Coping With Postherpetic Neuralgia

THE CASE:A 79-year-old woman with a 37-year history of type 2 diabetes mellitus complains of head pain that began more thana month ago and is localized to the left frontotemporal region. She characterizes the pain as constant and burning, with minimalfluctuations in intensity. The pain does not increase with any particular activity but is quite disabling; it has causedemotional lability and insomnia. She denies nausea, visual disturbances, weakness of the extremities, dizziness, or tinnitus.Her appetite is depressed; she has experienced some weight loss.

The patient has no history of headache or head injury. On detailed questioning, she recalls that about 2 monthsearlier, she experienced a rash and pain above the left eye that lasted for 3 weeks.

THE DIALOGUE:Headache specialist: If your patient's rash was unilateral,vesicular or bulbous, and later pustular, and followed thetrigeminal dermatome distribution, I would suspect postherpeticneuralgia (PHN). Intense, burning head pain thatis associated with an elevated erythrocyte sedimentationrate--but not a history of skin lesions--may indicate temporalarteritis.

Primary care doctor: The rash above the patient's eye startedas vesicles, progressed to the pustular stage in about aweek, and later formed a crust. What is the likelihood thatPHN will develop in a patient with varicella-zoster virusinfection?

Headache specialist: More than 1 million new cases of herpeszoster occur each year. The annual incidence of herpeszoster in persons younger than 20 years is about 1 per1000, but after age 80 years, it increases 5- to 10-fold.

The most common clinical presentations of herpeszoster are:

• Pain that precedes the eruption of the rash by severaldays or weeks.
• Pain that accompanies or follows the appearance of therash for up to 4 weeks.

PHN develops in approximately 10% to 35% of affectedpatients. Prompt treatment reduces the incidence ofchronic postherpetic pain by 50%. Lack of treatment resultsin a 70% likelihood of persistent pain. An estimatedone half of patients with herpes zoster who are older than70 years report PHN that persists for more than 1 year.¹

Doctor: How does the pain of herpes zoster differ fromthat of PHN?

Headache specialist:

Acute herpes zoster usually causessharp, stabbing, throbbing, shooting, and hot pain.Generally, 3 different types of pain are associatedwith PHN:

• Burning or steady and throbbing.
• Shooting or intermittent and sharp.
• Allodynia (pain produced by normally non-noxiousstimuli).

Many patients with prolonged PHN also experiencesleep difficulties, depression, anxiety, and diminishedappetite, sexual drive, and energy. Those symptoms maybe as disabling as the pain.

Doctor: How typical is allodynia?

Headache specialist: It occurs in 90% of patients with PHN.These patients also experience loss of tactile and thermalsensation. Allodynia is triggered by very light strokingof the skin and can be blocked or alleviated by firm pressure.Patients who have acute herpes zoster without PHNalmost never exhibit allodynia.

Doctor: At what point does the pain of acute herpes zosterevolve into PHN?

Headache specialist: Acute herpetic neuralgia precedes oraccompanies the eruption of a rash; it may persist forup to 30 days. Subacute herpetic neuralgia persists afterthe skin eruption has healed but resolves within 4 monthsof onset of the original infection. PHN persists beyond4 months from the initial onset of the rash.²

Doctor: What are the risk factors for PHN?

Headache specialist:

They include advanced age, immunocompromisedstatus, and stress. Data from numerousstudies have also shown that the following factors duringthe acute phase of herpes zoster greatly increase therisk of prolonged PHN:

• Pain severity.
• More significant cutaneous manifestations, includingscarring.
• Greater sensory dysfunction in the affected dermatome.

Other risk factors include a painful prodrome, temperaturehigher than 38^oC (100.4^oF), and greater extentand duration of the humoral and cell-mediated immuneresponse during acute herpes zoster.¹

Doctor: Herpes zoster and PHN can be very difficult tomanage. What are your recommendations?Headache specialist: The goal for treatment of patientswith acute herpes zoster is pain control and preventionof PHN. Start therapy immediately following the onsetof symptoms. Begin antiviral therapy within 72 hours,along with a tricyclic antidepressant (for neuropathicpain), analgesics, and a short course of systemic corticosteroids.Antiviral agents, such as acyclovir, famciclovir,and valacyclovir, can reduce the intensity and durationof pain of acute herpes zoster, accelerate the healing ofskin lesions, and prevent scarring. However, there is noevidence that antiviral therapy can prevent PHN.³Opioids--preferably long-acting formulations--canalso be used to control pain if necessary. However, thenausea, vomiting, and constipation that these agents causein some patients--especially elderly ones--may rule themout.

Doctor: What are your suggestions for optimal managementof PHN?

Headache specialist: Continue the tricyclic antidepressantfor at least 6 weeks after the onset of symptoms. To ensurethat the pain does not recur, have the patient continuea low-dose antidepressant for 6 additional weeks. Ifsymptoms persist beyond 4 to 6 weeks from the onset ofthe rash, increase the dose. Anticholinergic and sedativeside effects of tricyclic antidepressants can be difficult tomanage in elderly patients. In placebo-controlled studies,selective serotonin reuptake inhibitors and other antidepressantshave failed to reduce pain.

Opioids are marginally effective in controlling neuropathicpain, pain that persists through subacute herpeticneuralgia, and PHN. Clonidine may provide modest painrelief by inhibiting the release of nocigenic transmitters.Topical analgesic agents, such as capsaicin (hot pepperextract), applied to unbroken skin produce moderaterelief by depletion of substance P. A 5% lidocaine patchoften controls pain and allodynia. Sympathetic nerveblockade or epidural analgesia is effective in some patients.More complicated neurosurgical interventions,such as electrical stimulation of the thalamus or spinalprocedures, are risky, and their success has been reportedonly anecdotally.

Add an anticonvulsant, such as carbamazepine, oxcarbazepine,topiramate, or gabapentin, to control PHN. Themechanism of action is not fully understood, but neuronalsodium or calcium channels may play a role in chronic neuropathicpain. Gabapentin has also been shown to improvesleep, mood, and quality of life.⁴

Because PHN is often chronic and debilitating, patientsmay experience emotional distress. Supportive psychotherapyis warranted for those affected.

References:

REFERENCES:

1.

Drown RH, Portenoy RK. Pain and its persistence in herpes zoster. Pain.1996;67:241-251.

2.

Bajwa ZH, Ho CC. Herpetic neuralgia: use of combination therapy for painrelief in acute and chronic herpes zoster. Geriatrics. 2001;56:18-24.

3.

Wood MJ, Johnson RW, McKendrick MW, et al. A randomized trial of acyclovirfor 7 days or 21 days with and without prednisolone for treatment of acuteherpes zoster. N Engl J Med. 1994;330:896-900.

4.

Rowbotham MC, Harden N, Stacey B, et al. Gabapentin for the treatment ofpostherpetic neuralgia: a randomized controlled trial. JAMA. 1998;280:1837-1842.