Electrodiagnostic characteristics of upper lumbar stenosis: Discrepancy between neurological and structural levels

Abstract

Conventional knowledge suggests that n/n + 1 level lesion will result in n + 1 radiculopathy in the lumbar spine. However, anecdotal reports on spinal stenosis at upper lumbar levels suggest a difference. This study aimed to investigate electrodiagnostic manifestation of upper lumbar stenosis. Consecutive patients were recruited from a university hospital. Inclusion criteria were spinal canal stenosis at L1/2, L2/3, or L3/4 level confirmed in magnetic resonance image (MRI), abnormal electromyography (EMG) including active denervation potentials, and MRI and EMG conducted within 3 months interval. Exclusion criteria were concomitant peripheral polyneuropathy of clinical significance, structural lesions at L4/5 or L5/S1 levels in MRI to explain EMG abnormalities. 24 patients were included and 10 patients were excluded; 14 patients were enrolled in the study. All the patients showed denervation potentials in the distal lower extremity muscles innervated by L5 and S1 roots although the structural lesions were above. L2, L3, or L4 myotomes were rarely affected; only one case exhibited chronic reinnervation in the vastus medialis. Active denervation in the proximal L5 or S1 innervated muscles were observed in 8 patients. Any neuropathic findings were observed bilaterally in 10 patients. All the EMG findings could be categorized into 4 types based on symmetry, length-dependency, and myotomal distributions: symmetric, length-dependent (5), bilateral, asymmetric, non-length-dependent (5), unilateral, non-length-dependent (2), and mono-radiculopathy (2). In conclusion, general belief on lumbar radiculopathy was not applicable to upper lumbar stenosis. Without the knowledge of electrodiagnostic characteristic of upper lumbar stenosis, it might be confused as a peripheral polyneuropathy or polyradiculitis.