Intervertebral Disc Pain
Discs can begin to give trouble at almost any age but the most common age at onset is in the forties. It is estimated that 40% of younger adults with dominant backache have disc related pain. Therefore to comprehensively manage all cases of back pain, I believe it is obligatory to have accurate disc diagnostic tests and treatments available.
History. The history of disc pain is often similar. Usually there is a starting event which may be a bend, twist or lift or in women, all to often, childbirth. The pain cane disablingly severe and people often describe being incapacitad -stuck on he floor, bed, etc. Typically, there will be muscle spasm and listing to one side. This is usually described as “I put my back out”. The initial episode settles but recurs at an interval. Episodes become more severe, frequent, long-lasting until they are continuous, with exacerbations.
Pain Type and distribution. Disc pain is typically felt most towards the middle of the spin and relates to the level which is damaged. However it also spreads up an down the spin and often radiates to the legs/hips/groins usually in a pattern which is expected or predictable from the damaged level, but sometimes in very unexpected patterns. This is because each disc is served by a network of nerves and so has its nerve supply from multiple overlapping disc segments, as shown below.
The quality of the pain varies from purely somatic to neuropathic or mixed patterns. Occasionally it is associated with sympathetic activation. So it may be a deep ache or may have a nervy, tingly quality. Also, the disc when inflamed or bulging causes irritation of the nearby nerves so combinations of true nerve root and disc pain are usual. Characteristically, disc pain is most provoked by sitting and with forward bend, cough or sneeze and is characterised by episodes of muscle spasm, often causing the patient to lean or list to one side (compensatory scoliosis).
WHY? Disc pain is thought to start from tearing of the internal fibres of the disc annulus (internal Disc Derangement) as a result of the torsion forces and pressures they are subject to when we bend lift and twist (especially all together). As to why this happens: it just does. The discs are simply not always) strong enough for the job they have to do and there are inherited and other factors).
How? In health the deep parts of the annulus and the nucleus have no nerve supply and are not sensitive to pain. However, once internal tears start they can extend through the full thickness of the annulus distributing high pressures from the central nucleus, as below.
These tears stimulate an attempt at repair by an inflammatory response which progresses from the outside of the annulus into the deep layers (and eventually into nucleus in certain cases) which is thought to be responsible for much of the pain generation. One picture is worth a thousand words. The image below was taken by me of the side of a disc as I approached it for decompression by Disc FX. The red inflamed angry annulus is clearly visible, It should be white/yellow in health.
Sensory pain nerves grow into the deep layers of the annulus and transmit pain sensation, blood vessels invade and allow entry of inflammatory materials (and in specific cases bacteria: see Modic change). In the worst cases an inflamed mass of “granulation tissue” can form in the annulus (see below). Finally as well as pain from the disc itself, bulges and protrusions irritate the nearby nerves and most cases will finally have a complex mix of true disc and nerve generated pain. The cartoon below illustrates all of these features.
The Role of MRI scanning: MRI scanning is always necessary but not may not be sufficient on it’s own to make or exclude a diagnosis of disc pain. Importantly you cannot see internal disruption to the disc on MRI scanning, the disc may just look black (dehydrated) or slightly bulging but otherwise indistinguishable from age related change which is common. This is a key concept: you cannot take pictures of pain and more importantly you cannot take pictures of Not pain – the MRi usually just doesn’t resolve the diagnosis of what is hurting. However, it gives a road map of the possible pain generators which can be read intelligently in the context of the history and the examination. In order to know for sure if any individual disc is painful or not, you have to test the disc by provoking the pain (or not) by disc stimulation (pain provocation discography).
That said, certain features (a High Intensity Zone or HIZ in the annulus: see below) do correlate well with the finding of pain on further testing and can be a useful clue. Other which are highly predictive are severe advanced degeneration and Modic Change. A disc which is simply black or bulging is 50/50 in a case of typical disc pain. About 3-7% or MRI normal discs can respond to disc stimulation, which raises quite complex issues.
Diagnosis of Disc Pain: Pain Provocation Discography
Examination: A recent paper shows that the simple finding of pain provoked by deep palpation (compression) of the spin of the vertebra overlying the painful disc correlated strongly with the finding of pain at disc provocation (see below) so this is a simple screen.
Pain Provocation Discography: The definitive diagnosis is by Pain Provocation Discography. This is a debated technique. However, using the strict technical protocol developed by the ISIS group, I believe it is a valid test and proves useful and reliable in my practice. The principle is that a healthy disc can sustain injection of 2-3mls of x-ray contrast and up to 50PSI of injection pressure (but never more than 100PSI) without pain, while a disc which is painful at the time of testing will react strongly – in short the patient says “ouch”. If a standardised injection reproduces the patients typical pain of significant degree, while an adjacent disc is negative, the source of the pain is accurately localised.
This procedure is done under sedation, with x-ray guidance and with antibiotic cover to reduce the possibility of the rare (1:4000 approx) incidence of disc infection or discitis which can occur with any instrumentation of the disc. The patient is sedated comfortably, the needles positioned and then the patient wakened up. ONce alert the injections are given using a pressure monitoring injection system (CDS: Neurotherm)
The possibility that needling a healthy disc can cause damage to it has been raised by recent studies. This has also to be considered but is a contentious issue.