What is the likely diagnosis for an elderly patient with shoulder pain and blisters on the shoulders, upper arm, and breast?

Herpes Zoster (Shingles)

The most likely diagnosis is herpes zoster (shingles), which classically presents as unilateral dermatomal pain with vesicular blisters in elderly patients, and requires prompt antiviral therapy to reduce acute symptoms and prevent postherpetic neuralgia. 1, 2, 3

Clinical Presentation

• Unilateral dermatomal distribution of pain and blisters affecting the shoulders, upper arm, and breast strongly suggests herpes zoster involving cervical and/or thoracic dermatomes 1, 3, 4
• Prodromal symptoms including pain, itching, and malaise commonly precede the rash by several days 1
• The elderly population is at highest risk, with incidence rising to 10/1000 per year by age 80, and approximately 50% of individuals reaching 90 years will have experienced herpes zoster 1
• Diagnosis is typically clinical based on the characteristic unilateral dermatomal pain and vesicular rash pattern 1, 2, 3

Immediate Management

Antiviral therapy should be initiated as soon as possible (ideally within 72 hours of rash onset) to reduce acute pain, hasten rash healing, and reduce the risk of postherpetic neuralgia 1, 2

• Adequate analgesia during the acute phase may require strong opioid drugs for severe pain 1
• Tricyclic antidepressants (such as nortriptyline) initiated during the acute phase may reduce the risk of postherpetic neuralgia, though firm evidence is limited 1

Risk of Postherpetic Neuralgia (PHN)

Elderly patients face the highest risk of developing PHN, defined as significant pain or dysesthesia persisting ≥3 months after the rash resolves 1, 5, 3

• More than 5% of elderly patients will have PHN at 1 year after acute herpes zoster 1
• Predictors of PHN include greater age, acute pain and rash severity, prodromal pain, presence of virus in peripheral blood, and adverse psychosocial factors 1
• PHN is highly resistant to treatment and can severely impact quality of life and functional ability in the elderly 5, 3

Critical Pitfalls to Avoid

• Do not delay antiviral therapy while awaiting laboratory confirmation—clinical diagnosis is sufficient and early treatment (within 72 hours) is critical for optimal outcomes 1, 2, 4
• Do not undertreat acute pain, as inadequate pain control during the acute phase may increase the risk of developing chronic postherpetic neuralgia 1
• Recognize that oral steroids show no protective effect against postherpetic neuralgia and should not be relied upon for prevention 1
• Be aware that patients with herpes zoster can transmit the virus to non-immune individuals, causing varicella (chickenpox), though herpes zoster itself is not contracted from others with varicella or herpes zoster 1

Differential Considerations

While the clinical presentation strongly suggests herpes zoster, bullous pemphigoid should be considered if blisters are bilateral, non-dermatomal, or lack the characteristic pain pattern, particularly since it is the most common immunobullous disease in elderly patients 6. However, the unilateral dermatomal distribution with pain makes herpes zoster far more likely in this clinical scenario.