoroscopy and radio-nucleotide imaging. However, while changes in disc chemistry that occur with degeneration may have important clinical meaning, indications for use are not currently agreed upon.
For that reason, new imaging techniques need to be developed in close collaboration with clinicians who can help interpret the increasingly subtle findings these tests reveal, and clarify how these data can be valuable in the context of unmet needs of patients with chronic low back pain. With that solid clinical perspective, these diagnostic tests can be efficiently evaluated in clinical trials through comparison against established gold standards in an appropriate spectrum of subjects.
Jeffrey C Lotz, professor, vice chair of research, UCSF Orthopaedic Bioengineering Laboratory, San Francisco, USA