Induced lumbosacral radicular symptom referral patterns: a descriptive study

Abstract Background Context Lumbosacral radicular symptoms are commonly evaluated in clinical practice. Level-specific diagnosis is crucial for management. Clinical decisions are often made by correlating a patient's symptom distribution and imaging with sensory dermatomal maps. It is common for patients to describe non-dermatomal symptom patterns and for imaging to demonstrate pathology at levels not predicted by a dermatomal map. These observations suggest that the referred symptom distribution from lumbosacral nerve root provocation is different from dermatomal maps. This phenomenon has been demonstrated in the cervical spine but not in the lumbosacral spine. Purpose The objective of this study was to characterize potential lumbosacral radicular symptom referral patterns induced during transforaminal epidural injections. Study Design/Setting This is an observational descriptive study. Patient Sample The patient sample included 71 consecutive patients with lumbosacral radicular pain undergoing lumbosacral transforaminal epidural injections at an outpatient interventional spine practice. Outcome Measures Each subject drew the location of provoked lumbosacral radicular symptoms on a pain diagram. Materials and Methods Seventy-one consecutive patients undergoing 125 fluoroscopically guided lumbosacral transforaminal epidural injections at an outpatient interventional spine practice were included in the study. The described location of provoked symptoms was recorded (1) after final needle positioning, (2) after injection of up to 0.5 mL of contrast solution, and (3) after injection of up to a 1 mL test dose of 1% lidocaine. Each subject drew the location of provoked symptoms on a diagram. The provoked symptom diagrams for each lumbosacral segmental level were combined to create composite nerve root, level-specific, symptom referral pattern maps. Results Of the 125 injections, 87 provoked referred symptoms and were included in the analysis. Thirty-eight injections did not provoke referred pain symptoms and were excluded from further analysis. Four nerve roots were tested at L1 and eight were tested at L2. Because of the small number of subjects, composite diagrams and statistical analysis were not completed for these levels. Eleven nerve roots were analyzed at L3, 28 at L4, 34 at L5, and 11 at S1. Composite symptom referral pattern maps were created for levels L3, L4, L5, and S1. Although the symptom distribution occasionally followed the expected dermatomal maps, most often the referral was outside of the patterns expected for each level. The most common symptom referral pattern for levels L3–S1 was the buttock, the posterior thigh, and the posterior calf. Conclusions The level-specific provoked symptom distribution during lumbosacral transforaminal epidural injections is frequently different from that predicted by classic lumbosacral dermatomal maps. Referred pain to the buttock, the posterior thigh, or the posterior calf may come from L3, L4, L5, or S1 nerve root segmental irritation.