Light and electron microscopic alterations in spinal cord myelin sheaths after decompression sickness.

Pathological examination of spinal cords from animals subjected to experimental decompression sickness (DCS) was undertaken in an attempt to explain the disparate response to treatment observed. Eight experimental animals, four undived control animals, and two dived but untreated animals were perfusion fixed, and the spinal cords were removed. Light microscopy of toluidine blue stained, ultrathin sections from dived animals demonstrated a distinctive widened myelin sheath showing a banded pattern of myelin disruption. This pattern was confirmed by electron microscopy and showed the separation to be between abutting double layers of myelin. Artifactual changes were also present in dived and undived animals. These previously unreported changes may be caused by DCS. They are compatible with the major mechanisms proposed in the pathophysiology of spinal cord DCS and may also account for the response to treatment seen in our experimental animals. It is suggested that these findings may also explain the response to treatment seen in patients, together with the formation of late lesions described in the spinal cords of long-term survivors of DCS.