Cervical spondylotic myelopathy : a prospective study of outcome after surgery.

Abstract

Background: The natural history of cervical spondylotic myelopathy (CSM) is mixed. Surgical decompression is offered to patients with the aim of improving functional outcome. In some patients with chronic myelopathy, the aim is to prevent further deterioration. Despite surgical decompression, the functional status of some patients may deteriorate. CSM thus has a variable prognosis and it is difficult to predict neurological recovery after surgical decompression. There is a lack of consistency in the currently available literature regarding post-operative outcomes. Objectives: 1. To prospectively assess and compare the pre and post-operative clinical and functional status of patients with CSM using the modified Japanese Orthopaedic Association (mJOA) scores and the modified Myelopathy Disability Index (mMDI) scores at baseline, 3, 6 and 12 months post surgery. 2. To prospectively assess the natural history of patients with CSM who did not undergo surgery using the mJOA and mMDI scores at baseline, 3, 6 and 12 months. 3. To identify factors which influence outcome. Materials and Methods: All eligible patients in whom a diagnosis of CSM was made from 01 January 2011 to 31 December 2012 were evaluated. A neurologist (independent of the surgical team) performed baseline mJOA and mMDI scores. This was repeated at 3, 6, 12 and in some patients 24 months after surgery. Patients who refused or were not fit for surgery were also evaluated with mJOA and mMDI scores at baseline, 3, 6, 12 and in some, 24 months later by a 8 of 113 neurologist. These patients formed the natural history group. A minimum of 12 months follow up was obtained in all patients with a total of 540 months of follow up. The following factors were evaluated: age at presentation; gender; cigarette smoking; duration of symptoms; HIV status; presence of T2WI cord signal cord abnormality on MRI; number of cervical disc levels operated upon / affected; surgical approach used and post-operative complications. We also assessed recovery / progression of individual aspects of the mJOA: upper limb; lower limb; sensation and sphincters in both groups. Severity of CSM was assessed as mild if baseline mJOA score was ≥ 12 and moderate-severe if baseline mJOA score was < 12. Results: Surgery was associated with significant improvement in clinical recovery as assessed by mJOA scores at 3, 6 and 12 months post-operatively with p-values of 0.0002, 0.0001 and 0.0067 respectively. Upper limb function improved after surgery as assessed by the upper limb component of the mJOA score at 3, 6 and 12 months with p-values of 0.0096, 0.0030 and 0.0459 respectively. Lower limb function also improved significantly as assessed by the lower limb recovery scores at 3, 6 and 12 months with p-values of 0.0256, 0.0011 and 0.0107 respectively. Sensation and sphincter function did not improve after surgery. There was significant functional recovery as assessed by mMDI scores at 3, 6 and 12 months after surgery with p values of 0.0001, 0.0001 and 0.0023 respectively. There was no significant clinical or functional improvement in the non-surgical group when looking at overall mJOA and mMDI scores at 3, 6 and 12 months. Furthermore, there was no improvement in upper limb, lower limb, sensation or sphincter function in the non-surgical group as assessed by individual components of the mJOA score at 3, 6 and 12 months. 9 of 113 When assessing factors that could predict outcome we found that the patients’ age, gender, smoking status and duration of symptoms had no effect on outcome. The presence of T2WI cord signal abnormality on baseline MRI was associated with more severe CSM at presentation (p=0.036), but this did not affect outcome. Those with moderate-severe CSM at baseline had a better recovery at 12 months (p=0.025). The occurrence of intra-operative complications resulted in a worse outcome with both clinical and functional recovery rates worse at 3 months. Clinical recovery as assessed by mJOA score normalised at 12 months (p=0.235), but these patients were still functionally impaired as assessed by mMDI at 12 months (p=0.005). Conclusions: Patients with CSM benefit from surgical decompression regardless of baseline severity, with significant clinical and functional improvement noted at least 12 months post-operatively. Upper and lower limb function improves significantly, but sensation and sphincter function do not recover. The occurrence of intra-operative complications results in a worse outcome and this negative effect is still seen 12 months post-operatively. Patients who are managed non-operatively do not show significant improvement and 42% have some clinical deterioration at 12 months. Identification of patients with mild CSM (mJOA score ≥ 12) who can be safely managed non-operatively remains a challenge, however it appears that this is a reasonable option in patients with mild CSM and no T2WI cord signal abnormality on MRI.