wiki:infection:viral

due to reactivation of dormant varicella zoster virus, usually after some form of immuno-compromise eg. age, illness, stress
- a mild non-specific 'viral' illness may then precede the rash
- vesicles usually crust over ≤10/7 after rash begins and then no longer infectious
clinical diagnosis usually based on dermatomal pain and eruption of grouped vesicles in the same dermatome with pain usually preceding the rash and therefore making the diagnosis at times.
- most common dermatomes affected: T1-L2. Ophthalmic division of trigeminal affected in around 15% cases
pain can persist for months after rash which will usually last ≤4/52
polymerase chain reaction (PCR) testing of vesicle or other fluids is highly sensitive and specific

analgesia
- simple analgesia and NSAIDs
- amitryptiline, nortriptiline are effective for post-herpetic neuralgia
- gabapentin and pregabalin also useful
- topical agents: lignocaine, capsaicin
anti-virals
- eg acyclovir, effective and best started within 72/24 of rash
  - some debate about whether reduces incidence of post-herpetic neuralgia but probably reduce shedding and healing time if given early (<72/24)
  - 800mg 5 times daily
- Valaciclovir - reported to have greater overall effectiveness than aciclovir as it produces higher levels of antiviral activity in blood
  - 1g tds for 7/7 https://bnf.nice.org.uk/drug/valaciclovir.html
- IV acyclovir for complicated Zoster or ophthalmic zoster
Glucocorticoids
- similar debate as anti-virals about effectiveness
- adjunct to anti-viral Rx, may reduce pain and promotes early healing of rash
Varicella Zoster vaccine available for prevention

Hutchinson’s sign refers to the presence of vesicular lesions on the nose due to involvement of the nasociliary branch of the trigeminal nerve

Also known as herpes zoster oticus - rare complication of shingles involving the geniculate ganglion of the facial nerve.

generally present with lesions in the ear and side of the tongue and facial paralysis.
Other symptoms - loss of taste and, if the vestibulocochlear nerve is affected, vertigo and tinnitus.
may initially be difficult to differentiate from Bell’s palsy, but Bell’s palsy is usually painless and does not affect the ear or tongue.

pharmacological agents
	anti viral
acyclovir	• inhibit HSV polymerase, thereby inhibiting replication • Dose: 800mg 5x daily
valaciclovir	• more effective than acyclovir • Dose: 1000mg tds
	analgesia
simple analgesia	• paracetamol +/- codeine, NSAIDs
anti-convulsants	Gabapentin • GABA analogue but does NOT bind those rec's • excreted unchanged in urine • Dose: d1 = 300mg, d2 = 300mg bd, d3 = 300mg tds then as needed
anti-convulsants	Pregabalin\\• GABA analogue binds to subunit of Ca++ channels in CNS • Dose: 50-100mg tds
tricyclics	amitriptyline • inhibition of serotonin and NorAdrenaline reuptake. May also bind opioid rec's • Dose: 10-25mg daily then titrated to effect

References include
Prevention and Mx of Herpes Zoster - AFP 2017
https://emedicine.medscape.com/article/1132465-treatment
WHO submission for Gabapentin as Rx for neuropathic pain
gabapentin review
https://bnf.nice.org.uk/drug/gabapentin.html
https://reference.medscape.com/drug/lyrica-cr-pregabalin-343368#10
https://bpac.org.nz/BPJ/2014/March/herpes.aspx