Electrophysiologic evidence of subclinical injury to the posterior columns of the human spinal cord after therapeutic radiation

Abstract

Spinal somatosensory conduction velocity (SSCV) was indirectly estimated from cerebral evoked potentials in 15 adults who had received therapeutic radiation (RT) (2000-4380 rad) to the thoracic spinal cord during treatment for lung cancer, and in 15 age-matched normal controls. Thirteen of the patients had also received 4400-5500 rad to the supraclavicular fossae. One-way impulse conduction time in the arm, estimated from F-wave latency, was prolonged in the patients as compared to controls (12.0 +/- 1.2 versus 10.4 +/- 1.0 msec; P less than 0.001) but conduction time in the leg was similar in the two groups (22.4 +/- 2.4 versus 22.0 +/- 2.5 msec; P less than 0.1). SSCV was significantly slower in the patient group (37.9 +/- 13.9 versus 54.5 +/- 12.9 m/sec; P less than 0.001) whereas supraspinal latency (cervical cord to cortex) was identical (5.5 +/- 0.9 versus 5.5 +/- 0.8 msec; P less than 0.1). SSCV in the patient group was not related to total RT dose (r = 0.15; P = 0.2), but was correlated with both treatment time and number of fractions (r = 0.49 and 0.43; P = 0.003 and 0.007, respectively). These findings suggest that RT may produce subclinical spinal cord dysfunction even at conventional dosage schedules, and that it may be possible physiologically to monitor the myelopathic effects of RT in individual patients.