THE FUNCTION OF SENSORY NERVE-FIBERS IN LUMBAR RADICULOPATHY - USE OFQUANTITATIVE SENSORY TESTING IN THE EXPLORATION OF DIFFERENT POPULATIONS OF NERVE-FIBERS AND DERMATOMES

Study Design. The function of sensory nerve fibers in patients with lu mbar radiculopathy and in control individuals was evaluated using quan titative sensory testing. Objectives. To investigate the effect of lum bar nerve root compression on different populations of nerve fibers an d to explore the function of sensory nerve fibers in neighboring nerve roots not involved in the mechanical compression.Background Data. Res ults from experimental and clinical studies indicate that chronic comp ression of lumbar nerve roots affects the large myelinated nerve fiber s. The majority of nerve fibers involved in the sensation of pain, how ever, are small afferent nerve fibers. It is therefore of interest to study the effect of compression on large and small sensory afferent ch annels. Several authors have elucidated the biochemical interaction be tween disc tissue and nerve roots. Chemical substances in the epidural space can reach the nerve fibers in nerve roots at the same or neighb oring lumbar segments. In this way, fibers not involved in the mechani cal compression may be affected. Methods. The small nerve fibers were studied using tests for thermal thresholds (thermotest), and the large myelinated fibers were studied by vibrametry. Forty-two patients were investigated in the symptomatic and the asymptomatic leg, and the res ults were compared with those of 21 healthy individuals. Results. The thresholds of cold, warmth, and vibration were significantly increased in the dermatome of the compressed nerve root, indicating that large and small sensory nerve fibers were affected. Further, the thresholds were significantly increased in the neighboring dermatomes in the symp tomatic and the asymptomatic leg. Conclusion. Large and small sensory afferent nerve fibers are affected in lumbar radiculopathy. The increa se in sensation thresholds in the ipsilateral neighboring dermatome an d in the dermatomes in the asymptomatic leg indicates that adjacent ne rve roots are involved in the pathophysiology of sciatica in patients with lumbar disc herniation.