75 Postherpetic Neuralgia

Case 75 Postherpetic Neuralgia

Isaac Chan and Christopher J. Winfree

Clinical Presentation

A 70-year-old woman on chronic prednisone therapy for polymyositis presents 5 months previously with an outbreak of herpes zoster infection along her left abdomen and groin in a T12–L1 distribution.
She experiences severe, intractable pain radiating “like a knife” within the distribution of the zoster rash.
Although the rash gradually resolves, the pain persists, unchanged to the present.
The pain grades an 8/10 in severity, is ameliorated partially with cold packs, and is worsened with movement.

Questions

What is this patient’s diagnosis?
What are her treatment options in the acute period (within 72 hours of rash onset)?
What are her treatment options in the chronic period (after the rash is resolved)?
What invasive treatment options are available if more conservative measures fail?
The patient undergoes a variety of pharmacologic treatments, including topical creams, oral anticonvulsants, antidepressants, and opiates, none of which yielded acceptable pain relief. Multiple epidural steroid injections likewise failed to help. You are considering offering the patient either neurostimulation or a spinal infusion pump.
Describe the relative merits and drawbacks of each type of therapy.

Answers

What is this patient’s diagnosis?

Initially, this patient had an acute herpes zoster outbreak, in which a dermatomal outbreak of pain is followed by a vesicular rash that gradually resolves over a month or so.1

Zoster pain that persists well beyond healing of the rash is called postherpetic neuralgia (PHN), and occurs following 10 to 15% of acute zoster infections.¹
What are her treatment options in the acute period (within 72 hours of rash onset)?
- Topical analgesics and oral anticonvulsants and antidepressants offer pain relief, but do not reduce the likelihood of developing PHN.
- Oral antiviral agents administered within 72 hours of the onset of the acute outbreak may reduce the likelihood of developing PHN.²
What are her treatment options in the chronic period (after the rash is resolved)?
- Randomized, prospective clinical trials have shown that oral antidepressants, anticonvulsants, long-acting opioids, and nonsteroidal antiinflammatory agents as well as topical anesthetic creams reduce pain in patients with PHN.¹
- Complementary and alternative medicine therapies such as physiotherapy and acupuncture have not been shown to be beneficial but may certainly be utilized with essentially no risk to the patient.
What invasive treatment options are available if more conservative measures fail?
- Minimally invasive pain management techniques such as nerve blocks, sympathetic blocks, and epidural steroids have not been shown to be of benefit.¹
- Invasive surgical options such as neurectomy, cordotomy, dorsal root entry zone lesions, or other ablative therapies have been discredited and largely abandoned because of their risk of complications and lack of efficacy.3
- Less-invasive treatments such as intrathecal methylprednisolone infusion may be helpful.⁴
- Spinal cord stimulation, in which implanted electrodes in the spinal canal administer electrical impulses to the dorsal columns, may reduce pain and improve quality of life in PHN patients.⁵
Describe the relative merits and drawbacks of each type of therapy.
- Spinal infusion pumps may offer dramatic pain relief for patients with chronic pain, including PHN. Implanting the devices is fairly straightforward for the practicing pain physician, and patients generally tolerate the systems fairly well. Patients generally do not perceive the effects of the infused drug(s), except for the relief of the pain.⁶
- Nevertheless, the pumps need to be refilled every 1 to 3 months or so, and replaced every 5 to 7 years. System malfunctions may occur, prompting potentially lethal withdrawal syndromes in certain cases, and surgical revisions are sometimes required. Cerebrospinal fluid (CSF) leaks sometimes occur, following pump implantation or revision surgery.
- In contrast, spinal cord stimulation systems generally require less maintenance than infusion pumps, there is no risk of a withdrawal syndrome if the system malfunctions, and CSF leaks are rare.
- Stimulation produces noticeable paresthesias that are designed to overlap with the painful areas, eliciting pain relief. Some patients find these sensations annoying, especially if the paresthesias are in unwanted areas outside of the pain distribution.⁷
- Spinal nerve root stimulation is a neurostimulation technique similar to spinal cord stimulation, except that the electrodes are placed more laterally in the spinal canal to preferentially stimulate the dorsal rootlets (Fig. 75.1). This provides similar levels of pain relief within the targeted painful areas as spinal cord stimulation, while limiting unwanted stimulation paresthesias to undesired areas.⁸
- Possible complications or drawbacks of neurostimulation implants include electrode displacement or malfunction, hematoma or pain at the site of pulse generator, requirement for battery replacement after 5 to 10 years.⁷