The relationship between an intramedullary high signal intensity and the clinical outcome in atlanto-axial subluxation owing to rheumatoid arthritis

Background contextIn patients affected by cervical spondylotic myelopathy (CSM), numerous authors have reported the existence of a relationship among the intramedullary high signal intensity in T2-weighted MRIs, preoperative neurologic severity, and neurologic recovery after surgery; however, to our knowledge, there have been no previous reports that have described its relationship in patients with atlanto-axial subluxation (AAS) owing to rheumatoid arthritis (RA).PurposeThe purpose of this study was to clarify the characteristics of patients with AAS owing to RA showing intramedullary high signal intensity in T2-weighted MRIs, and to assess the relationship with the neurologic severity and neurologic recovery after surgery.Study designThis was a retrospective cohort study.Patients sampleFifty consecutive patients (37 females and 13 males) with AAS treated by surgery were reviewed.Outcome measuresThe outcome was determined 1 year after surgery.MethodsAccording to preoperative T2-weighted MRIs, the patients were classified into two groups as follows: An NC group not showing any signal intensity change on sagittal images, and an SI group showing signal intensity changes with narrowing of the spinal cord. In all patients, we investigated the atlanto-dental distance (ADD) and the space available for the spinal cord (SAC) at the neutral position and the maximal flexion position in lateral cervical radiographs before surgery. We also observed MRIs 1 year after surgery in the SI group. We evaluated the severity of neurologic symptoms before and 1 year after surgery in all patients.ResultsPreoperative T2-weighted MRIs demonstrated NC in 38 cases and SI in 12 cases. The preoperative average ADD at the neutral position in the NC and SI groups was 6.4 and 10.2 mm, respectively (p<.01). The preoperative ADD at the maximal flexion position in the two groups were 10.8 and 13.8 mm, respectively (p<.01). The preoperative average SAC at the neutral position in the NC and SI groups were 17.6 and 13.8 mm, respectively (p<.01). The SAC at the maximal flexion position in the two groups were 14.3 and 10.8 mm, respectively (p<.01). The SI group included significantly more Ranawat grade III cases showing severe neurologic deficits compared to the NC group (p<.01). However, there were no differences between the two groups regarding the number of patients with Ranawat grade III status after surgery (p>.65). On MRIs 1 year after surgery, the regression or disappearance of the signal intensity change in T2-weighted images was demonstrated in four and seven cases, respectively.ConclusionsPreoperative ISHI in T2-weighted MRIs in RA-induced AAS patients was demonstrated in patients showing an enlargement of the ADD and a narrowing of the SAC. This affected the preoperative neurologic severity, but not the postoperative severity, which was in contrast to CSM patients. Furthermore, the regression or disappearance of ISHI was demonstrated in all of the cases after surgery. It is therefore speculated that RA AAS patients may have both dynamic instability and stenosis.