We believe that by decreasing the PEG concentration using our method, MPA-related complications will potentially be reduced, and this should be considered in patients with postherpetic neuralgia refractory to other treatments who might be candidates for repeated intrathecal injections.
Postherpetic neuralgia (PHN) is the most common complication of herpes zoster. Patients older than 60 years of age have a higher risk of PHN than do the younger patients. 1,2 There are many definitions of PHN in the literature in terms of timing (following rash healing, versus a defined time after onset of herpes zoster, 1 or 2 mo), duration (any time after zoster or a minimum of 6 mo after zoster), and type of pain (such as lancinating pain or allodynia). 3 PHN may include a wide array of presentations, from brief intermittent mild pain that resolves spontaneously to chronic recalcitrant, persistent, and severe pain unremitting to multiple therapies. A prospective study conducted on 457 patients with herpes zoster suggests that a physician can expect to see 4 cases of herpes zoster per year and 1 case of PHN lasting more than 3 months every 3 years. 4 Meta-analysis of 42 randomized controlled trials of acute zoster treatments have shown the incidence of pain at 3 months to be between 17 and 60%. 5 There is limited evidence that any of the conventional therapies for treating acute zoster have an impact on development of PHN. 5,6
Injection directly into the neural tissue of a brachial plexus root in a cadaver model produced high pressures suggestive of intrafascicular injection and widespread flow of the injectate through the distal brachial plexus. However, proximal movement of the dye-containing injectate was more restricted, with only 1 of the injections leading to epidural spread and no apparent effects on the spinal cord.
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