Postherpetic neuralgia

Postherpetic neuralgia has a significant negative impact on the quality of life and functional status of patients, who may develop affective disorders in the form of anxiety, depression, as well as disturbances in social activity, sleep, and appetite. Taking into account all these factors is very important in the treatment of patients with postherpetic neuralgia.

After chickenpox, the Herpes zoster virus remains in the body in a latent state, localizing primarily in the sensory ganglia of the spinal nerves and the trigeminal nerve. When reactivated, the virus causes the formation of a characteristic vesicular rash and the appearance of pain in the innervation zone of the corresponding nerve root.

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Symptoms of postherpetic neuralgia

In 50% of patients, the rash is localized on the trunk, in 20% - on the head, in 15% - on the arms, in 15% - on the legs. After a few days, the rash transforms into a pustular rash, then forms crusts and disappears by the end of the 3-4th week. However, many patients experience severe pain in the affected dermatome for several months and even years after the rash disappears. This pathological condition is called postherpetic neuralgia (PHN). Herpetic neuralgia develops especially often in patients over 60 years of age (50%). The pain is associated with inflammatory changes in the ganglia of the posterior roots of the spinal cord and peripheral nerves (the leading pathophysiological mechanisms are ectopic activity, expression of sodium channels on the membranes of nerve cells, and central sensitization).

Patients with postherpetic neuralgia may experience three types of pain: constant, deep, dull, pressing or burning; spontaneous, intermittent, stabbing or shooting (“electric shock”); and allodynic (sharp, superficial, burning, usually occurring with light touch).

In most patients, the pain associated with postherpetic neuralgia subsides within 1 year. However, in some patients, it may persist for years or even for the rest of their lives.

Treatment of postherpetic neuralgia

In terms of treatment of postherpetic neuralgia, timely treatment of herpes in the acute period with antiviral drugs (acyclovir, famciclovir and valacyclovir) plays an important role. Studies have shown that all 3 of the above drugs reduce pain associated with herpes zoster and the risk of developing postherpetic neuralgia. Antidepressants, local anesthetics and anticonvulsants are used for symptomatic treatment of pain associated with postherpetic neuralgia.

• Tricyclic antidepressants (amitriptyline at a dose of up to 150 mg/day) are most often used. Given the predominantly elderly age of patients with postherpetic neuralgia, when prescribing tricyclic antidepressants, it is important to strictly take into account their side effects.
• Several randomized studies have demonstrated the effectiveness of lidocaine patches. Transdermal delivery of local anesthetic directly to the area of pain localization allows for effective pain relief. Unlike drugs used for local analgesia in the form of ointment or gel, this dosage form has an undeniable advantage in ease of use (the patch is easily applied to the site of pain, does not stain clothing, etc.). In addition, the patches protect the painful area from external irritants (touch of clothing, etc.), which is very important since most patients experience allodynia. Undesirable side effects in the form of skin reactions (itching and redness of the skin) usually disappear spontaneously within a few hours after stopping treatment. Another topical drug, capsaicin, is rarely used today because it usually increases pain at the beginning of treatment by activating nociceptive A5 and C fibers (pain relief occurs later due to desensitization of nociceptors in the peripheral terminals of sensory nerves).
• Of the anticonvulsants, gabapentin and pregabalin have proven to be the most effective in the treatment of postherpetic neuralgia. Gabapentin is prescribed at a dose of 300 mg on the 1st day, 600 mg (in 2 doses) on the 2nd day, 900 mg (in 3 doses) on the 3rd day. If necessary, the dose is increased to 1800-3600 mg/day (in 3 doses). The recommended dose of pregabalin is 75 to 150 mg 2 times a day or 50 to 100 mg 3 times a day (150-300 mg/day). If there is no satisfactory effect after 2-4 weeks of treatment, the dose is increased to 600 mg/day.