Why is ASCC relevant to Degenerative Cervical Myelopathy?
Asymptomatic spinal cord compression (ASCC) is very common; studies of healthy volunteers has identified between 8 and 59 in every 100 patients who underwent a cervical MRI had it!  These are the same compression features seen in DCM, however less that 1 in a hundred patients from these studies had any symptoms of myelopathy…. Hence the term ASCC (as opposed to DCM, which is defined by the symptoms of the condition, such as pain and weakness).
However, we know from other studies that some people with ASCC go onto develop DCM over time and this has led to the suggestion that ASCC actually represents the earliest stages of DCM. In order to further evaluate this, researchers from North America have been using new MRI imaging techniques to better understand asymptomatic cord compression and to see whether the compression is affecting the spinal cord.
What was the aim of the study?
The study, undertaken at the University of Toronto had two primary aims:
1)Can ASCC be automatically diagnosed by using computer analysis of MRI images?
2)Can damage to the spinal cord be visualised using new MRI techniques in ASCC?
How did they measure subclinical damage and cord compression?
The group recruited 40 individuals to the study, 20 of which has ASCC and 20 had no evidence of cord compression.
Aim Number 1
The performance of a computer programme to diagnose cord compression was compared to a group of experts and found to be just as good.
Aim Number 2:
The group then compared people with and without ASCC using a number of new techniques to look at the structure within the spinal cord, these include the following
The researchers found that some of these new imaging techniques were able to detect changes within the ASCC group that are also seen in DCM; specifically, FA, MTR and T2*WI WM/GM. When compared to uncompressed individuals, a combined score looking at a combination of parameters was very accurate at spotting tissue injury. This indicated that there is a degree of tissue damage before symptoms in ASCC, and that this perhaps represents the early stage of degeneration that progresses into degenerative cervical myelopathy.
What to make of this?
This study is informative to clinicians, as it reflects a way to diagnose ASCC early on before significant damage has been done to induce symptoms. The success of the computer diagnosis also means ‘expertise’ can be transferred into any hospital setting. This is exciting, as we know that if we could detect DCM earlier, and offer treatment sooner, patients would make a better recovery.
The finding that ASCC causes tissue damage also may make us question our definition of myelopathy. Currently, symptoms are the definitive characteristic of myelopathy, but as advances in technology allow us to detect spinal cord damage in the absence of symptoms, this may change. The symptoms of myelopathy may reflect a later stage of damage that occurs after what we can now see using MRI.
Furthermore, the findings of similar tissue injury in ASCC to DCM indicated a possible definitive link between the two disease states. The researchers compare the two as being similar to “pre-diabetes” and “diabetes” (a scenario where people who are struggling to handle their blood sugars are identified even earlier, with some able to make changes to prevent the onset of diabetes). Perhaps what we are seeing here is a “pre-DCM” state. This still requires more work to be confirmed. We look forward to following the research story further!
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