A diagnosis of lumbar degenerative disc disease (lumbar DDD) as the cause of the patient's pain is a 3-step process:
- Patients' history, including when the pain started, a description of the pain and other symptoms, and activities, positions and treatments that make the pain better or worse.
- Physical exam, in which the physician examines the patient for physical signs of a symptomatic degenerated disc. This exam may include testing the patient’s range of motion, muscle strength, local tenderness, and more, with a focus on the lower back and legs.
- An MRI scan, which is used if lumbar DDD is suspected, as well as to rule out other potential causes of the patient’s symptoms.
MRI Scans and Degenerative Disc Disease
The magnetic resonance imaging (MRI scan) is used to confirm a formal diagnosis of lumbar degenerative disc disease and, if relevant, to aid in surgical planning.
MRI findings that are closely linked to a painful disc include:
- Disc space collapse of greater than 50%
- Cartilaginous endplate erosion.
Cartilaginous endplate erosion explanation:
- The disc space does not have a blood supply, but still has live cells within the disc space. These cells get their nutrition not from a blood supply but from diffusion through the endplate. Compromise to the endplate through the degenerative process leads to compromise of the cells nutrition. This can be best assessed on the T2 weighted scans done in the sagittal plane (looking at a cutaway of the spine in the upright position).
Normally, the endplate shows up as a black line (it doesn't have any water, and the T2 scan shows water content of tissues). If this black line is gone, the endplate is compromised.
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MRI findings that are more controversial, and are not consistently evidence of the cause of low back pain, include:
- MRI findings of early disc space degeneration, such as disc desiccation (meaning that discs are blacker on a scan because they do not have as much water as a healthy disc)
- A disc bulge, which shows the disc bulging out in one spot on an MRI scan
- An annular tear, which is a tear into the outer annulus of the disc space that shows up as a bright white spot on an MRI scan.
These subtle findings are for the most part just as likely to show up on a scan of someone who has not had pain as one who has had chronic low back pain. Also, these subtler findings are more consistent with natural aging of the lower back than of a pathological pain-producing disc space.
Disc degeneration is actually quite common among people who have no pain or other symptoms, so the patient’s history and physical examination are an essential part of the diagnosis.