What is the diagnosis and treatment for a patient presenting with a pustular rash on one side of the face?

Unilateral Pustular Facial Rash: Diagnosis and Management

The most likely diagnosis for a pustular rash confined to one side of the face is herpes zoster (shingles), which requires immediate antiviral therapy to prevent complications and reduce morbidity.

Primary Diagnostic Consideration

Herpes zoster should be the leading diagnosis when pustular lesions follow a unilateral, dermatomal distribution on the face. 1 The key distinguishing feature is the strict unilateral presentation respecting the midline, which is pathognomonic for reactivation of varicella-zoster virus along a sensory nerve distribution. 2

Critical Clinical Features to Assess

• Distribution pattern: Pustules following a dermatomal pattern (typically V1, V2, or V3 trigeminal nerve distribution) that stops at the facial midline 1
• Associated symptoms: Prodromal pain, burning, or tingling in the affected dermatome often precedes the rash by 1-5 days 1
• Lesion morphology: Grouped vesicles and pustules on an erythematous base, which may become confluent 3
• Mucosal involvement: Check for oral or ocular involvement, which indicates more severe disease requiring urgent ophthalmology consultation 1

Immediate Management

Antiviral Therapy

Initiate oral acyclovir immediately upon clinical diagnosis without waiting for laboratory confirmation. 1 For patients who appear systemically ill or febrile, or those with mucosal involvement, intravenous acyclovir is indicated. 1

• Start treatment within 72 hours of rash onset for maximum efficacy 1
• Early antiviral therapy reduces acute pain, accelerates healing, and decreases risk of postherpetic neuralgia 1

Supportive Care Measures

• Gentle skin care: Use non-irritating cleansers and avoid frequent washing with hot water 1, 2
• Moisturization: Apply alcohol-free moisturizers containing 5-10% urea twice daily to maintain skin barrier function 1, 2
• Avoid irritants: Do not use over-the-counter anti-acne medications, harsh soaps, solvents, or disinfectants 3, 2

Alternative Diagnoses to Consider

If Drug-Induced Papulopustular Eruption

If the patient is receiving anticancer therapy (EGFR inhibitors, MEK inhibitors), drug-induced papulopustular eruption becomes a consideration, though these typically present bilaterally. 3

Treatment approach for drug-induced rash:

• Grade 1-2: Continue causative medication and initiate oral tetracyclines (doxycycline 100 mg twice daily OR minocycline 100 mg daily) for at least 6 weeks 3
• Topical therapy: Apply low-to-moderate potency corticosteroids (hydrocortisone 2.5% or alclometasone 0.05%) twice daily 3
• Grade 3: Interrupt causative medication until rash improves to grade 1, add systemic corticosteroids (prednisone 0.5-1 mg/kg for 7 days with 4-6 week taper) 3

If Bacterial Superinfection Suspected

Obtain bacterial culture BEFORE initiating antibiotics if infection is suspected. 3 Signs suggesting superinfection include: 3

• Failure to respond to initial treatment
• Presence of painful skin lesions
• Yellow crusts or purulent discharge
• Systemic signs of infection

Administer culture-directed antibiotics for at least 14 days based on sensitivity results. 3, 1

Common Pitfalls to Avoid

• Do not delay antiviral therapy while awaiting laboratory confirmation in suspected herpes zoster—clinical diagnosis is sufficient 1
• Do not use topical anti-acne medications on pustular rashes, as these are irritants that worsen inflammation 3, 2
• Do not assume bilateral distribution is required for drug-induced rashes—while typical, unilateral presentations can rarely occur 3
• Do not overlook ocular involvement in facial herpes zoster, which requires urgent ophthalmology referral to prevent vision loss 1

When to Refer

Urgent dermatology referral is indicated for: 1, 2

• Grade 3-4 severity rashes
• Systemic symptoms (fever, malaise, hypotension)
• Suspected autoimmune skin disease
• No response to first-line treatment after 2 weeks
• Need for skin biopsy for definitive diagnosis

Immediate ophthalmology referral for: 1

• Any ocular symptoms or periorbital involvement in suspected herpes zoster
• Hutchinson's sign (lesions on tip of nose indicating nasociliary nerve involvement)