The Study | Results | Discussion | Doug's Discussion
Schwarzer AC, Aprill CN, Derby R, Bogduk N, Kine G. “ The prevalence and clinical features of Internal Disc Disruption in patients with Chronic Low Back Pain. ” Spine 1995; 20(17):1878-1883
It is common knowledge amongst the medical and research community that not all patients with chronic back and leg pain suffer from compressive disc herniation and/or stenosis. In his 1986 presidential address, Dr. H. V. Crock told members of the international spine society that internal disruptions within the architecture of the disc could result in back pain and even lower limb pain without the presence of spinal nerve root compression (9). He termed this entity ‘Internal Disc Disruption’ or IDD.
To test and further develop Crock’s theory of IDD, a ‘Dream Team’ of well respected researchers designed a investigation which calculated the prevalence (frequency) of Internal Disc Disruption in patients with chronic low back pain. The study also attempted to determine if traditional examination findings and/or specific patient symptoms could be predictive of the diagnosis of IDD.
By following the strict criteria specified by the ‘International Society for the Study of Pain in its taxonomy’ (21), these investigators calculated the prevalence of IDD to be between 30% and 50% with a 95% confidence limit. They also concluded that neither traditional examination findings nor patient symptoms could predict whether or not a patient had IDD. Unfortunately, it looks like provocation discography remains the only way to confirm the diagnosis of IDD.
The Study:
Ninety-two chronic back and/or leg pain patients were gathered for an investigation into the prevalence of internal disc disruption (IDD). All of these 61 men and 31 women all had negative MRIs and/or CTs for compressive disc herniations or stenosis or anything else that could compress the nerve roots and cause pain in the lower extremities.Patients were excluded from this study for the following reasons: 1) being over 80 years of age; 2) being under 18 years of age; 3) having had previous spinal surgery; and 4) having signs of neurological compromise in the lower extremities upon examination, i.e., decreased reflexes, muscle atrophy and weakness, and/or loss of sensation in a dermatomal distribution.
All ninety-two patients were carefully examined and asked the exact location of their pains. Any radicular pain into the lower extremity was classified as to how far down it traveled. The categories were as follows: to the butt, to the knee, to the calf, or to the foot. (I was extremely disappointed to learn that the authors chose not to present this data in the paper.) The examination included a Range of Motion assessment, Kemp's Test (rotation w/ extension), and the Straight Leg Raising Test.
After the examinations and histories were complete, the investigation moved into the actual ‘diagnostic phase’; all patients were put through Provocative Discography and CT Discography in accordance with criteria adapted by the International Society for the Study of Pain in its taxonomy (21) and the North American Spine Society (10).
The patient was declared to have IDD only when the following criteria were met: ►) no visible disc herniations were observed on imaging; ►) injection of the suspect disc with contrast had to ‘recreate’ the patient's exact back and leg pain(i.e., concordant pain) (9); ► injection of at least one disc above or below the suspect disc had to be non-painful (i.e. a control disc); and ► a grade 3 or 4 radial anular fissure had to be demonstrated on CT discography (i.e., a full thickness annular tear) (2).
ONE SERIOUS CONFOUNDER: Unfortunately, 79% of the patients entered into this study were involved in litigation. More explicitly, 56% of them had pending Workers’ Compensation claims and 23% had pending third party claims. The literature is quite conclusive on the on the notion that workers compensation or personal injury patients don't do well in outcome scoring as they often have ulterior motives for not admitting to improvement.
RESULTS:
The bottom line of this study was this: using 95% confidence limits, the prevalence of IDD lies between 30% and 50%.
The L5 disc was most often found to be positive for IDD (20.5%); this was closely followed by the L4 disc (20%), then the L2 disc (19%), and finally the L3 disc (9.5%). IDD was not found in any L1 discs.
Only thirty-six (39%) of the 92 patients satisfied the criteria for IDD and were given the diagnosis, although this percentage might be a little higher in reality (see Doug’s Discussion).
There was “no statistically significant association between historical or examination findings and whether patients had a positive discogram (which yielded the diagnosis of IDD).” In English, there was no piece of patient history or examination finding that could predict that the patient was suffering from IDD, as determined by provocation discography.
The authors have demonstrated that by using a specific set of recognized criteria, the diagnosis of IDD could be made with high confidence in a group of chronic back and leg pain patients, and that the percentage (prevalence) of chronic back pain sufferers who have IDD is “not negligible” (significant).
To all the opponents (doubters) of IDD and discography (which go hand-in-hand) the investigators stated that now “there is no justification for denying, ex cathedra, the existence of IDD… for it has been shown that IDD is a common, but by no means universal entity in patients for whom no rubric (category) is available other than ‘low back pain of unknown origin’.”
They acknowledged that the proponents (supporters) of IDD would also be disappointed with these rather low prevalence rates (30% to 50%). They noted that one possible explanation was due to the “application of stringent criteria” in confirming the diagnosis of IDD. They speculated that by loosening the criteria, “particularly… the need for a negative (non-painful) control disc”, the prevalence of IDD would rise. However, the authors’ concur (agree) with the recommendations of the ‘International Society for the Study of Pain in its Taxonomy’ (21) and believe this stringency (strictness) is needed to avoid falsely diagnosed cases of IDD, which may expose patients to unwarranted – and probably unsuccessful – surgery.
Blunder: Who in their right mind would conduct an investigation, especially one that relied heavily on patient honesty, using a patient-study-base that was predominantly (79%) made of Workers’ Compensation and Third-Party-Accident patients! The fact that these patients had failed to recover from their accidents despite having 18 months of conservative care, normal imaging studies, and normal neurological examinations only lends support to my believe that some of these patients were probably 'malingering' (faking the amounts of their pain) to some degree in hopes of improving the monetary awards given for their permanent disability. If malingerers did get into the study, they would have most likely 'flunked' provocation discography, for this is one test that the patient can not manipulate. For example, in order for discography to be positive for IDD, the patient must not only have a pain producing disc, but also must have at least one disc that does not produce any pain at all (a control disc). The latter criteria is where the authors noted that if relaxed, the numbers of IDD cases confirmed by discography could have been dramatically improved. I would bet you that some of these malingerers reported pain on disc injection when they really didn't have any at all, hence lowering the prevalence of IDD and the validity of the results.
Having spent 17 years in the Bay Area - which is where half of the patients in this study came from - treating Workers' Compensation Patients and Third Party Patients, I can attest to the litigious disposition of many of these types of people.
Therefore, I believe the prevalence rate of IDD is much higher than the 40% that was calculated in this study; however, even at a prevalence rate of 40%, IDD is still considered to be the most common cause of chronic lower back pain. (1)
To date, this study is still the only investigation that has attempted to find the prevalence of Internal Disc Disruption in the Chronic Pain Population. It's to bad that a better, less litigious group of patients couldn't have been used, for if they had I would bet you the prevalence of IDD in the chronically disabled would be upwards of 80%.
The other thing I was upset by is the fact that this brilliant group of investigators failed to publish their data on the prevalence of lower limb radicular type pain (discogenic sciatica) from this group of patients. They only gave Kappa scores to show that lower limb pain was non-predictive of IDD. Lower extremity pain referral from the disc is a fascinating area of research and this study could have lent some data to the cause.
REFERENCES:
1) Bogduk N, McGuirk in: "Pain Research & Clinical Management. Medical Management of Acute & Chronic Low Back Pain: An Evidence-Based Approach" Amsterdam, The Netherlands 2002; Elsevier Vol13:122
10) Executive Committe of the North American Spine Society. Position statement on discography. Spine 1988; 13:1342
2) Aprill CN, Bogduk N. “High-intensity zone: a diagnosis sign of painful lumbar disc on magnetic resonance imaging.” Br J Radiol 1992; 65:361-9
9) Crock HV, Internal disc disruption. A challenge to disc prolapse fifty years on. Spine 1986 ;11:650-3
21) Merskey H, Bogduk N. “Classification of Chronic Pain: Descriptions of Chronic Pain Syndromes and Definitions of Pain Terms.” Seattle: IASP Press, 1994:180-1