Shingles and chickenpox - pathophysiology, presentation, treatment

https://geekymedics.com/chickenpox/ https://geekymedics.com/shingles/ https://emedicine.medscape.com/article/1131785-overview#a3

Which viral agent is responsible for chickenpox?

Varicella zosta virus

Which viral agent is responsible for shingles?

Herpes Zosta virus

What is the mode of transmission for chickenpox virus?

Via droplet spread or direct skin contact with vesicle fluid; virus enters through the upper respiratory tract.

What are the 3 characteristic stages of skin lesions in chickenpox?

• Macule

• Vesicle

• Granular scab

Typical incubation period for chickenpox

10-14 days with up to 4 days of prodrome period

Chickenpox prodrome period symptoms

• High fever (38-39°C) 

• General malaise

• Myalgia

• Anorexia

• Headache

• Nausea

Describe the chickenpox rash

• Begins as small erythematous macules - scalp, face, trunk and proximal limbs

• Macules develop into papules, vesicles and pustules

• Vesicles and pustules crust over in about 5 days

How can VZV virus go on to cause shingles?

Remains dormant in the sensory nerve ganglia of the dorsal root and can reactivate as herpes zoster (shingles) many years later.

Pathophysiology of VZV?

• After initial inhalation of contaminated respiratory droplets, the virus infects the conjunctivae or the mucosae of the upper respiratory tract, ^[6]  with viral proliferation occurring in regional lymph nodes 2-4 days after infection.

• This is followed by primary viremia on days 4-6 post-infection, and a secondary round of viral replication in internal organs, notably the liver and spleen, leading to a secondary viremia 14-16 days post-infection, characterized by diffuse viral invasion of capillary endothelial cells and the epidermis. ^[6]

How does VZV remain latent in the dorsal root and cranial ganglion?

It evades the immune response by downgrading gene expression & reducing expression of cell surface MHC antigens

What can cause the reactivation of VZV as shingles?

Numerous factors such as stress, immunocompromise or intercurrent illness

When reactivation occurs, what does replication of VZV in the effected ganglion lead to?

Leads to ganglionitis (inflammation).

• VZV spreads distally through the sensory nerves of the affected ganglion, producing significant neural inflammation and denervation, which leads to cutaneous symptoms within the corresponding dermatome

How does shingles classically present?

Normally effects a single dermatome (doesn’t cross the midline).

Typically presents with 2-3 days of sharp stabbing pain in affected dermatome followed by acute erythematous vesicular rash (same dermatome)

Describe the shingles rash?

Initially, the shingles rash is typically erythematous and macular, with vesicles appearing within 1-2 days

What is postherpetic neuralgia in shingles?

Pain that persists 1-3 months after the resolution of the rash - risk of PHN increases significantly with age.

• sharp, burning pain in response to non-noxious stimuli

Why does risk of PHN increase with age?

Because there is a relative loss of large nerve fibres.

What is herpes zoster opthalmicus?

A variant of shingles in which the ophthalmic division (V1) of the trigeminal nerve is affected.

It is associated with numerous complications, including corneal ulcers, glaucoma and blindness.

Who should antivirals be offered to for shingles?

• Immunocompromised patients

• Over 50 years old

• Severe disease

• Evidence of HZO

What are the recommended antivirals for shingles?

• Aciclovir

• Famciclovir

• Valaciclovir

Treatment for postherpetic neuralgia?

Paracetamol & NSAIDs

For severe pain, a trial of amitriptyline, duloxetine, gabapentin or pregabalin can be considered

Topical adjuncts such as capsaicin cream or lidocaine patches may also be useful.