Thoracic spinal cord compression due to excessive scarring around surgical paddle epidural electrodes. Report of two cases with literature review

Introduction
Spinal cord stimulation (SCS) is considered an efficient and safe method of treating intractable chronic pain from various origins such as persistent spinal pain syndrome (PSPS) or complex regional pain syndrome (CRPS). The complications related to SCS therapy are usually classified as mechanical or biological. Myelopathy related to dense scar tissue formation around epidural paddle electrodes implanted for SCS therapy is extremely rarely reported. We have studied all reported cases of surgical management of this complication and we sought to find predisposing factors responsible for development of this rare but dangerous complication.

Case summary
We report on 2 cases of thoracic spinal cord compression by scar tissue encountered around epidural electrodes implanted for SCS. Both patients had their implantable pulse generators (IPGs) removed due to biological complications (skin erosions with subsequent infection at IPG site confirmed in one patient). During the waiting time for further placement of new IPGs, both patients developed myelopathic symptoms. Magnetic resonance imaging (MRI) in both cases showed severe compression of the spinal cord by scar tissue around the electrode. Surgical decompression resulted in full and partial recovery in each patient. In both cases, during surgery, excessive epidural fibrosis was encountered, without signs of active infection. Surgical decompression in patient 1 resulted in full recovery, while patient 2 had a complicated postoperative course with partial recovery.

Conclusions
To our knowledge, both cases constitute extremely rare complications of SCS therapy resulting in thoracic spinal myelopathy. The predisposing factors found in our patients were surgically placed paddle electrodes with a prior history of IPG removal due to biological complications (skin erosions and infection). In the literature, surgical electrodes placed in the cervical spine rather than the thoracic spine were more often found to result in excessive epidural scarring, resulting in spinal compression syndromes. Prompt surgical decompression with scar tissue removal is mandatory to achieve full recovery.