Effects of dorsal root entry zone lesions on CSF and plasma neuropeptides and catecholamines

Do low levels of beta-endorphin in the cerebrospinal fluid indicate defective top-down inhibition in patients with chronic neuropathic pain? A cross-sectional, comparative study

OBJECTIVE

Pain medicine still lacks mechanism-specific biomarkers to guide diagnosis and treatment, and defective top-down modulation is an important factor in the pathophysiology of chronic pain conditions. Using modern analytical tools and advanced multivariate statistical analysis, the aim of this study was to revisit two classical potential biomarkers of pro- and anti-nociception in humans (substance P and beta-endorphin), focusing particularly on the cerebrospinal fluid (CSF).

DESIGN

Cross-sectional, comparative, observational study.

SUBJECTS

Patients with chronic, post-traumatic and/or post-surgical, neuropathic pain refractory to conventional treatment (N = 15) and healthy controls (N = 19) were included.

METHODS

Samples were taken from CSF and blood, and levels of substance P and beta-endorphin were investigated using a Luminex technology kit.

RESULTS

We found low levels of beta-endorphin in the CSF of neuropathic pain patients (66 ± 11 pcg/mL) compared with healthy controls (115 ± 14 pcg/mL) (P = 0.017). Substance P levels in the CSF did not differ (20 ± 2 pcg/mL, 26 ± 2, P = 0.08). However, our multivariate data analysis showed that belonging to the patient group was associated with low levels of both substances in the CSF. A higher correlation between the levels of beta-endorphin and substance P in CSF was found in healthy controls than in patients (rs  = 0.725, P < 0.001 vs. rs  = 0.574, P = 0.032).

CONCLUSIONS

Patients with chronic neuropathic pain due to trauma or surgery had low levels of beta-endorphin in the CSF. We speculate that this could indicate a defective top-down modulation of pain in chronic neuropathic pain. Our results also illustrate the importance of taking a system-wide, multivariate approach when searching for biomarkers.

Treatment of Refractory Pain after Brachial Plexus Avulsion with Dorsal Root Entry Zone Lesions

OBJECTIVE

Significant numbers of patients experience intractable pain after brachial plexus root avulsions. Medications and surgical procedures such as amputation of the limb are often not successful in pain treatment.

METHODS

Forty-seven patients with intractable pain after traumatic cervical root avulsions were treated with dorsal root entry zone coagulation between 1980 and 1998. The dorsal root entry zone coagulation procedure was performed 4 months to 12 years after the trauma, and patients were monitored for up to 18 years (average follow-up period, 14 yr).

RESULTS

Immediately after surgery, 75% of patients experienced significant pain reduction; this value was reduced to 63% during long-term follow-up monitoring. Nine patients experienced major complications, including subdural hematomas (n = 2) and motor weakness of the lower limb (n = 7). Improved coagulation electrodes with thermistors that could produce smaller and more-accurate lesion sizes, which were introduced in 1989, significantly reduced the number of complications.

CONCLUSION

Central deafferentation pain that persists and becomes intractable among patients with traumatic cervical root avulsions has been difficult to treat in the past. Long-term follow-up monitoring of patients who underwent the dorsal root entry zone coagulation procedure in the cervical cord indicated that long-lasting satisfactory relief is possible for the majority of individuals, with acceptable morbidity rates.