Malignant spinal cord compression
Spinal cord compression (SCC) is commonly associated with cancers of the breast, prostate, and lung.1 It is not uncommonly associated with myeloma, lymphoma, renal cell carcinoma, and malignant melanoma. It is known, however, that SCC occurs in about 3-5 per cent of patients with any advanced malignancy and in 10-20 per cent of those with spinal metastases.2,3 In about 20 per cent, there is more than one level of compression.2 Box 1 shows the percentage of spinal levels involved at specific sites.
SCC commonly occurs following haematogenous spread of the malignancy. Spinal metastases result in initial expansion followed by destruction of the vertebral bodies and pedicles, and formation of an epidural mass which results in neurological compression.4 SCC can also result from the extension of an expanding or infiltrating paraspinal mass into the intervertebral foramina, such as may occur in lymphoma.
In pelvic malignancies such as carcinoma of the prostate, direct haematogenous spread via the Batson's vertebral venous plexus (an interconnected venous network surrounding the vertebral column) can result in cauda equina compression.
Clinical features and investigations
Severe, escalating backache, aggravated by coughing, sneezing, or any form of straining or attempted movement, often with associated radiculopathy pain (in a girdle or sciatic distribution), with point tenderness of the affected area of the spine are the earliest clinical features that imply an impending (or epidural level) spinal cord/cauda equina compression4 (See Box 2 for an example case scenario).
At this stage, the patient often has no sensory, motor, or sphincter dysfunction. However, they may describe 'funny feelings' in their legs, often compared to an electric current or cold water running down. Vigilance and a high clinical index of suspicion are absolutely essential. Sadly, many cases are still missed as the clinician waits for the classic neurological signs to appear.5 It is worth noting that a sensory level is not always present.1 If this is present, it can be a useful guide to the spinal level involved (See Box 3). For example, a sensory level at the umbilicus would indicate a lesion of the 10th dorsal vertebra.
A plain spinal X-ray often shows lytic or sclerotic metastases and/or collapse of vertebral bodies or destruction of pedicles in about 80 per cent of cases. An isotope bone scan will not help in the diagnosis of SCC. However, it can help to identify multiple sites of bone metastases.
An MRI of the spine provides the definitive diagnosis of SCC in virtually 100 per cent of patients affected (See Figures 1 and 2). MRI of the entire spine is recommended so as not to miss multiple levels of SCC, because these occur in about 20 per cent of patients.2 An MRI can also help to differentiate the malignant process from an infective process, because the disc is often affected in infection but not in malignancy.6-8