Subcutaneous Lidocaine Injection in Acute Herpes Zoster Neuralgia and Post-herpetic Neuralgia

Herpes zoster (HZ; shingles) is a disease associated with inflammation of peripheral nerves, which can progress with acute and chronic pain, and is considered a significant cause of postherpetic neuralgia (PHN). The varicella-zoster virus (VZV) causes a primary infection known as chickenpox. The virus then migrates to spinal and cranial sensory ganglia, becoming latent through nerve axons and possibly via viremia from the skin lesions. In some individuals later in life, the virus reactivates, causing a secondary infection known as HZ. When the virus reactivates, it progresses along the affected sensory nerve, causing neuronal damage, and reaches the corresponding dermatome of the skin, leading to vesicular rashes and pain (1). There are three stages of HZ pain: the acute pain phase (up to one month), the subacute pain phase (30-90 days after lesion healing), and the PHN phase (pain lasting more than 90 days after the rash begins) (2).

Since herpes zoster can be very painful, adequate pain control is essential. The acute neuralgia of HZ typically presents as acute pain in the relevant dermatome, ranging from mild itching, tingling, and allodynia to severe pain, which often occurs before the skin lesions. For mild to moderate pain in acute HZ, paracetamol, non-steroidal anti-inflammatory drugs (NSAIDs), or tramadol can be considered. For moderate pain, opioids such as morphine or oxycodone may be administered. If moderate pain is not controlled by opioids, gabapentin or pregabalin, tricyclic antidepressants, or corticosteroids may be considered as additional treatments (3). Furthermore, in acute HZ, intradermal infiltration of local anesthetics and corticosteroids has been shown to be effective in reducing pain and preventing the development of PHN (4).

The pharmacological treatment of PHN includes a variety of medications such as alpha-2 delta ligands (gabapentin and pregabalin), other anticonvulsants (carbamazepine), tricyclic antidepressants (amitriptyline, nortriptyline), topical analgesics (5% lidocaine patch, capsaicin), tramadol, or other opioids (5). Repetitive intradermal administration of lidocaine and steroids is also used in the treatment of PHN (4).

In this study, it was aimed to demonstrate the effect of subcutaneous lidocaine injection, which is routinely administered in pain clinic, in patients presenting with pain due to acute HZ and PHN, compare its effects in the acute and chronic stages, and investigate its contribution to preventing the development of PHN. The study design and potential risks are explained in the relevant sections.