An estimated 6.9% to 10% of the population is believed to suffer from neuropathic pain,1 the result of damage to nerves, the spinal cord, or the brain.
A wide variety of painful conditions fall under the heading of neuropathic pain including central pain conditions, where there is damage to the central nervous system, such as post-stroke pain and pain secondary to Parkinson's Disease; conditions where the pain appears to result from both some form of peripheral injury and a central nervous system response to this, eg, complex regional pain syndrome; and those where the damage is believed to be in peripheral nerves.
In the category of neuropathic pain caused by damage to peripheral nerves are the two most common forms: postherpetic neuralgia and diabetic peripheral neuropathic pain. This primary care update will focus on these although for the most part the treatment approaches that are effective for the these conditions are also appropriate for most of the other forms of neuropathic pain.
Postherpetic Neuralgia (PHN)
PHN results from a reactivation of the varicella zoster virus in persons who have had varicella. Reactivation is generally a result of age-related decline in immunity but may also be related to immune compromise caused by other disease or by drugs.
With the development of a varicella vaccine, the risk of contracting the virus has been greatly reduced. For those who have had chickenpox, vaccination can help prevent PHN.
The bad news is that many people in the age group most at risk for PHN (age ≥ 50 years) still haven't received the vaccine; also, the vaccine does not provide 100% immunity and the protection it does provide appears to decrease over time, leaving even those who receive it vulnerable to PHN.
PHN primarily affects those over age 50. In the US, PHN develops in approximately 18% of people age 50 or older and in 33% of those 80 or older.2 Diagnosis is typically straightforward as the pain is usually preceded by the herpes zoster rash along the distribution of a single nerve root and the pain follows the same distribution. By far the most common site of PHN is the thoracic region (Figure, above) followed by the face, along the distribution of the trigeminal nerve (Figure, below).
Pain from PHN is usually described as burning or lancinating. Allodynia over the affected area also is common—where stimulation that does not usually cause pain becomes painful. Even clothing rubbing lightly against the affected area can be painful. Allodynia is an uncommon symptom in most pain disorders and is typically only seen in one other neuropathic condition, complex regional pain syndrome (see box for discussion of this disorder).
If the patient seeks medical treatment for the herpes zoster rash within 72 hours after it develops, an antiviral medication (acyclovir, famcilovir, valacyclovir) may limit the severity.
Once the pain begins, an OTC analgesic (eg, acetaminophen or NSAID) may be sufficient. However, many patients require prescription analgesics to attain relief.
1. van Hecke O, Austin SK, Khan RA, et al. Neuropathic pain in the general population: a systematic review of epidemiological studies. Pain. 2014;155:654-662.
2. Haanpaa M, Rice ASC, Rowbotham MC. Treating herpes zoster and postherpetic neuralgia. Pain Clinical Updates. 2015;23:1-8.
3. Finnerup NB, Attal N, Haroutonian S, et al. Pharmacotherapy for neuropthic pain in adults: a systematic review and meta-analysis. Lancet Neruol. 2015;14:162-173.
4.Veves A, Backonja M, Malik RA. Painful diabetic neuropathy: epidemiology, natural history, early diagnosis, and treatment options. Pain Med. 2008;9:660-674.
5. Schreiber AK, Carina CFM, Reis RC, et al. Diabetic neuropathic pain: physiopathology and treatment. World J Diabetes. 2015;6:432-444.
6. Dimitrova A, Murchison C, et al. Effects of acupuncture on neuropathic pain: A systematic review and meta-analysis. Neurology; 2015;84; Supplement P3.306.