X-IRRADIATION AND DELAYED MYELOMALACIA 241 



malacia. This is related to the well known irradiation damage which affects 

 the marrow of the surrounding vertebrae. 



Two rats that showed no clinical signs were killed at 7 and 9/2 months 

 after irradiation, and small lesions (Fig. 6) were found in the white matter 

 at an early stage of development. 



Severe myodegeneration and necrosis of the veitebral skeletal muscles in 

 the same area as the spinal cord damage was almost a constant concomitant 

 finding (Figs. 7 A and 7B). Such changes have not been reported in experi- 

 mental studies by others or in human cases of postirradiation myelopathy. 



Experimental work on x-irradiated monkeys 



Concurrently with the rat studies, comparable experiments were carried 

 out on adult monkeys, and they will be reported upon separately (neuro- 

 pathologic studies made in collaboration with Webb Haymaker, M.D., 

 Armed Forces Institute of Pathology, Washington, D.C.). These can be 

 briefly summarized. Five monkeys were irradiated by the same method and 

 exposures (3500 rads) were restricted to the same area of the vertebral 

 column as in the rats, i.e. to include the area from the sixth cervical to 

 second thoracic segment of the spinal cord. 



One monkey died from pneiniionia 3 months 3 days after irradiation 

 without showing neurologic signs, and no lesions were found in the irradi- 

 ated part of the spinal cord. One monkey developed neurologic signs 5 

 months 13 days after the irradiation; motor weakness of the lower limbs 

 started and progressed until there was complete paralysis without the legs 

 or tail being flaccid. There was also loss of sphincter control. In spite of 

 this, the monkey remained very agile and climbed around its cage and tree 

 by use of the arms alone. The animal was sacrificed for study of the nervous 

 system after a clinical course of 4 weeks. A malacic myelopathy similar to 

 that in experimental rats was found in the irradiated part of the spinal cord. 

 Two of the monkeys developed neurologic signs between 6 and 61/2 months 

 postirradiation. Another monkey developed signs 8 months 13 days after 

 irradiation, but the paralytic course was thereafter very acute and the animal 

 was killed when moribund, 4 days after the onset of clinical signs. 



Fig. 3. Another rat. Latent period 5yi months, duration of cHnical signs 2 days 

 before sacrifice. At this level, the lesion is more pronounced on one side of ventro- 

 lateral column than the other. Hematoxylin-eosin X 16. 



Fig. 4. High magnification from area in Fig. 1 marked by arrow. Pia mater and 

 nerve roots on right; gray matter, left. Almost complete tissue dissolution of white 

 matter witli no neuroglial response. Hematoxylin-eosin. X 100. 



