Clues Pointing TO This Diagnosis

Prior chickenpox in childhood — herpes zoster is reactivation of latent varicella-zoster virus from the initial varicella infection
Age 68 — incidence and severity of zoster rise sharply with age due to waning cell-mediated immunity
Prodrome of burning pain on the left chest before any rash — dermatomal pain preceding lesions by 1–5 days is characteristic
Nothing visible for the first few days — the classic prodrome occurs before the cutaneous eruption appears
Grouped vesicles appearing 3 days after the pain — evolution from pain to clustered vesicles is the typical time course
Rash in a stripe following one dermatome across the ribs — unilateral, single-dermatome distribution is the hallmark
Rash does not cross the midline — VZV travels down a single sensory nerve, so lesions stop at the midline
Pain, burning, and itching with the eruption — acute zoster-associated pain is often severe
Vesicles crusting over about 3 weeks — lesions progress to pustules/crust and heal within 2–4 weeks
Persistent burning pain after the rash healed — postherpetic neuralgia, the most common complication

Why It's NOT the Similar Diseases

NOT herpes simplex — HSV recurs at the same site (usually orolabial or genital) and is not confined to a single thoracic dermatome in a stripe that stops at the midline as Otis's rash is
NOT contact dermatitis — contact dermatitis is pruritic, follows exposure patterns, and is not dermatomal or preceded by a burning neuralgic prodrome
NOT cellulitis — cellulitis is a spreading confluent area of warmth and erythema without grouped vesicles or a strict dermatomal boundary
NOT a cardiac/coronary event — Otis's left-sided chest pain is superficial, burning, and followed by a dermatomal vesicular rash rather than exertional pressure with ischemic ECG changes
NOT bullous impetigo — impetigo produces honey-crusted or bullous lesions in a non-dermatomal distribution and is not preceded by neuralgic pain

Differential Diagnosis List

Herpes simplex virus — ruled out by strict single-dermatome distribution not crossing midline
Contact dermatitis — ruled out by dermatomal pattern and neuralgic prodrome
Cellulitis — ruled out by grouped vesicles and dermatomal boundary rather than confluent spreading erythema
Cardiac chest pain — ruled out by superficial burning pain followed by a vesicular dermatomal rash
Bullous impetigo — ruled out by preceding neuralgic pain and dermatomal vesicle clustering

Key Distinguishing Test

Herpes zoster is a clinical diagnosis in the vast majority of cases, based on the characteristic unilateral, dermatomal vesicular eruption preceded by neuralgic pain.
When confirmation is needed (atypical, disseminated, or immunocompromised presentations), polymerase chain reaction (PCR) of a vesicle swab for VZV DNA is the most sensitive and specific confirmatory test.

Board Note

Start oral antivirals (valacyclovir, famciclovir, or acyclovir) as early as possible, ideally within 72 hours of rash onset; valacyclovir and famciclovir are preferred over acyclovir for less frequent dosing—antivirals speed healing and reduce acute pain
Treat beyond the 72-hour window if new lesions are still forming or complications are present
Postherpetic neuralgia (dermatomal pain persisting ≥90 days) is the most common complication, affecting about 1 in 5 patients, and is treated with gabapentin/pregabalin, tricyclic antidepressants, or topical lidocaine/capsaicin—antivirals do not reliably prevent it
Refer any patient with V1 (ophthalmic) involvement—including lesions on the nose tip (Hutchinson sign) or new eye symptoms—urgently to ophthalmology
Advise contact precautions: lesions are infectious to varicella-susceptible people until fully crusted
Prevent with the recombinant zoster vaccine (Shingrix), a 2-dose series for all immunocompetent adults ≥50 years (and immunocompromised adults ≥19), >90% effective—recommended even after an episode of zoster and regardless of prior chickenpox or Zostavax
The following NEJM figure maps the natural history of VZV from chickenpox through latency to reactivation and its neurologic complications, including postherpetic neuralgia:
Figure 1. Neurologic Complications of the Reactivation of Varicella–Zoster Virus.
Neurologic Complications of the Reactivation of Varicella–Zoster Virus. N Engl J Med. March 1, 2000.
Used under license from The New England Journal of Medicine.

“Otis’s Story”