MRI follow-up of subchondral signal abnormalities in a selected group of chronic low back pain patients

Autor: Liisa Kerttula, Katariina Luoma, Mats Grönblad, Eeva Kääpä, Tapio Vehmas
Jazyk: angličtina
Rok vydání: 2008
Předmět:
Popis: Studies on detailed radiological evaluations of the spine remain essential to further our understanding of the pathoaetiologic factors behind the pain generator in ‘degenerative disc disease’ or DDD. DDD causing pain is a complex interplay of mechanical, traumatic, nutritional and genetic factors causing disc disruption and associated cell-mediated inflammatory responses. The presence of degenerative change on MRI, per se, is by no means an indicator of pain but subchondral abnormalities, termed ‘Modic changes’, have now been recently demonstrated to be inexorably linked to chronic low back pain [1, 3, 8]. Additionally, discographic evaluation has also shown to confer a significant association with painful internal disc disruption [5, 6, 9]. This is a prospective subgroup case series analysis (level IV study) looking at the radiographic evolution of acute subchondral signal abnormalities or Modic 1 (M1) endplate changes in patients with chronic low back pain. The study highlights the fact that acute M1 changes have a highly variable evolutionary course, which is very interesting from the radiographic perspective but its clinical relevance is somewhat uncertain. It remains tricky therefore for the readership to fully utilize the radiographic outcomes of this study in their day-to-day clinical practice. I would regard that the entire premise and importance of such a study hinges upon the clinical relevance of these M1 changes in patients with chronic low back pain and whether the evolution of M1 bears any clinical relationship on their associated low back pain. I suspect that many clinicians have now realised their importance, if not somewhat obsessed, and indeed become very are interested in its pathoaetiology, role as pain generator, and whether its presence is a predictor for good outcome following surgery, i.e. all areas pertaining to its clinical relevance in low back pain. Modic and Ross indicated that ‘the role of imaging is to provide accurate morphologic information and to influence therapeutic decision making’ [7]. Furthermore ‘a necessary component, which connects these two purposes, is accurate natural history data’. This study has certainly provided us with accurate morphologic data but lacks the natural history data and certainly provides no clues on how this will influence our decision making process, i.e. spinal fusion or disc replacement. Therefore, I anxiously await a clinically relevant follow-up study that the authors have resolutely indicated. Additionally, one must discern between ‘degenerative disc disease (DDD)’, which is deemed ‘pathologic’, i.e. causes severe low back pain, in young patients versus age related disc degeneration in the older populations. In that regard, the age for exclusion should therefore be set at less than 40 years. I understand from the authors that the prevalence of even relatively large M1 lesions in the base population of consecutive patients was low and it took 5 years to find the 24 cases with their inclusion criteria. Hence, it was decided also to include the 40–60 years old patients, who will clearly contain a mixed picture of ‘pathologic degenerative changes’ in addition to age dependent ones. This is complicated by the fact that Modic changes have been shown to be correlated with increasing age [2]. Another censure relates to the differential follow-up period. Given the well-known highly variable course of subchondral endplate inflammatory changes, the rationale for imaging patients at differing intervals will almost certainly have an important bearing on the temporal evolution of M1 lesions; the evolution of M1 over time in relation to clinical symptoms being fundamental to the raison d’aitre for conducting such an investigation. Therefore the detailed study on the evolution of subchondral abnormalities mandates similar temporal follow-ups between patients. The issue with Schmorl’s nodes also deserves mention. Granted Schmorl’s nodes are endplate abnormalities but they are, in effect, entirely separate subchondral pathologic entities from Modic endplate changes, both in regard to the pathoaetiology, natural history evolution, relevance to back pain, and anatomical endplate distribution. They typically occur in the adolescent spine and have little clinical bearing to adults with low back pain. Their distribution is typically central unlike anterior/eccentric as in Modic changes; the latter is probably due to abnormal biomechanical endplate loading akin to MRI changes seen in end-stage hip or knee osteoarthritis. Therefore, one should be a little guarded by the fact that significant emphasis has been placed on these Schmorl’s nodes, which is likely a pre-existing radiologic entity. Finally MRI of the spine has become an important aspect in the evaluation of patients with low back pain. I would critically question the use of dissimilar MRI equipments; that is dissimilar in manufacture and magnet strengths, because this would invariably invalidate the quality and hence assessment of MRI images. Additionally, it is common knowledge that increasing MRI Tesla rating not only improves the speed of obtaining imaging but more importantly, the resolution and hence the subtleties of interpreting subchondral endplate abnormalities [4]. I would critically state that ‘using T1- and T2-weighted TSE and FSE sequences’ does not constitute a properly defined protocol. The correct selection of the TE time of the MRI pulse sequence helps to control the amount of T1 or T2 contrast present in the image and hence will have a major bearing on the degree of (acute) oedema seen within the endplates, aka M1, in patients that typically have acute low back pain. In short the interpretation of this study needs to be somewhat guarded. There are a number of areas that need to be re-evaluated, in particular, appropriate MRI imaging protocols, the utilization of comparable MRI-manufactured equipments, similar temporal follow ups, the inter-relationship between these radiographic modulations and low back pain (i.e. natural history data), and above all, how clinicians may be able to influence these changes with therapy, be it pharmacologic or surgical manipulations.
Databáze: OpenAIRE
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