Postherpetic neuralgia
Postherpetic neuralgia (PHN) is a painful condition that can arise after a shingles outbreak, which is caused by the reactivation of the varicella-zoster virus. Following the resolution of the shingles rash, approximately 10 to 18 percent of individuals may experience persistent pain and other uncomfortable sensations for months or even years. This condition typically affects the peripheral nervous system and is more common in older adults, particularly those over fifty. Symptoms can vary in intensity and may include allodynia, where normal stimuli, like clothing, cause significant discomfort. The underlying mechanisms of PHN involve nerve damage and inflammation caused by the viral infection.
Diagnosis is often straightforward, based on the appearance of the rash and the nature of the pain, and treatment usually begins with primary care providers. Due to the refractoriness of PHN to standard pain medications, a variety of therapies may be employed, including topical treatments, anticonvulsants, and nerve-blocking interventions. While there is no guaranteed way to prevent PHN, early and aggressive treatment of shingles may help reduce the severity and duration of symptoms. Individuals suffering from PHN often face challenges in daily life, including disrupted sleep and social interactions, highlighting the importance of effective management and support.
Postherpetic neuralgia
- ANATOMY OR SYSTEM AFFECTED: Peripheral nervous system, skin
Definition
Postherpetic neuralgia (PHN) is a common, potentially debilitating complication that occurs in 10 to 18 percent of persons with herpes zoster infection, or shingles. PHN is characterized by pain and other unpleasant sensations that persist for months or years after the resolution of the shingles rash.
Causes
Shingles is a painful rash caused by a reactivation of the varicella zoster virus, which remains latent in nerve ganglia for years after a chickenpox episode. Most often, symptoms of active shingles last about one month. A subset of persons subsequently develops PHN and continues to feel pain long after. The proposed pathogenetic mechanisms underlying this phenomenon stem from the intense inflammation associated with this viral infection and include degeneration of neuronal axon and cell body, atrophy of the spinal cord dorsal horn, scarring of dorsal root ganglia, and loss of skin nerve supply in the affected region.
Risk Factors
The risk of developing this complication increases with advancing age, particularly in people aged fifty and older, irrespective of other risk factors. The likelihood of suffering from PHN is also higher in persons who had severe pain or severe rash during the acute episode and in persons who experienced a prodrome of pain in the nerve distribution area before the rash appeared. Additional risk factors include having a weakened immune system, having a chronic condition like diabetes, delaying antiviral treatment for shingles, and have shingles present on the face and torso.
Symptoms
In PHN, persons experience constant or intermittent pain along cutaneous nerves for over thirty days after the lesions have healed. Pain intensity ranges from mild to excruciating. Sometimes, the pain occurs in response to normally innocuous stimuli, such as fabric touching the skin (allodynia). Itching and numbness occur less often. Consequently, the affected person’s quality of life suffers. Sleep and daily activities are affected, often leading to social withdrawal and depression.
Screening and Diagnosis
Usually, the appearance of the rash and the characteristics of pain render the clinical diagnosis simple and straightforward.
Treatment and Therapy
Postherpetic neuralgia is usually managed by a primary care physician and most often resolves within a year. The affected person may be referred to a pain specialist if the neuralgia cannot be controlled rapidly and effectively in primary care.
The condition is difficult to treat because of its refractoriness to the usual analgesics. Early treatment may be more effective than delayed treatment. Persons may benefit from topical anesthetics, topical capsaicin, anticonvulsants, opioids, tricyclic antidepressants (TCAs), and stress reduction techniques.
Interventions such as nerve blocking injections and electrical stimulation may help. As a last resort, surgical sectioning of the affected nerve root can be performed, but surgery itself can induce pain, including a dreaded complication called anesthesia dolorosa.
Prevention and Outcomes
No treatment appears to prevent PHN completely, but some approaches may shorten the duration or lessen the severity of symptoms. Aggressive, early treatment of shingles reduces the likelihood of complications. Studies have shown that the administration of antiviral drugs (especially valaciclovir and famciclovir) attenuates the severity of the infection and the neural damage it causes, thereby reducing the incidence and duration of PHN. Amitriptyline (a TCA) also holds promise in reducing the pain prevalence after herpes zoster.
Bibliography
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