Case 4. Progressive lower limb numbness
What is the lesion?
The key here - as ever - is the tempo, as well as the pattern of abnormalities seen. The latter has some anatomical relevance as certain processes are more likely to affect the dorsal columns - with the spine, 'Where?' influences 'What?'.
This is a chronic problem arising over months, so a wide variety of acute pathologies do not apply here such as ischaemia or inflammation (myelitis).
Metabolic disorders - particularly B12 deficiency - tend to cause a dorsal column disorder, although there is often associated neuropathy, which there is no evidence of in this case. In addition, such a clear sensory level is atypical.
Tabes dorsalis - dorsal column disease due to late-stage neurosyphilis - is an important consideration, and the incidence of syphilis is rising - although again the clear sensory level is atypical.
Compression is an important possibility here - whether due to an extrinsic or intrinsic process - and is a consideration in any spinal cord disorder.
This pattern - bilateral dorsal column dysfunction with spared motor and spinothalamic functions - isn't typical for degenerative disc prolapse, as that would tend to compress the anterior spine first (the discs are between the vertebral bodies, in front of the spine - and it is somewhat unusual to see this in the thoracic spine, in contrast to the cervical and lumbar regions where disc prolapse-related neurological disease is very common.
It is possible that other degenerative processes than discs could be active here however, although the pattern is atypical.
Tumours are a possibility, whether metastatic or primary - the vertebral column can be affected in metastatic cancers causing cord compression, while other tumours growing primarily in the central nervous system can include meningiomas, astrocytomas and ependymomas.
Of note, this patient has a history of breast cancer - and even though this was treated curatively, this does not give 100% protection against the possibility of later-stage metastatic disease. Unfortunately breast cancer has a real predilection for neurological metastasis, so any patient with a history of breast cancer - cured or not - who presents with neurological disease should always raise concern for metastasis.
In summary, this situation is concerning for a tumour affecting the spinal cord, quite likely compressing from the posterior aspect. Metastasis is a serious concern, and imaging is needed - but there are other tumours to consider, as above, even if this is not metastatic.
Clinical formulation