Clinical considerations for non-operative treatment of spinal metastases with intermediate instability.

Aims: To investigate the characteristics of spinal adverse events after non-operative treatment for spinal metastases with intermediate instability and to discuss clinical considerations when selecting non-operative treatment.

Methods: This study included 56 patients with spinal metastases who had Spinal Instability Neoplastic Scores (SINS) of 7-12 and who underwent radiotherapy and intensive rehabilitation without a bed rest period as initial treatment between 2020 and 2023. We evaluated progression of paralysis and changes in spinal alignment before treatment, within 1 month, 1 to 6 months, and more than 6 months after treatment.

Results: Paralysis progressed within 1 month after treatment in 7 of 56 patients (12.5%). Pre-treatment paralysis and SINS ≥ 11 were significantly associated with progression of paralysis. Alignment changes occurred in 18 of 56 patients (32.1%), with a similar incidence in patients with SINS ≥ 11 and ≤ 10. Fifteen of 44 patients (34.1%) without pre-treatment paralysis had alignment changes, but 1 patient (2.3%) experienced progression of paralysis due to increased instability within 1 month. All 3 patients whose paralysis progressed despite no evidence of malignant spinal cord compression before or after treatment had SINS ≥ 11 and showed vertebral height reduction and kyphosis progression within 1 month.

Conclusion: Patients with pre-treatment paralysis and SINS ≥ 11 can progress to paralysis early; therefore, careful observation and imaging examinations are recommended early after treatment. If spinal alignment worsens, the treatment plan should be reconsidered, including restrictions of activity and surgical treatment.