Pustular Skin Conditions: Diagnosis, Causes, Treatment Guide

Pustular skin conditions are characterized by the presence of pustules, which are small, circumscribed elevations of the skin filled with neutrophilic pus. These can arise from infectious or non-infectious (sterile) causes. Sterile pustules result from inflammatory dermatoses, while infectious ones stem from bacterial, fungal, or viral agents. Accurate differentiation is crucial for appropriate management, often requiring clinical evaluation, swabs, and skin biopsy.

What are pustules?

A

pustule

is a visible collection of pus within or beneath the epidermis, typically 1–10 mm in size, often with an erythematous base. Pus comprises neutrophils, debris, and serum. Pustules may be superficial (subcorneal) or deeper (intraepidermal or subepidermal). Sterile pustules lack microorganisms and indicate primary neutrophilic inflammation, common in conditions like pustular psoriasis. Infectious pustules contain pathogens and require antimicrobial therapy.

Sterile pustules

Sterile pustules predominate in autoimmune or inflammatory disorders. Key conditions include:

• Generalized pustular psoriasis (GPP): Rare, severe form with widespread sterile pustules on erythematous skin, often von Zumbusch type. Triggers include steroids withdrawal, infections, pregnancy. Systemic symptoms: fever, fatigue, tachycardia.
• Palmoplantar pustulosis: Chronic, recurrent pustules on palms/soles, associated with psoriasis or SAPHO syndrome.
• Acrodermatitis continua of Hallopeau: Continuous pustules on digits, leading to nail dystrophy; psoriasis variant.
• Subcorneal pustular dermatosis (Sneddon-Wilkinson): Flaccid superficial pustules in annular/circinate patterns on trunk/flexures, IgA-mediated.
• Acute generalized exanthematous pustulosis (AGEP): Drug-induced, widespread nonfollicular pustules with fever; resolves in 2 weeks.
• Infantile acute haemorrhagic oedema of infancy: Rare in infants, annular purpuric plaques with pustules.
• Erythema annulare centrifugum with pustulation: Pustules at expanding annular borders.
• Pustular vasculitis: Hypopyon-like or vesiculopustular lesions on lower legs.

Infectious pustules

Infectious pustules harbour pathogens. Common causes:

• Bacterial folliculitis/impetigo: Staphylococcal/streptococcal; superficial/deep follicular pustules.
• Candidiasis: Satellite pustules in flexures.
• Tinea incognito: Modified pustular ringworm due to steroids.
• Herpes infections: Grouped pustular vesicles.
• Miliaria pustulosa: Retained sweat in hot climates.

Differential diagnosis

Differentiating sterile from infectious pustules relies on history, morphology, distribution, and tests. Sterile pustules are monomorphic, nonfollicular, widespread in GPP/AGEP; infectious are polymorphic, follicular, localized.

Feature	Sterile Pustules	Infectious Pustules
Morphology	Monomorphic, subcorneal/intraepidermal	Polymorphic, follicular/vesicular
Distribution	Widespread/flexural (GPP, AGEP)	Localized (follicles, trauma sites)
Systemic signs	Fever, neutrophilia in severe cases	Lymphadenopathy, suppuration
Swab/biopsy	Sterile neutrophils, spongiform pustules	Pathogens cultured/seen

Investigations

• Clinical assessment: History of triggers (drugs, pregnancy), morphology, Nikolsky sign.
• Swabs/Scrapes: Gram stain, culture, fungal/viral PCR for infection.
• Skin biopsy: Gold standard. Sterile: Kogoj spongiform pustules (psoriasis), subcorneal pustules (Sneddon-Wilkinson). Special stains for organisms.
• Bloods: FBC (neutrophilia), CRP, LFTs, cultures in systemic disease.

Management

Treatment targets underlying cause. Supportive care essential for severe GPP (hydration, electrolytes).

Sterile pustules

• Generalized pustular psoriasis: Acitretin, cyclosporine, methotrexate, biologics (IL-17/IL-36 inhibitors like spesolimab). Avoid systemic steroids.
• Palmoplantar/Acrodermatitis: Topical steroids, calcipotriol, phototherapy, acitretin.
• Subcorneal pustular dermatosis: Dapsone first-line; sulfapyridine, retinoids.
• AGEP: Withdraw culprit drug; topical steroids, antihistamines.

Infectious pustules

• Bacterial: Topical/systemic antibiotics (mupirocin, flucloxacillin).
• Fungal: antifungals (azoles).
• Viral: antivirals (acyclovir).

Frequently Asked Questions (FAQs)

Q: Are pustules always infected?

A: No, many are sterile from inflammatory conditions like pustular psoriasis. Biopsy distinguishes them.

Q: What triggers generalized pustular psoriasis?

A: Steroids withdrawal, infections (COVID-19, strep), pregnancy, stress.

Q: Is pustular psoriasis contagious?

A: No, pustules are sterile and non-contagious.

Q: How is subcorneal pustular dermatosis treated?

A: Dapsone is highly effective; monitor for haemolysis.

Q: When should I seek urgent care for pustules?

A: If widespread with fever, dehydration, or systemic symptoms suggestive of GPP.

This article provides an overview; consult a dermatologist for personalized advice. Early diagnosis improves outcomes in these potentially severe conditions.