The diagnosis of back pain is subjective and identifiable only by the patient. There is no real way to prove or disapprove someone’s pain. Attempts to refine or specify the diagnosis have had little impact on the success of treatment. One explanation for this is that we tend to lump back pain into one category, while it may actually be many different subcategories. If we can easily distinguish and identify these subcategories of back pain, we would be able to treat more specifically and yield more success.
Discogenic vs. Facetogenic Pain
When back pain persists and it is mechanical (pain with movement), it may be helpful to separate the cause of the pain into discogenic and facetogenic. Discogenic pain tends to worsen with sitting and improve with standing or lying down. Facetogenic pain is the opposite. It improves with sitting and worsens with standing or lying down.
If the pattern of a patient’s pain is consistent with a discogenic or facetogenic origin, it may be helpful for the patient to undergo an imaging diagnostic tool, such as magnetic resonance imaging (MRI).
The MRI is the best test to use when looking for the cause of back pain. It is the most sensitive and can occasionally identify inflammation of the facet joints or a disc herniation. If the pain is not mechanical and pain is occurring whether or not the patient is in motion, taking an MRI of the abdominal or pelvic cavities may reveal a non-spinal origin of the back pain.
Further testing is done by use of diagnostic injection. If facetogenic pain is suspected and an MRI shows a probable inflamed facet joint, the diagnosis can be made more definitive by doing a median branch block of the facet joint. By anesthetizing the nerve to the capsule of the joint, reduction of pain is more evidence that the pain is arising from the facet joint.
Similarly, for patients with discogenic pain, an injection can be used to identify a disc as a pain generator. In this setting, fluid is injected into the disc space to see if it will duplicate the pain. Following the injection, an anesthetic can be injected for pain relief.
Occasionally, bone scans are used to look for increased metabolic activity in either the facet joint or disc space. This may serve as a marker for inflammation and help identify a pain generator. This test can also identify a stress fracture of a vertebral body, which could also be the cause of the pain.
If there is associated leg pain, the pain in the leg may indicate a problem with a nerve root of a specific lumbar (lower back) vertebrae. A bone scan can be helpful in localizing the segment of the spine that is generating the pain.