Central Nervous System
Spinal cord damage (Radiation Induced Myelopathy)
Two types of radiation myelopathy:
Early/Transient Radiation Myelopathy |
Delayed Radiation Myelopathy |
Occurs 6 weeks-6 months following the onset of radiation
Symptoms are usually mild and recovery is anticipated in 2-9 months
Characterized by L’Hermitte’s sign – a sensation of an electric shock upon neck flexion |
Occurs in 1-12.5% of patients with radiation doses >6000 cGy and fraction size >200 cGy
Occurs month to years following radiation therapy
Characterized by acute or progressive paraplegia or quadriplegia, loss of bowel/bladder function
Demyelination with loss of axons and spinal cord necrosis is seen on autopsy
Vascular changes including endothelial thickening, vasculitis, telangiectasia, fibrinoid necrosis and perivascular fibrosis is also seen |
Risk factors for radiation induced myelopathy:
- Higher RT total dose
- Higher RT fraction size
- Shorter overall treatment time
- Shortened intervals between treatments
- Length of spinal cord in the treatment volume
- Risk is increased if more than 10 cm is treated
However, there is no evidence to show that one section of the spinal cord is more sensitive to RT than others
Imaging:
- Spinal cord swelling, demyelination and necrosis is best seen on MRI.
- CT scans are generally not helpful
- MR shows:
- Cord swelling or atrophy
- Decreased intensity on T1-weighted images
- Increased intensity on T2-weighted images
Other investigations:
Increased levels of myelin basic protein released into CSF with focal or diffuse demyelination.
Therapy
Treatment of radiation myelopathy is rarely if ever successful
- Corticosteroids (intensive intravenous schedule) given initially to reduce edema:
- 10 mg intravenously of dexamethasone (Decadron) for 1 day
- Dose is then tapered to stabilize progress
Anticoagulation may prevent further damage and may reverse damage to endothelium of small blood vessels (but no clear evidence to support this).
