Sciatica is pain down the leg caused by a lumbar (low back) disc compressing the exiting nerve (and these 5 lumbar nerve roots join together and form the large Sciatic nerve, hence the term Sciatica).
Sciaitca can involve tingling, pins and needles, burning pain, aching and weakness as these are all potential symptoms that can arise when the nerve is compressed (by a lumbar disc bulge), or chemically irrirated (called chemical radiculopathy–> Radiculopathy is a technical term for nerve symptoms travelling down the leg or arm).
Sometimes rather than a disc bulging on the nerve, physically compressing it, an annular tear (tear in the cartilage part of the disc) can leak inflammatory exudate (chemicals like those present when your ankle swells up after rolling it) giving rise to this chemical radiculopathy, or sciatica.
The diagnosis is usually formed by the clinical picture of leg symptoms as described above, plus or minus low back pain (it can occur without low back pain, and hiding the clue the back is the source of the leg pain for some patients).
MRI investigation can show a herniated disc with compression of the nerve root, but this is certainly possible and sometimes can be present without being seen on the scan (the MRI is done in lying typically and so the disc may not appear to be bulging as much in this view).
A good website with all the detail about this
is www.chirogeek.com and click on the Sciatica/Radiculopathy tab.
Clinically as a McKenzie Therapist we recongize symptoms of sciatica in your history, and then go about finding the Specifc movement that will reduce the disc bulging, which causes the symptoms to centralise (www.mckenziemdt.org and follow link to research at http://www.mckenziemdt.org/libResearchList.cfm?pSection=int#Cat1).
For some patients that dont respond (10-20%) the cause can be the chemical radiculopathy described above (as opposed to mechanical disc bulging causing compression), and treatment needs to include specific medications like NSAIDS (anti-inflammatory) or others like Lyrica (a neuropathic drug) to resolve this component of the symptoms.