[Characterization of sensation disorders and neuropathic pain related to syringomyelia. A prospective study]

The present prospective study aimed to perform quantitative sensory testing (QST) in patients with painful or painless syringomyelia before and after surgical treatment of their syrinx (at 3 and 9 months). Eighteen consecutive patients with cervical or dorso-lumbar syringomyelia completed the study and 9 underwent surgery. Twelve patients had central neuropathic pain (of whom 6 were followed up). Spontaneous pain and brush-evoked allodynia were assessed. Von Frey hairs, vibrameter and a thermotest device were used to determine the mechanical-, vibratory-, thermal-detection thresholds, and the mechanical and thermal pain thresholds. Results showed evidence of deficits in temperature and pain sensibility in 17 cases, often associated with deficits in vibration and touch sensitivity (11 cases). Magnetic resonance scan, including axial images, demonstrated good correlation between paramedian extension of the syrinx and the laterality of thermal deficits. Somatosensory evoked potentials (11 patients) were abnormal in 9 cases at level, and showed good correlation with deficits in vibration. The magnitude of the thermal and tactile deficit was similar between areas of spontaneous pain and adjacent non painful areas. Surgery induced a significant decrease of tactile deficits, and to a lesser extent, of thermal deficits. Effects on neuropathic pain were positive in 3 patients (total disappearance of pain) and negligible or negative in 3 patients, despite collapse of the syrinx (in 2 cases). These results confirm that QST are useful in clinical practice to quantify the clinical results of surgery in patients with syringomyelia, and allow some hypotheses about the mechanisms of neuropathic pain in these patients.