How to differentiate and treat herpes zoster (shingles) vs impetigo on the face?

Differentiating and Treating Herpes Zoster vs Impetigo on the Face

Herpes zoster presents with prodromal pain 24-72 hours before a unilateral vesicular eruption in a dermatomal distribution, while impetigo shows honey-colored crusts or flaccid bullae without dermatomal pattern or preceding pain, and treatment differs fundamentally: oral antivirals (valacyclovir 1 gram three times daily for 7 days) for herpes zoster versus topical mupirocin or oral anti-staphylococcal antibiotics for impetigo. 1, 2, 3

Clinical Differentiation

Herpes Zoster (Shingles) Key Features:

• Prodromal symptoms: Pain, burning, or abnormal sensations precede the rash by 24-72 hours in the affected dermatome 1, 4
• Distribution: Strictly unilateral, confined to a single dermatome (commonly trigeminal nerve distribution on the face) 1, 4
• Lesion progression: Erythematous macules → papules → clear vesicles that become cloudy → crusting over 7-10 days 1, 4
• Vesicle characteristics: Grouped vesicles on an erythematous base that may coalesce 1
• Timeline: Lesions continue erupting for 4-6 days in immunocompetent hosts, with total disease duration approximately 2 weeks 1

Impetigo Key Features:

• No prodromal pain: Lesions appear without preceding neuralgic symptoms 2, 5
• Distribution: No dermatomal pattern; typically affects exposed areas like face and extremities, often bilateral or scattered 2, 5
• Nonbullous impetigo (70% of cases): Erythematous papules → vesicles → pustules → honey-colored crusts on erythematous base 2, 5
• Bullous impetigo (30% of cases): Large, flaccid, thin-roofed bullae that rupture creating crusted erosions, often with a collar of remnant roof 2, 5
• No scarring: Both types resolve within 2-3 weeks without scarring (unlike ecthyma, which does scar) 2, 5

Diagnostic Pitfalls and Caveats

Critical distinction: The presence or absence of dermatomal distribution and prodromal pain are the most reliable differentiating features 1, 4. However, be aware of these confounding scenarios:

• Atypical herpes zoster: May present with nonspecific lesions without classic vesicular appearance initially, or the rash may be faint or evanescent 1
• Zosteriform impetigo: Rare cases of S. aureus impetigo can occur in a dermatomal pattern (Wolf's isotopic response in a cutaneous immunocompromised district from prior herpes zoster), but these lack prodromal pain 6
• Immunocompromised patients: Herpes zoster may have atypical presentation with prolonged eruption period (7-14 days) and slower healing 7

Confirmatory Testing When Needed

For typical presentations, clinical diagnosis alone is sufficient 1, 4. Obtain confirmatory testing in these situations:

For Suspected Herpes Zoster:

• Immunocompromised patients with atypical presentation 8
• Absence of characteristic pain or dermatomal distribution 1
• Testing options: Vesicle fluid for PCR (most sensitive), direct fluorescent antibody testing, or viral culture 1, 6
• Tzanck smear showing multinucleated giant cells supports herpesvirus infection but doesn't distinguish HSV from VZV 1

For Suspected Impetigo:

• Culture of vesicle fluid, pus, or erosions to establish causative organism (S. aureus vs Streptococcus pyogenes) 2
• Culture is particularly important when MRSA is suspected or in outbreak settings 2, 5

Treatment Algorithms

Herpes Zoster Treatment:

Initiate antiviral therapy within 72 hours of rash onset (most effective within 48 hours) 3, 4:

First-line oral antivirals (choose one):

• Valacyclovir 1 gram three times daily for 7 days (preferred for better bioavailability and less frequent dosing) 3
• Acyclovir 800 mg five times daily for 7-10 days 8
• Famciclovir 500 mg three times daily for 7 days 9

Special considerations for facial involvement:

• Facial zoster requires particular attention due to risk of cranial nerve complications 8
• Elevation of affected area to promote drainage 8
• Keep skin well-hydrated with emollients to prevent cracking 8

Escalate to IV therapy if:

• Disseminated or invasive disease 8
• Immunocompromised host with severe disease 8, 7
• IV acyclovir is the treatment of choice for severely compromised hosts 8, 7

Adjunctive therapy:

• Analgesics for acute neuritis (may require amitriptyline or gabapentin for severe pain) 10, 4
• Prednisone may be considered as adjunctive therapy in select cases of severe, widespread disease, but avoid in immunocompromised patients 8

Impetigo Treatment:

For limited lesions (few lesions, localized):

• Topical mupirocin (first-line, most effective topical agent) 2, 5
• Alternative: Retapamulin 2, 5
• Avoid: Bacitracin and neomycin (considerably less effective) 2

For extensive lesions (numerous lesions, facial involvement, or outbreak settings):

Oral antibiotics active against both S. aureus and streptococci (unless culture shows streptococci alone):

• Cephalexin (first-generation cephalosporin) 2
• Dicloxacillin (penicillinase-resistant penicillin) 2
• Amoxicillin-clavulanate 5

For penicillin allergy or suspected MRSA:

• Clindamycin 2, 5
• Trimethoprim-sulfamethoxazole (covers MRSA but inadequate for streptococcal infection alone) 2, 5
• Doxycycline or minocycline 2, 5

If streptococci alone (confirmed by culture):

• Penicillin is drug of choice 2
• Macrolide or clindamycin for penicillin allergy 2

Important caveat: Systemic therapy is preferred for numerous lesions or outbreaks to decrease transmission 2. Reevaluate patients in 24-48 hours if using empiric therapy to verify clinical response 2.

Histopathological Correlation

If biopsy is performed for atypical presentations:

Herpes zoster: Acantholysis, ballooning degeneration, intranuclear viral inclusions, multinucleated giant cells, and intraepidermal vesicle formation 11

Impetigo: Subcorneal or intraepidermal pustules with neutrophils, gram-positive cocci on Gram stain, without viral cytopathic changes 2