Post herpetic neuralgia (PHN)

Anil Abraham

 Dept. of Dermatology, St. John's Medical College Hospital, Bangalore-560 034, India

Correspondence Address:
Anil Abraham
Dept. of Dermatology, St. John's Medical College Hospital, Bangalore-560 034
India

Dermatologists have to manage post herpetic neuralgia (PHN) because their patients expect them to deal with the pain after zoster and not only to treat the vesicular rash. It is ideal to manage the case if possible, without always referring to a neurologist.

I observe carefully any pain persisting after herpes zoster has healed and use the term post herpetic neuralgia when pain persists for more than 3 months after the rash heals.

There are 3 classical of PHN: constant burning pain (Amitryptiline group are the drugs of choice) intermittent stabbing pain (carbamazepine group are drugs of choice), and the combination/Allodynia type.

The risk factors for developing neuralgia are older age (infrequent < 40 years age), greater acute pain severity, greater rash severity, sensory dysfunction in dermatome during zoster, painful prodrome pre-ceding and others including trigeminal distribution, psychosocial stress or fever. In patients with high risk and no other contraindication a short course of steroids during acute zoster helps to prevent PHN.

I manage severe cases of PHN in the following manner.

A. General measures

The patient is asked to use loose cotton clothes especiallly for thoracic or lumbosacral zoster. A layer of Duoderm R or Cling film (used in the refrigerator to cover dishes) can be used as a protective separation between the skin and clothes. In severe cases cold compresses with an ice pack or a packet of frozen meat or vegetables from the freezer helps. Reassurance and explanation regarding the nature of disease are a vital part of treatment, as is psy-chotherapy.

B. Topical treatment

Capsaicin invariably leads to a burning sensation and poor patient compliance. I have found EMLA under occlusion useful topically and look forward to the Lidoderm patch or gel (which is US FDA approved) becoming available locally. Another good advance in severe cases is the Fentanyl transdermal patch (Brand name DUROGESIC (25, 50 and 100 micrograms) Johnson & Johnson 25mcgr per hour sells for Rs. 1,150/- per patch. One patch lasts for only 72 hours. It is very useful in severe cases.

C. Oral Medications

1. Antidepressants (tricyclic)Though amitryptiline is the most widely used it has the side effects of sedation, anticholinergic action and postural hypotension which make it un-suitable for elderly patients. Nortryptiline is better tolerated (Sensival 25mg) and is a better choice. I start with 25mg at bedtime and build up by 25mg weekly to a maximum of 150mg/day or pain relief whichever is earlier.

2. AnticonvulsantsCarbamazepine or phenytoin is traditionally used, but adverse effects once again make patients non-compliant. Gabapentin is a better drug with excel-lent tolerability, improvement in pain ratings, sleep, mood and quality of life. It should be considered the first line treatment in those without depression. It is available as Gabantin, and is started at 100-300mg 3 times daily and built up at 300mg increments to a maximum of 3600mg/day or pain relief whichever is earlier.