RADT-48 - Radiation myelopathy after standard dose radiation: potential radiation sensitizing effects of systemic therapy  

Radiation myelopathy is an uncommon adverse effect of spinal irradiation. It is especially rare following conventional palliative fractionation regimens for vertebral metastasis. We present two cases of delayed thoracic radiation myelopathy in patients with breast cancer. In both cases, palliative radiation of 30 Gy in ten fractions was administered to thoracic spinal metastases. Neither patient received concurrent systemic therapy. One began trastuzumab emtansine nine days after finishing radiation and the other started palbociclib three months afterwards, which was switched to capecitabine at disease progression. Each patient developed progressive leg weakness and numbness, ten months following radiation and eleven months following radiation (four weeks following capecitabine), respectively. MRI showed edema and focal contrast enhancement within the radiation field in each. Both were treated with high-dose corticosteroid, vitamin E, and pentoxifylline. Neither patient returned to their neurologic baseline and remain with significant deficits, requiring assistance with ambulation. Serial MRIs revealed eventual reduction in cord enhancement and edema, followed by cord atrophy in one case. The cumulative radiation dose of 30 Gy is typically within the safety tolerance of the spinal cord, so it is speculative if post-radiation systemic therapy played a role in the development of myelopathy. The timing is particularly convincing in the patient who developed symptoms within four weeks of starting capecitabine. These cases are similar to recently reported instances of radiation myelopathy after standard dose spinal radiation followed by chemotherapy or immunotherapy. Recognition of the potential radiation sensitizing effects of systemic therapy should lead clinicians to consider radiation myelopathy early if spinal cord symptoms develop and to consider the timing of initiation of potential sensitizing drugs when spinal radiation has been given.