The pain of postherpetic neuralgia is characterized as burning and lancinating and can persist for years after resolution of the acute infection. Allodynia (pain from non-noxious stimuli) is a frequent component of this condition. Methods of treating postherpetic neuralgia include opioid analgesics, antidepressants and anticonvulsants, but none of these therapies is consistently effective. Postmortem studies of patients who had prolonged postherpetic neuralgia have found a marked degree of spinal inflammation, suggesting a significant inflammatory component to this condition. Kotani and colleagues performed a randomized, controlled trial to assess the benefit of intrathecal methylprednisolone as a treatment for postherpetic neuralgia.
Eligible patients had intractable postherpetic neuralgia persisting for at least one year after the healing of all vesicular lesions. The pain had to be restricted to the original dermatomes of the zoster rash. Excluded were patients who were immunocompromised, had pain in the trigeminal nerve region and had previously responded to conventional therapies such as topical analgesics, antide-pressants or anticonvulsants.
All patients underwent treatment with other standard oral or topical modalities for four to six weeks if they had not previously been tried. Patients were then treated with the nonsteroidal medication diclofenac for four weeks. Next, patients were randomized to receive intrathecally injected doses of 3 mL of 3 percent lidocaine alone or in combination with 60 mg of methylprednisolone at the L2-L3 intervertebral disc space for four weeks. A third control group received only diclofenac and did not undergo lumbar puncture. Patients in the first two groups were allowed to continue diclofenac therapy as needed.
Pain was evaluated in all patients before randomization, at the end of the treatment period and at one month, one year and two years post-treatment. The severity of lancinating pain, burning pain and allodynia were quantified with a 10-cm visual analog scale. Global pain relief was assessed by a similar scale and classified as excellent (greater than 75 percent relief), good (50 to 75 percent relief), fair (25 to 49 percent relief) or poor (less than 25 percent relief). Levels of interleukin-8 (IL-8) in the spinal fluid were measured before and after treatment. IL-8 is a known marker of inflammation.
A total of 270 patients were included in the study and randomized to three groups. The mean age was 64 years, with an equal distribution of men and women. The mean duration of neuralgia was more than 38 months. Approximately 90 percent of patients in the methylprednisolone-lidocaine group had excellent or good global pain relief at all follow-up visits. Fifteen percent of patients in the lidocaine group had initial improvement that was excellent or good, but more than one half had recurrent pain at the follow-up visits. Fewer than five percent of the control group reported a similar level of relief at any of the follow-up visits. Patients receiving methylprednisolone-lidocaine reported a greater than 70 percent reduction in severity of all three types of pain compared with less than 25 percent reduction in the patients receiving only lidocaine. The use of diclofenac decreased by more than 70 percent in patients receiving methylprednisolone-lidocaine, by less than 20 percent in patients receiving lidocaine and not at all among patients in the control group during the four weeks after treatment. Cerebro-spinal fluid levels of IL-8 decreased significantly in patients in the methylprednisolone-lidocaine group but did not change in the other two groups. The decrease in IL-8 had a direct correlation with the duration of neuralgia before treatment and global pain relief.
The authors conclude that intrathecal administration of methylprednisolone produces good to excellent pain relief in patients with refractory postherpetic neuralgia. In addition, the pain relief lasts for at least two years, and the therapy does not produce any adverse effects.