Herpes Zoster
Definition: Herpes zoster, also known as shingles, is a localized, painful, blistering rash that is caused by a reactivation of the varicella-zoster virus.
Etiology: The varicella-zoster virus (VZV) is a member of the Herpesvirales order of double-stranded DNA viruses, that causes chickenpox. The VZV establishes latency in the dorsal root ganglia nerve cells of the spinal cord after primary infection. Once reactivated, the virus replicates in neuronal cell bodies and migrates down sensory nerves to the skin, causing herpes zoster. Pain associated with zoster is due to inflamed nerves that are affected by the virus. The virus can be transmitted via skin-to-skin contact or droplet inhalation.
Epidemiology: The incidence of herpes zoster is 1.2- 3.4 per 1000 persons per year in individuals younger than 65 years. In individuals older than 65 years, the incidence is 3.9- 11.8 per 1000 persons per year. Recurrences are often seen in immunocompromised patients.
Signs: The dermatological involvement of herpes zoster is centripetal and follows a dermatomal distribution pattern. This is typically unilateral and may vary depending on the affected dermatome, age and health of the patient. Following the onset of pain, the rash that erupts is a crop of red papules that is painful, erythematous and blistering. On dark skin, the “shingles band” may appear as gray, dark brown or violaceous papules. The rash then develops forming vesicles which can cause discolouration of the surrounding skin depending on skin tone.The lesions continue to erupt and become pustular and crust over.
Symptoms: Early symptoms include localized or widespread pain without tenderness or skin changes. The zoster rash is painful within the associated area of skin. Individuals may feel unwell with a fever and headache. In uncomplicated cases, pain and general symptoms subside as the eruption disappears.
Differentials: Herpes simplex, dermatitis herpetiformis, impetigo, contact dermatitis, candidiasis.
Diagnosis: Herpes zoster is diagnosed clinically with pain, characteristic morphology and dermatomal distribution. The rash may form a pattern called the zosteriform herpes simplex. Diagnostic tests include direct fluorescent antibody, PCR and Tzanck smear of vesicular fluid or blood.
Treatment: Several antiviral drugs are available to treat shingles such as acyclovir and valacyclovir. They shorten the length and severity of illness. Over-the-counter pain relief medication can also aid in the pain caused by shingles. The CDC recommends 2 doses of the recombinant zoster vaccine to prevent shingles and its complications in individuals 50 years and older. Vaccination is also recommended in younger, immunocompromised patients.
References:
- Nair PA, Patel BC. Herpes Zoster. In: StatPearls. Treasure Island (FL): StatPearls Publishing; September 4, 2023.
- Ayoade F, Kumar S. Varicella-Zoster Virus (Chickenpox). In: StatPearls. Treasure Island (FL): StatPearls Publishing; October 15, 2022.
- Herpes zoster | DermNet NZ. dermnetnz.org. https://dermnetnz.org/topics/herpes-zoster
- CDC. Shingles. Centers for Disease Control and Prevention. Published 2019. https://www.cdc.gov/shingles/about/index.html