What is the appropriate emergency department workup for a patient with suspected herpes zoster (shingles)?

Emergency Department Workup for Suspected Shingles

Shingles is primarily a clinical diagnosis based on the characteristic unilateral dermatomal vesicular rash, and laboratory workup is generally not required in immunocompetent patients with typical presentations. 1, 2

Clinical Diagnosis Approach

The diagnosis should be made by history and physical examination in the vast majority of cases. 3 The key diagnostic features include:

• Prodromal pain that precedes skin findings by 24-72 hours, characterized by burning, itching, tingling, or paresthesia localized to a single dermatome 2
• Unilateral vesicular eruption in a dermatomal distribution, progressing from erythematous macules to papules and then to vesicles 2
• Lesions that continue to erupt for 4-6 days in immunocompetent hosts, with total disease duration of approximately 2 weeks 2

When Laboratory Testing IS Indicated

Laboratory confirmation should be obtained in specific situations only 2:

• Atypical presentations where the rash is nonspecific, localized, faint, or evanescent 2
• Immunocompromised patients (HIV, active chemotherapy, organ transplant recipients, chronic immunosuppression) 4, 2
• Diagnostic uncertainty or absence of characteristic pain 2
• Multidermatomal involvement raising concern for disseminated disease 1

Diagnostic Testing Options (When Indicated)

When testing is necessary, the following modalities are available 4:

• PCR testing of vesicle fluid (most sensitive and specific, approaching 100%) - can detect VZV DNA even in crusted lesions 4
• Direct immunofluorescence antigen testing from vesicle fluid 4
• Tzanck smear showing multinucleated giant cells (does not differentiate VZV from HSV) 4
• Viral culture from vesicle fluid (less commonly used due to longer turnaround time) 4

Important caveat: Serology is not useful for diagnosis of active shingles 4

Additional Workup Considerations

Risk Factor Screening

Consider screening for underlying conditions in appropriate patients 2:

• HIV testing in younger patients or those with severe/recurrent disease
• Diabetes screening
• Malignancy evaluation if clinically indicated
• Review of immunosuppressive medications

Complications Assessment

Evaluate for complications requiring escalation of care 1, 2:

• Ophthalmic involvement (trigeminal/V1 distribution) - requires urgent ophthalmology referral 4
• Disseminated disease (≥3 dermatomes, visceral involvement, hemorrhagic lesions) - requires IV acyclovir 1
• CNS complications (encephalitis, meningitis) - requires IV acyclovir and neuroimaging 1
• Elevated liver enzymes suggesting VZV hepatitis - requires IV therapy 1

What NOT to Order

• Blood cultures have no role in diagnosing localized herpes zoster in immunocompetent patients with unremarkable systemic examination 2
• Skin biopsy is not indicated for typical presentations and is reserved for immunocompromised patients with atypical lesions 2
• Serologic testing (VZV IgG/IgM) does not help diagnose acute shingles 4

Practical ED Management Algorithm

For typical presentation in immunocompetent patient:

1. Make clinical diagnosis without laboratory testing 2, 3
2. Initiate oral antiviral therapy (valacyclovir 1g TID or acyclovir 800mg 5x daily) within 72 hours of rash onset 1, 5
3. Discharge with pain management and follow-up instructions 1

For atypical presentation or immunocompromised patient:

1. Obtain PCR or direct immunofluorescence from vesicle fluid 4
2. Consider HIV testing and screening for immunosuppression 2
3. Initiate empiric antiviral therapy while awaiting results 1
4. Consider admission for IV acyclovir if disseminated or severe disease 1

For facial/ophthalmic involvement:

1. Urgent ophthalmology consultation before discharge 4
2. Initiate oral antivirals immediately 1
3. Consider admission if V1 distribution with eye involvement 1