Misdiagnosis of symptomatic lumbar lateral stenosis (LS) may result in an unfavourable prognosis after surgical treatment. This study investigated the diagnostic accuracy of a standardised qualitative sensory test (SQST) in the detection of symptomatic LS in patients who had degenerative spinal disorders involving the L5 spinal nerve. We prospectively identified 75 patients, of which 60 met the inclusion criteria. Lateral recess stenosis at the L5 level or foraminal stenosis at the L5/S1 level on MRI was identified and graded by a neurosurgeon blinded to any clinical information. The reference criteria for the diagnosis of symptomatic LS were grade III LS on MRI and relevant clinical symptoms. Cutaneous sensory functions of the L5 dermatome on the symptomatic side were evaluated using the SQST. Each item of the SQST showed a satisfactory performance in the diagnosis of LS (sensitivity = 0.455-0.727, specificity = 0.868-1.0). A stepwise selection model identified low-strength von-Frey, high-strength von-Frey, and vibration as the most accurate predictors of symptomatic LS with an area under the receiver operating characteristic curve of 0.9563 (95% confidence interval = 0.9003-1.0). In combination with MRI, the SQST is a promising diagnostic tool for detecting symptomatic LS involving L5 nerve roots.
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