Discogenic lower back pain is pain that originates from the discs of the lumbar spine and it is the most common cause of chronic lower back pain. Diagnosis of this type of pain uses a physical history, physical examination, imaging tests, and possibly discography
Editorial Note: While discography is a fairly common procedure to diagnose disc pain, but there is some controversy regarding the procedure's significance to an accurate diagnosis.
Discogenic lower back pain is pain that comes from the disc. Now, discogenic lower back pain is the most common cause of chronic lower back pain. It accounts for about forty percent of chronic lower back pain - chronic being defined as anything that lasts longer than three months.
When people think of pain coming from the disc in the spine, they typically tend to think about herniated discs. Herniated discs don't cause lower back pain. Herniated discs may approximate a nerve and that can send pain going down into the leg, but a herniated disc in and of itself isn't really what's causing the lower back pain. A tear inside of the disc is where back pain from the disc is actually coming from. Essentially the disc is like a jelly donut. There's this inner jelly that are full of all of these inflammatory proteins - Interleukin 1, TNF-Î±. It's called the nucleus pulposus and it gives the cushioning to the disc so that the bones aren't rubbing on each other. There are no nerve fibers in that inflammatory soup in the middle of the disc and, so it's okay that inflammatory proteins are there. In the outer third of the crust of the disc - in the outer third of the annulus fibrosis - there are nerve fibers. What happens when people have pain that comes from the disc is there's a tear inside of the disc and the jelly in the middle of the disc oozes out and irritates the outer third of the crust of the disc and that's where pain from a disc, when it’s lower back pain, actually comes from. Now, that can happen in conjunction with a herniated disc - and it can happen in the absence of a herniated disc; so sometimes on an MRI you don't see a herniation - that doesn't mean the pain isn't coming from the disc.
Discogenic lower back pain typically presents with pain with sitting, with bending forward. The disc feels the most mechanical stress in about thirty degrees of trunk flexion, so things like picking up kids, picking up laundry, brushing teeth - those tend to provoke more pain when the pain is actually originating from the disc. Since people do a lot of sitting during the day and sitting is about the second-worst mechanical position for the disc, often people will note that the pain is worse as they're sitting.
How is Discogenic Lower Back Pain Diagnosed?
The diagnosis of discogenic lower back pain begins, like other causes of lower back pain, with a good history and a good physical examination. Now, history and physical examination will often point the physician towards the diagnosis of discogenic lower back pain, but they're not going to be definitively diagnostic of discogenic lower back pain. Often the doctor will order an x-ray or an MRI. On an MRI, you may be able to see a tear in the annulus fibrosis. You see what is called an "area of high intensity" on the MRI. You’re not always going to see that, even when there's a tear; you'll see it about thirty percent of the time, if one actually exists, and frankly you can also have a tear in the disc and that doesn't necessarily be the cause of pain. So, you take all of your imaging with a grain of salt and you have to put it into the context of the entire person. It goes back to the important teaching point that we need to treat people and not just treat MRIs.
There is a more definitive diagnostic procedure to evaluate for discogenic lower back pain and that's something called a "provocative disc stimulation" or "discography." That's a procedure where you put a needle into the disc, under an x-ray, and you put some contrast into multiple discs to see whether or not, by introducing pressure into the disc, you reproduce the typical pain. When that typical pain is reproduced, then you will often get a CAT scan afterwards and look on the CAT scan to see whether or not there's a tear in the disc and you can see the contrast extravasate out through the tear into the annulus fibrosis, if one exists.
That's a relatively invasive procedure and we don't do it very often. We do it really only if we’re considering surgical options - so if all conservative options have failed and we're thinking about a fusion surgery, or some other kind of surgical procedure, or we just need to know more definitively what the cause of the chronic lower back pain is, then a provocative disc stimulation is always an option we can employ.
More typically, we rest our diagnosis of discogenic lower back pain on the history, on the physical, on the MRI and putting all of these features together and sometimes also ruling out other potential causes of chronic lower back pain.