Prostate Cancer and Spinal Cord Compression
Prostate Cancer and Spinal Cord Compression
Prostate cancer is the second leading cause of cancer death in men in the United States. Between 1% and 12% of men with adenocarcinoma of the prostate will develop spinal cord compression. Dr. Chen has presented an excellent overview of a difficult clinical problem. At the risk of oversimplification, the patient is generally an older male presenting with back pain, with or without neurologic involvement. If the patient has been diagnosed with prostatic adenocarcinoma, the assumption is that he has metastatic disease of the spine, and this may indeed be the case. The advanced age of these men, however, predisposes to multiple other comorbidities. Other tumors may be present, immunosuppression may have predisposed to spinal column infection, hormonal ablation may have caused an osteoporotic compression fracture, or previous spinal irradiation may lead to avascular necrosis of the vertebral body.
Metastatic prostate cancer has a predilection for the thoracic spine. Although Batson’s plexus may be the conduit through which carcinoma cells gain access to the vertebral column, I hold to the somewhat simplistic theory that tumor expression in the spinal column is based on the availability of vertebral bone marrow. Because the thoracic spine is the largest segment of the vertebral column, it offers the most vertebral sites for implantation of cancer cells.
I agree with Dr. Chen’s algorithm for a diagnostic work-up and strongly support his concept of total investigation of the spine in light of the known incidence of multiple, discreet lesions in prostatic carcinoma, as well as the possible problems.
Traditionally, surgery for spinal metastases has had three roles:
decompression to remove mechanical compression of the spinal cord or cauda equina
What If It Isn’t Metastatic Spinal Disease?
In this older population of men who present with pain, we have to be certain that any abnormalities seen on imaging studies truly represent metastatic disease. Magnetic resonance imaging (MRI), x-ray, computed tomography (CT) scanning, and bone scanning all provide useful information, but often a CT-guided biopsy under local anesthesia will provide an accurate and rapid diagnosis. Establishing a specific etiology for a spinal lesion is important in that now there are very specific treatments for the different causes of spine pain. For example, kyphoplasty is gaining acceptance for use in osteoporotic fractures and certain malignancies. The procedure involves a percutaneous injection of bone cement into the vertebral body, thus allowing simultaneous bone biopsy and restitution of vertebral body height and stability. This can be performed over multiple levels in the spine, and is often effective in restoring alignment and providing pain relief. We must assume that we are not curing but only ameliorating the symptoms of spinal metastatic disease and, to that end, kyphoplasty may have a significant advantage over open surgical procedures.
In spinal cord compression, radiation is often the first course of treatment. Unfortunately, radiation will have no beneficial effect and may be contraindicated in patients with spinal instability, cord compression related to bone and not soft tissue, and preexisting spinal stenosis. In these cases, radiation may delay appropriate treatment and may predispose to soft-tissue breakdown and sepsis if surgery is ultimately performed. Likewise, many patients have already received maximal radiation to the area in question.
Limitations of Laminectomy
As Dr. Chen states, the earlier literature on surgery for metastatic disease usually suggested laminectomy as the procedure of choice. Posterior laminectomy is often contrary to Sutton’s Law: "Go where the money is." Although laminectomy is useful when there is a mechanical block in an otherwise stable spine, the vertebral body itself is often the site of metastatic disease and the tumor mass is anterior to the cord. Laminectomy removes the only stable portion of the spinal column and often worsens the clinical situation.
If there is instability, laminectomy must be combined with posterior stabilization via pedicle screws or various hook/rod constructs. Surgical stabilization of the spine can obviate the need for bracing and allows immediate mobilization. If cord compression is anterior to the spinal cord, an anterior decompression and stabilization may be considered. The spine can be stabilized with an anterior allograft spacer or a titanium cage packed with autologous bone. Radiation must be deferred for at least 3 weeks after a front or back fusion procedure so as to increase the opportunity for bone incorporation and decrease the opportunity for soft-tissue breakdown and sepsis.
Unfortunately, treatment options present ethical and therapeutic dilemmas. We are typically dealing with patients who are older and who have other comorbidity. Usually, the extent of the systemic disease and comorbidity will determine how aggressive the surgeon may or may not be. I agree with Dr. Chen’s statement that there are no correct answers as to how any individual patient should be managed. Consultation among surgeon, oncologist, radiation therapist, gerontologist, patient, and family is mandatory. It is important that everyone fully appreciate the potential risks of surgery, specifically taking into account age and comorbidity. It is also important that the goals of surgery are well appreciatedie, we are hoping to ameliorate pain but, in all likelihood, will not cure disease and may not cure severe neurologic defects.
I greatly appreciate Dr. Chen’s algorithms and his emphasis on the fact that the treatment plan must be multidisciplinary and considered a work in progress. Postoperatively, there probably is a place for long-term treatment with bisphosphonates to help increase bone mass and prevent late osteoporosis and osteoporotic fractures.