The Clinical Syndrome

Postherpetic neuralgia is one of the most difficult pain syndromes to treat. It affects 10% of patients with acute herpes zoster. Although the reason that this painful condition occurs in some patients but not in others is unknown, postherpetic neuralgia is more common in older individuals and appears to occur more frequently after acute herpes zoster involving the trigeminal nerve, as opposed to the thoracic dermatomes. Conditions that cause vulnerable nerve syndrome, such as diabetes, may also predispose patients to develop postherpetic neuralgia. Recent neuroimaging studies have shown that patients suffering from postherpetic neuralgia have abnormal central pain processes. And peripheral nerve pain specialists agree that aggressive treatment of acute herpes zoster can help prevent postherpetic neuralgia.

Signs and Symptoms

As the lesions of acute herpes zoster heal, the crust falls away, leaving pink scars that gradually become hypopigmented and atrophic. The affected cutaneous areas are often allodynic, although hypesthesia and, rarely, anesthesia may occur. In most patients, the sensory abnormalities and pain resolve as the skin lesions heal. In some patients, however, pain persists beyond lesion healing.

The pain of postherpetic neuralgia is characterized as a constant dysesthetic pain that may be exacerbated by movement or stimulation of the affected cutaneous regions ( Fig. 71.1 ). Sharp, shooting neuritic pain may be superimposed on the constant dysesthetic pain. Some patients suffering from postherpetic neuralgia also note a burning component, reminiscent of reflex sympathetic dystrophy.

Allodynia and dysesthesia are characteristic of postherpetic neuralgia.

Testing

In most cases, the diagnosis of postherpetic neuralgia is made on clinical grounds. Testing is generally used to evaluate other treatable coexisting conditions, such as vertebral compression fractures, or to identify any underlying disease responsible for the patient’s immunocompromised state. Such testing includes basic laboratory screening, rectal examination, mammography, and testing for collagen vascular diseases and human immunodeficiency virus infection. Skin biopsy may confirm the presence of previous infection with herpes zoster if the history is in question.