Diagnostic Tests For Lower Back Pain

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[edit] Diagnostic Tests For Lower Back Pain

It can be quite challenging to the physician to diagnose the exact cause of lower back pain. As mentioned above, pain and a decreased range of motion are the obvious initial findings. The physician will check the patellar reflex and the ankle jerk reflex as a weak tendon reflex at the knee would point to a L3 or L4 nerve root compression.

On the other hand a missing ankle tendon reflex would be pointing to a S1 nerve root compression and would be associated with a drop foot. Should such signs be present (maybe only in 3 to 5 % of all acute lower back pain cases), a CT scan or MRI scan should be done to rule out a disc herniation. Often there might be an acute change in the first few days and then the irradiating pain into the leg would retreat and stay above the knee level.

This usually is a good sign and often no further testing is required, just reactivation. Often no testing other than observation by the physician has to be done up to 6 weeks into the acute back pain. As 90% of patients with acute lower back pain will have recovered within this period of time, much unnecessary testing and X-rays can be avoided. However, if symptoms persist, the phsyician has a number of options.

If osteoporosis and a compression fracture is suspected, plain X-rays can be ordered, which usually show the compression fracture. Degenerative changes in the spine show well on plain X-rays as well. However, the X-rays cannot distinguish between old or new compression fractures. A bone scan will show active uptake in a compression fracture that this is new. An old compression fracture would not show uptake on the bone scan.

The bone scan is also good as a screening method for bone metastases, but also for arthritis of facet joints, which is depicted well (e.g.spondyloarthropathies and degenerative arthritis). In sciatic pain, as mentioned above a CT or MRI scan should be ordered. These tests show the details of the relationship between the nerve roots, the bony structures and the discs. This way disc herniations, infections of discs (discitis) and nerve root compressions can be visualized. Degenerative changes of the discs show up really well on the MRI scan as dessication (loss of normal water content).

If a spinal stenosis is seen on an MRI scan, but the physician is not entirely sure about the extent of this or the effect on the nerve roots in terms of compression at possibly several levels, a myelogram can be done. Here the radiologist injects contrast dye, a radio-opaque material, into the subarachnoic space (inside the sac where the nerve roots go through) and more details can be seen, particularly, if this is combined with a CT scan. This test is called "post myelogram CT scan". A neurosurgeon likely will want to have these tests done before a surgical procedure would ever be contemplated, so the surgeon knows exactly what to expect before the surgery is being done. Appropriate blood tests would possibly be done as well depending on what condition the physician is looking for. This would include HLA B-27 to rule ankylosing spondylitis, RA titers to rule out rheumatiod arthritis or ANA titers to rule out lupus.

Here is a table that summarizes the more common causes for lower back pain.

Common causes of lower back pain
Cause or disease:	Comments:
facet joint disease (lower back strain)	may cause 80% of back pain
degenerative disc and facet joint disease	common in older patients
spondyloarthropathies	ankylosing spondylitis, psoriasis, ulcerative colitis, Crohns disease
osteoporosis	associated with compression fractures
scoliosis	congenital S-shape curve of spine
spinal stenosis	congenitally narrow spinal canal or acquired from degenerative changes
posttraumatic fibromyalgia	often following MVA's
disc herniation with or without sciatica	3% or less, needs surgery
spondylolisthesis and other congenital malformations	1 to 3 % of lower back pains
bone metastases	commonly from prostate, breast, colorectal, uterine, cervical or ovarian cancer
rheumatic illnesses	rheumatoid arthritis, lupus, ankylosing spondylitis

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