WARM AND COLD SENSORY THRESHOLDS IN PATIENTS WITH UNILATERAL SCIATICA- C-FIBER ARE MORE SEVERELY AFFECTED THAN A-DELTA FIBERS

Objectives - In order to evaluate if nerve root compression or inflamm ation is the most important pathogenetic mechanism in lumbar radicular pain, we investigated unmyelinated C-fiber function (warm sensation) and myelinated A-delta fiber function (cold sensation) in patients wit h unilateral L-5 or S-1 sciatica. Material and methods - Forty consecu tive patients with clinical and radiological evidence of unilateral L- 5 (n=29) or S-1 (n=11) sciatica were studied. The warm and cold sensor y thresholds (Somedic thermotest, method of limits) were measured on t he anterolateral leg (L-5 dermatome) and on the calf (S-1 dermatome) o n both sides. Results - Warm thresholds were significantly higher on t he symptomatic side compared to the non-symptomatic side (8.4+/-3.0 vs 6.2+/-2.5 degrees C, P<0.0005) in the affected dermatome. In a subgro up with confirmed disk herniation at surgery (32 of the 34 operated), significant differences between the symptomatic and the non-symptomati c side for the affected dermatome, were found for both warm (P<0.0005) and cold (P=0.003) thresholds. No threshold difference was seen in pa tients with disk herniations contained within the outer annulus fibros is (n=22) compared to those with non-contained herniations (n=10). Con clusions - Patients with unilateral sciatica and L-5 or S-1 nerve root involvement had increased warm thresholds suggesting impaired C-fiber function. Cold thresholds were significantly elevated in a subgroup w ith operatively confirmed disk herniation. Because myelinated axons ar e affected more by compression than unmyelinated ones, our results sug gest that nerve root inflammation is more important than compression p er se in the generation of sciatic pain.