THM 1) Zoster can occur at any site of the body but most frequently affects thoracic or lumbar segments (T3-L2) and the trigeminal nerve (V1-3).
THM 2) In some cases cutaneous lesions may develop without any significant pain. Conversely there may be intense pain without skin findings (zoster sine herpete).
THM 3) ‘Isotropic response’ may be seen in zoster. In skin that’s damaged, months to years later, diseases like warts, molluscum, tinea, lichen planus or basal cell carcinoma may appear.
THM 4) Post herpetic neuralgia is defined as pain persisting for more than 1 month after eruption of zoster. The pain may also develop after a pain free interval. Post herpetic neuralgia occurs in about 15% of all zoster patients and in 50% of patients >50 years of age. It is also more common in patients with pain during prodromal or acute phase of zoster or if cranial or sacral dermatomes are involved.
THM 5) During chicken pox, the VZV (varicella zoster virus) passes from the skin lesions into cutaneous sensory nerve endings and ascends up to the sensory ganglia. The VZV then remains dormant in cranial nerves sensory ganglia and /or spinal dorsal root ganglia. This dormant virus reactivates as herpes zoster in 10-30% of patients. Upon reactivation (which may be triggered by trauma, stress, exhaustion, steroids, immune suppression etc.) the virus travels back from the ganglion to the skin.
THM 6) Zoster rash may be preceded by prodrome of burning, tingling, itching or pain in involved dermatome, often accompanied by tenderness/hyperaesthesia of skin. The prodrome of zoster usually precedes the rash by 2-4 days and the symptoms may continue for several days after the rash has appeared.
THM 7) Pain and vesicles in external ear canal suggest Ramsay Hunt syndrome – reactivation of zoster in genticulate ganglion of the sensory branch of facial nerve.
Besides vesicles in external ear canal, features of Ramsay hunt syndrome are:
1) Ipsilateral facial palsy.
2) Loss of taste in anterior 2/3 rd of tongue.
THM 8) Ideally, oral antivirals for zoster should be started in 72 hours of rash onset.
THM 9) Patients with zoster can transmit infection (causing chicken pox) in non immune contacts espically children, who should therefore not be allowed close contact.
THM 10) Chicken pox does NOT confer immunity against zoster in adulthood. In fact chicken pox is the reason you get zoster later.
THM 11) A vaccine against herpes zoster is available in the U.S. as ‘Zostavax’. It is more potent than the routine chicken pox vaccine. It is not available here. Zostavax is recommended in persons >60 years irrespective of past history of chickenpox or zoster. It reduces incidence of zoster and severity of PHN if zoster occurs.
THM 12) To summarize treatment of zoster in an adult-
1) If patient comes within 72 hours of onset of rash, start valacyclovir 1g tds. Optional antivirals include acyclovir and famciclovir.
2) May start valacyclovir even AFTER 72 hours if rash is severe or patient is immune compromised eg. AIDS.
3) Treatment for minimum 7 days or till all vesicles disappear.
4) Avoid local applications or systemic antibiotics unless vesicles have secondary infection.
5) If eye is involved, refer immediately to an ophthalmologist.
THM 13) For pain DURING rash, we use analgesics eg. tramadol 50mg tds. If pain is severe and patient >65 one may consider oral steroids to be given with valacyclovir. When given for acute zoster pain, starting dose of prednisolone is 1mg/kg/d. It reduces intensity and period of pain. Duration and tapering are individualized.
THM 14) Since acute zoster pain can last several days and PHN is defined as pain > 4 weeks, start amitriptyline like drugs only if pain continues beyond 4 weeks. Treatment of PHN- amitriptyline-start 20mg/d and titrate to at least 75mg. Side effects of amitriptyline are sedation, constipation, mouth dryness, weight gain etc. Need to give for weeks to months. More expensive alternatives to amitriptyline are pregabalin and gabapentin . Start pregabalin at 75mg/d and go up to 300mg/d if tolerated. Side effects are oedema, weight gain, sedation.