Clinical Features of Thoracic Myelopathy: A Single-Center Study

Introduction: Thoracic myelopathy is relatively uncommon because few degenerative changes occur as a result of the restricted range of motion surrounding the rib cage. Methods: A retrospective study was performed in 300 consecutive surgical cases of thoracic disorders with myelopathy treated in our department from 2000 to 2015. Girdle pain, back pain, low back pain, leg numbness, leg pain, gait disturbance, leg paresis, and bowel bladder disturbance as initial and preoperative symptoms; patellar tendon reflex, ankle tendon reflex, and ankle clonus as preoperative neurologic findings; MRI and CT findings; and surgical procedure, intraoperative findings, and postoperative recovery were investigated. Results: The disease distribution included ossification of the ligamentum flavum (OLF) (n = 48), ossification of the posterior longitudinal ligament (OPLL) (n = 30), OPLL with OLF (n = 27), intradural extramedullary tumor (n = 98), intramedullary spinal cord tumor (n = 64), vertebral tumor (n = 17), spinal cord herniation (n = 7), vertebral fracture (n = 4), and thoracic disk herniation (n = 5). There were notable associations of gait disturbance with OPLL and OPLL + OLF; back pain at initial diagnosis with disease at upper levels; and low back pain with disease at a lower level. Conclusion: These findings suggest that patients with gait disturbance, back pain, and low back pain on physical examination may have thoracic disease that results in myelopathy.

symptoms mimic those of cervical or lumbar spinal disorders, and thus, thoracic myelopathy is often overlooked in a search for a cervical or lumbar etiology, which can result in delayed treatment. 6,7Misdiagnosis can also lead to a prolonged preoperative disease duration, which can result in myelopathy and cause irreversible neurologic damage. 2 However, the characteristics of thoracic myelopathy have not been adequately addressed because of the low prevalence and the small number of patients treated surgically. 2 Knowledge of the symptoms of thoracic myelopathy is important for early diagnosis and treatment.Therefore, in this study, we examined symptoms and physical examination findings associated with diseases that cause myelopathy at each level of the thoracic spine, with the goal of identifying factors that are associated with these diseases.

Methods
A retrospective study was performed in 300 consecutive cases of thoracic disorders with myelopathy treated at our department from 2000 to 2015 (Table 1).The study was approved by the institutional review board of our university.
The severity of myelopathy before and after surgery was evaluated using the Japanese Orthopaedic Association (JOA) score for thoracic myelopathy (total of 11 points), which was derived from the JOA score for cervical myelopathy by eliminating the motor and sensory scores for the upper extremities. 8,9Postoperative improvement of symptoms was evaluated using the % recovery of the JOA score and the   Girdle pain, back pain, low back pain, leg numbness, leg pain, gait disturbance, leg paresis, and bowel bladder disturbance (BBD) as initial and preoperative symptoms; patellar tendon reflex (PTR), ankle tendon reflex (ATR), and ankle clonus as preoperative neurologic findings; MRI and CT findings; and surgical procedure, intraoperative findings, and postoperative recovery were investigated.T1-4 was defined as the upper level, T5-8 as the middle level, and T9-12 as the lower level.The follow-up period was a minimum of 1 year.
Data were analyzed using SPSS ver.22 (IBM SPSS Statistics 19.0; IBM).Data are presented as mean 6 SD.Radiographic parameters and clinical data from 2 groups were compared by the Student t-test.Multivariate logistic regression analyses were used to calculate the odds ratios (ORs) and 95% confidence interval (CI) to identify factors associated with disease or affected level.P , 0.05 was considered significant.

Discussion
Thoracic disease with myelopathy is relatively rare, and diagnosis may be delayed. 10The disease can be diagnosed by MRI and CT, 11 but criteria are based on limited reports with relatively few patients with thoracic  ossification, spondylosis, and disk herniation. 1,2In this study, we included other disorders that are causes of thoracic myelopathy, including spinal tumor, spinal cord tumor, trauma, ossification of the ligament, and SCH, in addition to these diseases, and we identified factors associated with these diseases by comparing symptoms and physical examination findings.
The mean disease duration of IMSCT and SCH tended to be longer than that for other diseases.These diseases are rare, [12][13][14] and the period until surgery may reflect the longer time required for diagnosis.Similarly, the shorter disease durations of VT, VF, and TDH may be linked to their relative ease of diagnosis using radiograph, MRI, and CT. 15,168][19] The reasons for the high frequency of OLF at lower thoracic levels include increased mechanical stress where the thoracic vertebrae form the junction between the rigid rib cage and elastic lumbar spine, a direct correlation between increased mobility of the spine and repetitive mild trauma, and high tensile force present in the posterior column. 17Matsumoto et al 20 analyzed the surgical outcomes of patients with thoracic OPLL and found an average recovery rate of 36% and reduction of myelopathy immediately after surgery in 12% of patients.As preoperative myelopathy became severe, the JOA recovery rate became worse.It is generally considered that PTR and ATR were hyper in patients with myelopathy.However, hyper-PTR, and positive ankle clonus occurred less frequently at the lower level in this study.The low rate of hyper-PTR, hyper-ATR, and positive ankle clonus may be explained by the involvement of conus and lumbar nerve roots. 21We should be aware of the possibility of lower thoracic diseases without hyper-PTR and hyper-ATR in thoracic myelopathy.
The number of symptoms just before surgery was higher than the number of initial symptoms.Moreover, an increase in the rate of change in preoperative symptoms compared with initial symptoms such as leg numbness, gait disturbance, leg paresis, and BBD was notably higher than that of girdle pain, back pain, and low back pain.In other words, it might mean the finding of increased neurologic compromise with no clear increase in the pain level at the time of surgery compared with the time of the initial diagnosis.
Gait disturbance at initial diagnosis, including leg palsy, leg numbness, posterior column ataxia, and spasticity, was notably associated with OPLL and OPLL 1 OLF.These are generally severe conditions because of spinal cord compression from the anterior or posterior side, which results in various symptoms.Gait disturbance is a representative symptom for patients with thoracic ossification. 22Back pain at initial diagnosis was notably associated with disease at the upper and middle levels, whereas low back pain was linked to disease at the lower level.The high prevalence of low back pain in patients with lower level disease may be explained by the involvement of the conus, which is a target for treatment of low back pain. 23,24Several case reports have indicated a relationship of back pain with upper and middle level disorders, 25,26 and we speculate that a change in pressure in the spinal cord and vertebral column could lead to back pain.
To the best of our knowledge, this is the first report to examine factors related to diseases and levels that result in thoracic myelopathy.It was suggested that the increased neurologic compromise at the time of surgery compared with the time of the initial diagnosis was not associated with the pain level.Gait disturbance at initial diagnosis was associated with OPLL and OPLL 1 OLF.Back pain at initial diagnosis was associated with disease at the upper and

Conclusion
We examined the characteristic factors related to diseases at each level of the thoracic spine that can result in myelopathy, based on symptoms and physical examination findings.We should be aware of the possibility of lower thoracic diseases without hyper-PTR and hyper-ATR in thoracic myelopathy.The increased neurologic compromise at the time of surgery compared with the time of the initial diagnosis was not associated with the pain level.OPLL and OPLL 1 OLF were characterized by gait disturbance at initial diagnosis.Back pain at initial diagnosis was associated with upper and middle level disease, and low back pain was linked to lower level disease.Bar graph showing that back pain at initial diagnosis with disease at a upper level and low back pain with disease at a lower level were significantly higher than another pain; #P , 0.01.

Table 1
Summary of Demographic Data in 300 Patients With Thoracic Myelopathy

Table 3
Patients' Demographics for Each Disease VF, and TDH compared with other diseases.The preoperative JOA score was lower in OPLL 1 OLF and SCH.OLF occurred at a lower level, and OPLL and OPLL 1 OLF were found at a middle level most frequently.The JOA recovery rate was lower in OPLL, OPLL 1 OLF, and IMSCT (Table3).

Table 3
Patients' Demographics for Each Disease

Table 4
Patients' Demographics for Each Affected Level

Table 5 Factors
Related to Disease Based on Multiple Logistic Regression Analysis = ossification of the ligamentum flavum, OPLL = ossification of the posterior longitudinal ligament middle levels, whereas low back pain was linked to disease at the lower level. OLF

Table 6
Factors Related to Affected Level Based on Multiple Logistic Regression Analysis