Hi Mitsuyo,
to answer your queries:
1. Nerve root clumping does not always show up, especially if either the scan resolution was too poor, or more commonly, the radiologist wasn't looking for it, or sometimes in the early stages of AA it is difficult to image. Radiculopathy simply means abnormality of nerve root(s) and can arise from a number of different causes, usually a 'slipped disc' impinging on the root: which shows up as the prolapsed disc rather than demonstrating the actual damage to the nerve root. MRI shows anatomical abnormalities not physiological ones (nerve pain can come on with as little as about 10% compromise of function, which may not be visible on anatomic scans), and although it shows a lot, is often not specific. Ditto for CT scan. Also, if you have hardware (screws etc.) in your spine, this will cause 'artefacts' in the imaging, i.e. distortions which make interpreting the scans very difficult if not impossible. Hence the need for a CT myelogram. This should demonstrate significant filling defects in nerve root sleeves or the subarachnoid space (abnormal CSF flow) but again, it doesn't directly show nerve damage as such. We also have to bear in mind that MRI scans are done with the patient lying flat, which doesn't show what happens when you sit up or stand (or walk). The postural differences (which tend to be when symptoms occur) are therefore not taken into account.
2. EMG/NCS are physiological tests of nerve function. However, they concentrate primarily on motor (movement) function and pain is a sensory function. So they are less likely to be abnormal in AA unless there is some weakness as well as the pain/abnormal sensations. I don't recommend these tests as helpful in diagnosing AA.
I tend to make a diagnosis based on the history: i.e. have you had risk factors for AA (surgery, myelogram etc.) plus the symptom complex (although that can be quite non-specific and mimic other chronic pain syndromes such as fibromyalgia).
I hope this clarifies things for you.
Regards,
DocSarah
