Treatment may depend on the patient's prognosis. Treatment is advised if the patient is expected to recover or possibly live longer by having treatment. Sometimes quality of life is improved enough that the treatment (with its possible side effects) is still more beneficial than not having treatment.
Radiation has been shown to help stop the destruction of bone in the cervical spine from multiple myeloma metastases. In fact, there are case reports of reversal of the bone destruction. X-rays show fractures heal and bone remodeling can occur with radiation alone.
In some cases, surgery may be needed to stabilize the spine. Spinal fusion may be needed. But since radiation alone has been so effective, this is the first step. The next step (if any is needed) is based on the patient's response to the treatment and results at the bony level as seen on X-ray.