Radiation injury of the spinal cord

Relationship between Curative Radiation Therapy of Paravertebral Tumors and the Incidence of Radiation Myelitis

The literature about radiation damage to the spinal cord is reviewed and 4 of own cases are presented. It is pointed out that in curative radiation therapy the risk of myelitis that accompanies higher spinal cord doses must be weighed against the therapeutic gains. However, in view of the lack of information about radiation damage to the spinal cord, this may be quite difficult.

Autopsy verifies demyelination and lack of vascular damage in partially reversible radiation myelopathy

STUDY DESIGN

Case report of recovering radiation myelopathy.

OBJECTIVE

To present autopsy and functional imaging findings on a unique case of slowly recovering radiation myelopathy with the aim of the clarification of the underlying mechanism.

PATIENT

The cervical spinal cord and the distal part of the medulla oblongata of a 36-year-old thyroid cancer patient had been incorrectly irradiated with a total dose of 61 Gy and a fraction size of 3.4 Gy (J Neurol Sci 1999; 163:39-43), resulting in incomplete cervical transection with a 5-month latency period following the termination of radiotherapy. This was followed by a 9.5-year spontaneous improvement until her demise, during which the check-ups were supplemented by positron emission tomography (PET) investigations; these indicated increased [18F]deoxyglucose and [15O]butanol uptakes, but a diminished [11C]methionine accumulation by the irradiated spinal cord segment.

RESULTS

Autopsy revealed demyelination (with axonal loss) and neuronal damage in the cervical spinal cord and the distal part of the medulla oblongata. In the same region, only minimal vascular injury (thickening of some of the capillary walls) was detected, but not cell proliferation or chronic inflammation. Bilateral, secondary pyramidal tract degeneration caudal to the irradiated segment was observed. The PET and autopsy findings, although separated by 2 years, are consistent.

CONCLUSIONS

The pathological state of the spinal cord revealed by the autopsy is concordant with the incomplete cervical transection, implying that the functional recovery is supported by a process that probably differs from the restoration of the mechanism destroyed by the radiotherapy. For the restoration of the function, we suggest an altered conduction mechanism of the action potential, involving an increased number of sodium channels along the demyelinated segments of the injured axons, which is fully congruent with the PET findings.

A review on radiogenic Lhermitte's sign

Radiation myelopathy is a rare, but extremely serious side-effect of radiotherapy. Recovery from radiation-induced motor sequelae is rare, whereas, the regeneration of sensory losses is relatively frequent. Among the sensory radiogenic injuries of the spinal cord, Lhermitte's sign (LS) is most frequent. This review describes the clinical picture and diagnostic imaging signs of radiogenic LS. There have been only a few studies on large patient groups with radiogenic LS, demonstrating a rate of occurrence of 3.6-13%, relating mainly to mantle irradiation or the radiotherapy of head and neck tumors. These cases typically manifest themselves 3 months following radiotherapy and gradually disappear within 6 months. Only 3 LS cases have been described in the English literature with extraordinarily severe symptoms lasting for more than 1 year. MRI, a sensitive tool in the detection of demyelination, failed to reveal any pathological sign accompanying radiogenic LS. However, positron emission tomography demonstrated increased [18F]fluorodeoxyglucose accumulation and [15O]butanol perfusion, but a negligible [11C]methionine uptake in the irradiated spinal cord segments in patients with long-standing LS. These imaging data are suggestive of a close direct relationship between the regional perfusion and metabolism of the spinal cord, very much like the situation in the brain. We postulate that an altered, energy-demanding conduction along the demyelinated axons of patients with chronic radiogenic LS may explain the increased metabolism and perfusion.

A PET study on the characterization of partially reversible radiogenic lower motor neurone disease

OBJECTIVE

To investigate the pathomechanism of the rare radiogenic lower motor neurone disease (LMND) on the basis of a case history involving a partial functional recovery.

PATIENT

A 31-year-old seminoma patient received postoperative para-aortic and para-iliac telecobalt irradiation with a biologically effective dose of 88 Gy(2) (44 Gy in 2 Gy fractions/day, with an estimated alpha/beta of 2 Gy) delivered to the spinal cord following a single cycle of chemotherapy. LMND developed 4 months after the completion of radiotherapy. The patient exhibited flaccid paraparesis of the lower extremities (without sensory or vegetative signs), followed by a worsening after further chemotherapy, due to pulmonary metastatization. A gradual spontaneous functional improvement commenced and led several years later to a stabilized state involving moderately severe symptoms.

METHODS

In the 15th year of the clinical course, magnetic resonance imaging (MRI) and positron emission tomography (PET) with [(18)F]fluorodeoxyglucose (FDG) and [(11)C] methionine were conducted. Four lines of experiments (clonogenic assay using fibroblasts isolated from a skin biopsy sample of the patient, comet assay, micronucleus assay, and the testing of chromosome aberrations after in vitro irradiation of peripheral blood samples) were performed in a search for an increased individual radiosensitivity.

RESULTS

MRI investigations failed to reveal any pathological change. PET demonstrated an increased FDG accumulation, but a negligible [(11)C] methionine uptake in the irradiated spinal cord segments. The radiobiological investigations did not indicate any sign of an increased individual radiosensitivity.

CONCLUSIONS

We suggest that the observed partial functional recovery and stabilization of the symptoms of radiogenic LMND may be explained by the higher than normal density of sodium channels expressed along the demyelinated axons of the restored conduction. The increased energy demands of this type of conduction are proved by a higher metabolic rate (increased FDG uptake) of the irradiated spinal cord segments without a substantial regenerative process (lack of detectable protein synthesis).

Radiation myelopathy with partial functional recovery: PET evidence of long-term increased metabolic activity of the spinal cord

Postoperative telecobalt irradiation was performed with a biologically effective extrapolated response dose of 165 Gy2 delivered to the spinal cord of a papillary thyroid cancer patient. Incomplete cervical transection developed, followed by a gradual functional improvement, which is still continuing 8 years after radiotherapy. Between the 6th and 8th years of the clinical course, positron emission tomography investigations demonstrated an increased 18F-deoxyglucose accumulation and (15)O-butanol perfusion, but negligible 11C-methionine uptake in the irradiated spinal cord segment. We suggest that the increased metabolism and perfusion, and the lack of detectable protein synthesis may be related to the increased energy demands of action potential conduction, due to the higher than normal density of sodium channels along demyelinated axons displaying restored conduction.

The effect of single doses of radiation on mouse spinal cord

We have used a mouse model to study spinal cord injury following single doses (12 to 75 Gy) of radiation. The spinal cord (T9,10-L4,5) of C3Hf/Sed//Kam mice was irradiated and response graded using four levels of neurological change. Findings were: (a) the doses required to paralyze 50% of animals (ED50) were 19.79, 20.77, and 21.85 Gy for mild, partial, and complete paralysis, respectively, as measured 200-360 days after radiation. (b) Most damage was progressive but it was not necessarily so; after doses up to 28 Gy recovery was occasionally seen. (c) Latency depended on the dose and the level of damage. Following doses around the ED50, paralysis occurred between 180 to 300 days. (d) There were significant fluctuations in the dose-latency relationship at doses less than 35 Gy. Latency may be not a reliable endpoint to compare biological effects of radiation in this dose range. (e) The radiosensitivity of mouse spinal cord was similar to that reported for rats. (f) Histologically, demyelination was the dominant lesion in the paralyzed animals. We conclude that the mouse is a good animal model to study radiation damage to the spinal cord, at least when a 2.2 cm length is irradiated.

The latent period in clinical radiation myelopathy

Seventy-seven papers containing data on more than 300 cases of radiation myelopathy have been analyzed. The data suggest that the latent periods are similar in the cervical and thoracic levels of the spinal cord and are bimodally distributed. Myelopathy of lumbar cord apparently has a shorter latent period. As in controlled animal experiments, the latent period decreases with increasing dose. Furthermore, the variation in latent periods also decreases with dose. It is also seen that retreated patients and pediatric or adolescent patients have greatly reduced latent periods. The implications of these findings as they compare with the animal data are discussed.

Dose effect relationships in cervical and thoracic radiation myelopathies

The course and prognosis of radiation myelopathies are determined by 3 factors; the segmental (vertical) location of the lesion, the extent of the transverse syndrome (complete or incomplete) and the radiation dose. The median spinal dose in cervical radiation myelopathies with fatal outcome was higher than in survivals with an incomplete transverse syndrome. In thoracic radiation myelopathies a dose difference between complete and incomplete transverse syndromes could be found as well. Incomplete transverse syndromes as submaximum radiation injuries are more suitable for the determination of the spinal tolerance dose than complete transverse syndromes. The lowest threshold could be stated for cases following high-volume irradiation of the lymphatic system.

Radiation myelopathy in children

Three children, 1 with medulloblastoma, 1 with anaplastic cerebellar tumor, and 1 with acute lymphocytic leukemia, received craniospinal irradiation with an estimated cord dose between 1,100 and 1,200 rets. All 3 patients after a latent period of seven to eight months developed subacute transverse myelopathy. The myelopathy was cervical in 2 patients and thoracic in 1. Spinal fluid examination showed high protein levels in 2 patients. Myelography demonstrated a swollen cord in 2 patients and normal appearance in 1. Autopsy in 1 patient disclosed a necrotizing myelopathy. The findings suggest that children tolerate less well than adults what previously have been considered safe doses of radiation to the spinal cord.

Radiation myelitis following craniospinal irradiation with concurrent actinomycin-D therapy

Two patients are presented who developed radiation myelitis as a complication of treatment for medulloblastoma. These patients had been entered onto a pilot study to evaluate the therapeutic efficacy of combined treatment with radiation therapy and actinomycin-D (AMD). AMD is a known radiation enhancer in all tissues but the nervous system. Both of these patients received a full course of cranio-spinal irradiation plus AMD 15 mcg/kg for the first five days of therapy. One patient developed myelitis at 4 months, and the other at 12 months after treatment. Both patients are surviving three years posttreatment without any evidence of recurrent disease. The myelitis in one patient has improved, and it is stable in the other patient. It is concluded that AMD enhances the effect of radiation therapy on the central nervous system. This has never been reported but is important to note now, since radiation enhancers are included in multimodal treatment regimens for a variety of malifnant conditions. Reduction of radiation dose may be necessary when large volumes of the nervous system are treated.

Neurologic complications after irradiation of malignant tumors of the testis

Of 156 consecutive patients with malignant tumor of the testis 99 were alive two years after treatment. Of these, 12 had radiation-induced neurologic complications which, in 5 instances, consisted of persisting, wholly or partially disabling paresis in the lower limbs. Five had mild, transient symptoms and had persisting symptoms which were not incapacitating. In all those with disabling symptoms the irradiation dose had been higher than 1 600 reu, corresponding to 54.5 Gy over 6 weeks with daily fractions 5 days a week.

Parathyroid hormone and calcitonin in serum of patients with mammary carcinoma

Immunoreactive parathyroid hormone and calcitonin in serum were measured in 34 normocalcemic patients with mammary carcinoma. The mean value of parathyroid hormone was significantly higher in 26 patients with bone metastases than in 8 patients without (p less than 0.025). One patient with bone metastases had slightly raised calcitonin in serum. No difference as to parathyroid hormone values between the groups of previously irradiated and non-irradiated patients was found. A possible explanation of the normocalcemic hyperparathyroidism is presented.

Late sequelae of radiation therapy in cancer of the head and neck with particular reference to the nasopharynx

Sequlae of radiation therapy may be late in occurring and varied in their manifestations. Although some are untreatable and progressive, the risk of development of some other sequelae can be minimized by careful application of radiotherapy or by ancillary measures, such as dental decay prophylaxis. Some of the serious sequelae secondary to radiation therapy of the nasopharynx have been summarized. These include radiation myelitis, paralysis of the cranial nerves, stricture of the pharynx, radiation-induced cancer, and necrosis with fatal hemorrhage.

Angiography of the spinal cord. A review of contemporary techniques and applications

✓ The authors present a current review of the development, techniques, and applications of angiographic studies of the spinal cord, with special emphasis on selective arteriography.