Diagnosing and managing postherpetic neuralgia.

Postherpetic neuralgia (PHN) represents a potentially debilitating and often undertreated form of neuropathic pain that disproportionately affects vulnerable populations, including the elderly and the immunocompromised. Varicella zoster infection is almost universally prevalent, making prevention of acute herpes zoster (AHZ) infection and prompt diagnosis and aggressive management of PHN of critical importance. Despite the recent development of a herpes zoster vaccine, prevention of AHZ is not yet widespread or discussed in PHN treatment guidelines. Diagnosis of PHN requires consideration of recognized PHN signs and known risk factors, including advanced age, severe prodromal pain, severe rash, and AHZ location on the trigeminal dermatomes or brachial plexus. PHN pain is typically localized, unilateral and chronic, but may be constant, intermittent, spontaneous and/or evoked. PHN is likely to interfere with sleep and daily activities. First-line therapies for PHN include tricyclic antidepressants, gabapentin and pregabalin, and the lidocaine 5 % patch. Second-line therapies include strong and weak opioids and topical capsaicin cream or 8 % patch. Tricyclic antidepressants, gabapentinoids and strong opioids are effective but are also associated with systemic adverse events that may limit their use in many patients, most notably those with significant medical comorbidities or advanced age. Of the topical therapies, the topical lidocaine 5 % patch has proven more effective than capsaicin cream or 8 % patch and has a more rapid onset of action than the other first-line therapies or capsaicin. Given the low systemic drug exposure, adverse events with topical therapies are generally limited to application-site reactions, which are typically mild and transient with lidocaine 5 % patch, but may involve treatment-limiting discomfort with capsaicin cream or 8 % patch. Based on available clinical data, clinicians should consider administering the herpes zoster vaccine to all patients aged 60 years and older. Clinicians treating patients with PHN may consider a trial of lidocaine 5 % patch monotherapy before resorting to a systemic therapy, or alternatively, may consider administering the lidocaine 5 % patch in combination with a tricyclic antidepressant or a gabapentinoid to provide more rapid analgesic response and lower the dose requirement of systemic therapies.