In reply to Dr R Defrin et al

Abstract

Thank you for the opportunity to respond to the comments by Defrin and colleagues regarding our review and in particular the relationship between pain and physical factors following spinal cord injury (SCI). We agree wholeheartedly that it is dicult to determine a clear correlation between the presence or intensity of pain following SCI and speci®c physical or psychological factors. Indeed the often con ̄icting reports that we presented highlight the complexity of this issue and the diculty in assigning any one variable as a predictor or correlate of pain. We did report studies that concluded that psychosocial factors were more important than physical factors. However, this was done in the context of a review of other studies that have suggested that certain physical factors may also be associated with pain. Therefore we did not intend to communicate that psychosocial factors alone are the sole predictors of pain following SCI. What our review did intend to communicate, however, is that many of these studies are contradictory and therefore there is at present little de®nitive evidence for a correlation between the presence or severity of pain and any one physical variable associated with the injury. We acknowledge the ®ndings of Defrin et al of a relationship between completeness and increased severity of SCI pain. Most studies have examined a relationship between the presence rather than severity of pain, and a number have suggested an association between the presence of pain and incompleteness ± 6 although another has suggested a relationship with completeness. Other studies have failed to ®nd any relationship between either the presence ± 10 or severity of pain and completeness. These di€erences may be due to several factors such as the types of pain included (eg any pain or only neuropathic), the level of injury of those investigated (all levels or lumbosacral only) and the measures used to assess pain severity. However, in the presence of such con ̄icting information, it is dicult to assert that there is a strong association between the presence or severity of pain and either completeness or incompleteness. The second issue of concern raised by Defrin and colleagues is the relationship between pain and damage to speci®c spinal pathways. There appear to be two contentious issues: whether spinothalamic tract damage is a necessary prerequisite for the development of neuropathic SCI pain, and whether neuropathic SCI pain is more likely to occur with loss of spinothalamic inputs when there is relative preservation of dorsal column inputs. There appears to be virtually unanimous support for the importance of spinothalamic tract damage in the development of neuropathic pain. ± 18 Studies that have documented sensory de®cits consistently indicate that all patients with pain have de®cits of temperature and pin prick sensation. These studies all support the proposal that spinothalamic tract damage is a necessary prerequisite of neuropathic pain. The only study that disagrees with this assertion is the study by Eide et al who found no signi®cant di€erence in the mean threshold values for thermal stimuli between painful and non-painful areas. It is not apparent from their study whether any subjects were found with normal thermal sensation and pain and therefore whether the hypothesis can be refuted. We agree that the bulk of evidence supports the proposal that spinothalamic tract damage is a necessary ingredient in the development of neuropathic SCI pain. However, there is a necessary quali®cation to this statement. Although this may be the case for below-level neuropathic pain, it may not be the case for all cases of neuropathic pain. Nathan reports cases of patients with hyperaesthesia and hyperpathia following lesions that appear to be con®ned to the dorsal columns and allodynia is common following central cord injuries that do not appear to involve spinothalamic pathways. ± 23 Therefore, it may be that the relationship with spinothalamic tract damage is limited to below-level neuropathic pain and should not be generalised to all types of neuropathic pain. The second issue is whether the development of pain is dependent on relative preservation of dorsal column pathways. Although this hypothesis has been proposed by Beric et al it does not enjoy such widespread support. As well as the ®ndings by Defrin and her colleagues, the relationship between neuropathic pain and preservation of dorsal column inputs has been questioned by others. Eide and colleagues systematically examined sensory function in a group of people with SCI. They found that although there was a signi®cant change in the mean thermal threshold in painful areas, the impairment of both spinothalamic and dorsal column function was not signi®cantly di€erent in painful denervated skin regions when compared with non-painful skin regions in people. Similarly, Bowsher found that although increased pain severity was associated with increased impairment of pin prick and thermal sensations, pain severity was not associated with di€erences in impairment of large ®bre function. Reports of pain in people with complete dea€erentation would also seem to go against this hypothesis. Some have argued that some patients may have preservation of transmission even though they appear to be clinically complete. However, this is questioned by the case series reported by Melzack and Loeser who described continuing neuropathic pain in a series of people with SCI who had veri®ed surgical cord transection. It is also questioned by reports of continuing neuropathic pain despite complete spinal local anaesthetic blockade above the level of injury. In summary, we agree that the bulk of evidence suggests that spinothalamic tract damage is an important and possibly essential ingredient in the development of neuropathic pain. However, while not disagreeing with the observations of Beric et al, there is no conclusive evidence that relative preservation of dorsal column inputs is a necessary prerequisite for the development of pain. Spinal Cord (2002) 40, 98 ± 99 ã 2002 International Medical Society of Paraplegia All rights reserved 1362 ± 4393/02 $25.00

DOI: 10.1038/sj.sc.3101246

Cite this paper

@article{Siddall2002InRT, title={In reply to Dr R Defrin et al}, author={PJ Siddall and J Loeser}, journal={Spinal Cord}, year={2002}, volume={40}, pages={98-99} }