Herpes Zoster infection (Shingles) is caused by the reactivation of the virus which causes chickenpox. After one has had chickenpox the virus remains inside the body in an inactive state. Reactivation of the virus produces the typical rash accompanied by pain, numbness, itching, altered sensitivity and skin pigmentation along the distribution of the involved nerve. One in five patients with Herpes Zoster infection develops PHN where the pain persists for more than 120 days (90 days as per WHO) after the onset of rash. PHN commonly affects the chest region (thoracic dermatomes) and the area around the eye (ophthalmic branch of the trigeminal nerve). Approximately 50% of PHN patients recover within a year and the course is variable in the remaining.
Some individuals are more prone to developing PHN and the risk factors can be divided into those relating to the
- Risk of developing Herpes Zoster infection such as increasing age and low immunity
- Risk of persisting pain– Pain preceding the onset of rash, severe pain with widespread rash and old age have been associated with persisting pain (PHN)
PHN is rare in the age group below 50 years and can be generally diagnosed clinically with the history of previous infection and typical rash in the affected area. The rash generally involves only one side and does not cross the midline.
Symptoms of Postherpetic Neuralgia
PHN presents as burning, shooting, throbbing or electric shock like pain in and around the area of rash. Pain may occur on its own or in response to stimuli such as touch. The involved area often develops pins and needles, itching. Increased sensitivity of the area may make daily activities such as taking bath, wearing clothes difficult. As the rash disappears the affected area may develop skin pigmentation and scarring.
Treatment Options for Postherpetic Neuralgia
A combination of different types of medication is used to control pain in PHN and these include:
- Neuropathic Agents. Nerve pain in PHN pain does not respond well to the usual painkiller and special types of painkillers know as neuropathic agents are used. The best suited medication is chosen after a thorough assessment of the individual taking into account the age, pain severity, other medical problems, general health etc. The dose is increased gradually and it can take some time for the full effects to become apparent. Besides pain relief these medications can also help to reduce tingling sensation, improve sleep and quality of life.
- Topical agents. These include various types of gels, creams and patches and have the advantage of fewer side effects. Local anaesthetic patches may be especially useful in cases of increased sensitivity to stimuli such as touch.
- Opioids. Stronger medications such as opioids may be required for severe pain not responsive to the above medications. These drugs are best prescribed by a specialist who is well versed with the available options and it is important that you adhere to the schedule as prescribed by your pain specialist.
Interventions have the potential of providing long term relief and reducing the dose of medications, thereby reducing the side effects. Most of these interventions are administered in day care setting which means that you do not have to stay in the hospital overnight.
Drug infusions- They work by reducing the sensitivity of the nerves transmitting the pain signals. These are low risk options with the potential of significantly reducing the pain for weeks/ months.
Nerve blocks, Dorsal Root Ganglion Block and Epidural injections can be considered depending on the site involved. These procedures are performed using x-ray or ultrasound guidance and involve injection of local anaesthetics and steroids close to the nerves involved.
Sympathetic nerve blocks such as stellate ganglion block are used for severe uncontrolled pain. Sympathetic nerves are special nerves that normally do not carry pain signals normally but can get involved in chronic pain conditions. These blocks are helpful if the pain signals are travelling through these nerves.
Pulsed radiofrequency (PRF). This treatment involves modulating the way pain signals are transmitted and processed. The resulting pain relief can last for weeks/ months. It is performed using special needles and radiofrequency machine under x-ray or ultrasound guidance.
Neuromodulation including Peripheral Nerve Stimulation (PNS), Spinal Cord Stimulation ― PNS is performed by placing the stimulating electrode in close proximity to the involved peripheral nerve. The nerve can be located using ultrasound and stimulation performed either transcutaneously or by using needle placed close to the nerve. More invasive neuromodulation option involves placing electrodes through the skin or in the spine (Spinal cord Stimulators).