Efficacy of intrathecal midazolam with or without epidural methylprednisolone for management of post-herpetic neuralgia involving lumbosacral dermatomes.

BACKGROUND Post herpetic neuralgia is a chronic neuropathic pain syndrome which remains one of the most difficult pain disorders to treat. Epidural injection of methylprednisolone with or without local anesthetic provides relief for neuralgia for a short duration only. Recent studies have shown a promising anti nociceptive effect for intrathecal midazolam, a water soluble benzodiazepine, due to its interaction with benzodiazepine-GABA-A receptor complex within the spinal cord. STUDY DESIGN A randomized, double blind study was conducted at 2 different centers in India. SETTING Two different interventional pain practice centers in India. OBJECTIVES To quantify the effectiveness of a single intrathecal injection of midazolam 2 mg with and without epidural methylprednisolone 60 mg for management of pain and allodynia in 150 adult patients with postherpetic neuralgia of 3-6 months duration involving lumbosacral dermatomes. METHODS Patients in Group M-0 (n=50) received epidural methylprednisolone (60 mg), patients in group M-1 (n=50) received midazolam 2 mg in the intrathecal space while patients in Group M-2 (n=50) received methylprednisolone (60 mg) in the epidural space plus midazolam 2 mg in the intrathecal space. RESULTS The administration of intrathecal midazolam (2 mg) provided short term improvement in post herpetic neuralgia similar to epidural methylprednisolone. However, the combination of intrathecal midazolam with epidural methylprednisolone resulted in prolonged duration of analgesia in patients with post herpetic neuralgia. The need for analgesics was also significantly less in patients who received the combination compared to those who received either intrathecal midazolam or epidural methylprednisolone. No serious adverse effect was reported with the use of intrathecal midazolam except a mild degree of sedation. CONCLUSION The combination of intrathecal midazolam with epidural methylprednisolone resulted in prolonged duration of analgesia in patients with post herpetic neuralgia of lumbosacral dermatomes due to the complementary anti nociceptive action of intrathecal midazolam with epidural methylprednisolone on spinal nerve roots. LIMITATIONS The dose-response relationship of intrathecal midazolam was not evaluated in our study, so further study should be conducted with different doses of intrathecal midazolam for management of PHN.