Clinical and electrophysiologic characteristics of compressed lumbar nerve roots.

STUDY DESIGN: Clinical and electrophysiologic data of compressed nerve roots were evaluated in patients with lumbar disc herniation.

OBJECTIVES: To elucidate the characteristics of the nerve root with respect to preoperative neural deficit and to analyze the predictive factors for recovery of leg paralysis after posterior discectomy.

SUMMARY OF BACKGROUND DATA: Prolonged paralysis due to disc herniation is reported to be a poor prognostic factor for motor recovery. In addition, an intraoperative somatosensory evoked potential change has been reported to be correlated with clinical outcome.

METHODS: Among 64 patients with a lumbar disc herniation, a variety of clinical data, such as age, gender, duration of leg paralysis or leg pain, the angle of the positive straight leg raising test, and time for recovery from paralysis, were investigated. In addition, threshold, amplitude of compound muscle action potentials, and latency for 85 nerve roots were monitored before and after discectomy. Data were analyzed according to the grade of preoperative neural deficits: Grade 1, severe motor and sensory loss; Grade 2, mild motor and sensory loss; Grade 3, sensory loss only; Grade 4, no deficit (leg pain only); and Grade 5, asymptomatic control.

RESULTS: The nerve root threshold before discectomy showed an increase in accordance with the severity of neural deficit. Thresholds of Grade 1 and 2 nerve roots were significantly higher than those of normal control subjects. The average amplitudes of compound muscle action potentials before discectomy in Grade 1 and 2 nerve roots were significantly lower than those of asymptomatic control nerve roots. Elongation of latency also showed a correlation with preoperative neurologic abnormality. Patients who complained of leg pain only were significantly younger, and those who showed severe motor disturbance tended to be older and to show a straight leg raising test angle similar to that of control nerve roots. Severe motor weakness for more than 6 months, a negative straight leg raising test, and age were considered to be poor prognostic factors for motor recovery.

CONCLUSIONS: Findings of increased threshold, low amplitude of compound muscle action potentials, and elongated latency correlated with degree of motor weakness. Early decompression for compressed nerve root is recommended, especially in older patients with severe motor weakness presenting a negative straight leg raising test.