SPECT/CT Imaging of Lumbar Joint Pain
Low back pain is an all too common problem, with chronic low back pain (of at least 3 months duration) often causing significant disability and imposing an enormous social and economic burden.
At any given time, 12-33% of the adult population has low back pain, of which the majority is termed non-specific, implying that there is no value in identifying the specific cause. Although the prognosis is uncertain, the majority improve within the first few weeks, with approximately half of the remainder resolving by 12 months 1.
Despite this reassuring fact, those suffering understandably desire a more rapid resolution of their symptoms. Attempting to identify the specific cause of pain would be useful only if a specific beneficial treatment option results. This scenario exists for pain arising from the lumbar spine facet joints.
Ghormley first coined the term facet joint syndrome in 1933 when discussing alternate sources of low back pain 2. Lumbar spine facet joint pain may affect many patients with chronic low back pain, with a wide estimate of between 5-90% 3. The causative relationship between facet joint arthropathy and low back pain has been questioned since the majority of people with advanced facet joint degeneration, as found on structural imaging, are asymptomatic 4. As a result, abnormal morphology may not necessarily reflect underlying pathology. In this instance, a functional imaging technique may be of greater value, such as with SPECT nuclear imaging.
As lumbar spine facet joints are synovial joints, they are demonstrated on bone scans. The addition of SPECT imaging improves the sensitivity and localisation of activity above that achieved with planar imaging alone 5,6.
Holder et al 7 found that SPECT imaging of the lumbar spine in 58 consecutive patients with possible facet joint syndrome proved to be 100% sensitive and 71% specific for the clinical diagnosis of facet disease. Dolan et al8 then showed that positive SPECT findings predicted good response to targeted injection therapy in 95% of participants. This finding was replicated more recently by Pneumaticos et al9 who also found 87% of patients who underwent facet joint corticosteroid injections, as directed by the SPECT findings, had a significant reduction in pain compared to those in whom the site of injection was determined by clinical assessment.
Despite these impressive findings, the relatively lower specificity needs improvement. The limitation of SPECT imaging is the lack of image sharpness or resolution, this being necessary to definitively identify which level/s the disease affects. This is particularly problematic given the small size of the facet joints and their proximity to each other and the surrounding bony structures (such as the pars interarticularis and vertebral bodies).
The recent development and use of image fusion has promised to address these concerns. The co-registration of functional and structural information within the same study provides a means of improving the accuracy of identifying the culprit facet joint/s. A small study using a computer algorithm to fuse the SPECT and CT data demonstrated an improved ability over SPECT alone in differentiating activity between L4/5 and L5/S1 facet joints (this is the common site of confusion with SPECT imaging alone) 10.
In conclusion, the majority of patients with non-specific low back pain can expect resolution of their symptoms, albeit in some, by 12 months. In this group there is value in identifying those in whom the cause is active facet joint arthropathy, since a directed corticosteroid injection to the culprit joint/s can hasten their symptomatic recovery. SPECT/CT imaging is likely to be proven as the ideal investigation in this group given the combination of functional and structural information obtained.
References
1.Menezes Costa et al. Prognosis for patients with chronic low back pain: inception cohort study. BMJ. 2009; 339: b3829.
2.Ghormley RK. Low back pain with special reference to the articular facets with presentation of an operative procedure. JAMA. 1933; 101: 10773-10777.
3.Cohen SP, Raja SN. Pathogenesis, diagnosis, and treatment of lumbar zygopophyseal (facet) joint pain. Anesthesiology. 2007; 106: 591-614.
4.Kim KA, Wang MY. MRI-based morphological predictors of SPECT positive facet arthropathy in patients with axial back pain. Neurosurgery. 2006; 58: 147-155.
5.Collier BD et al. Bone SPECT. Seminars in Nuclear Medicine. 1987; 17: 247-266.
6.Gates GF. SPECT imaging of the lumbosacral spine and pelvis. Clinical Nuclear Medicine. 1988; 13: 907-914.
7.Holder L et al. Planar and high-resolution SPECT bone imaging in the diagnosis of facet syndrome. Journal of Nuclear Medicine. 1993; 36: 37-44.
8.Dolan AL et al. The value of SPECT scans in identifying back pain likely to benefit from facet joint injection. British Journal of Rheumatology. 1996; 35: 1269-1273.
9.Pneumaticos SG et al. Prediction of short-term outcome of facet joint injection with bone scintigraphy. Radiology. 2006; 238: 693-698.
10.McDonald M et al. Use of computed tomography – single photon emission computed tomography fusion for diagnosing painful facet joint arthropathy. Neurosurgical Focus. 2007; 22: 1-4.
