There are no official guidelines to assist in answering this question. I will search for relevant research papers instead.
From the Research
Lasting Symptoms of Postherpetic Neuralgia (PHN)
The lasting symptoms of PHN include:
- A constant or intermittent burning, stabbing, or sharp shooting pain with hyperalgesia or allodynia, persisting beyond the healing of herpetic skin lesions 1
- A steady, aching, boring pain and a paroxysmal lancinating pain, usually exacerbated by contact with the involved skin 2
- Pain that persists 1 to 3 months following the rash of herpes zoster (HZ) 2
- Hyperalgesia or allodynia, which can significantly reduce the patient's quality of life 3
Characteristics of PHN
- PHN affects about 50% of patients over 60 years of age and 15% of all HZ patients 2
- Elderly patients are at increased risk of PHN 4
- The pathophysiology of PHN is complex, likely involving both peripheral and central processes 4
Treatment Options for PHN
- First-line treatments for PHN include tricyclic antidepressants, gabapentin and pregabalin, and the topical lidocaine 5% patch 4
- Opioids, tramadol, capsaicin cream, and the capsaicin 8% patch are recommended as either second- or third-line therapies in different guidelines 4
- Interventional pain management options, such as intercostal nerve blocks/neurolysis, stellate ganglion blocks, paravertebral neurolysis, epidural steroid injections, and dorsal root ganglion-radiofrequency ablation, can provide effective and long-lasting pain relief 1
- Conservative measures, such as hot compresses, can also contribute to symptom relief 3