What conditions have a presentation similar to folliculitis, such as red raised pustules?

Differential Diagnosis of Folliculitis-Like Presentations

The key conditions that mimic folliculitis with red raised pustules include furuncles/carbuncles, Malassezia folliculitis, acneiform drug eruptions, pustular psoriasis, and eosinophilic folliculitis in immunocompromised patients.

Bacterial Folliculitis Progression: Furuncles and Carbuncles

Furuncles differ from simple folliculitis by extending deeper through the dermis into subcutaneous tissue, forming small abscesses, while folliculitis remains superficial with pus limited to the epidermis 1.

Distinguishing Features:

• Furuncles present as inflammatory nodules with overlying pustules through which hair emerges, often with dusky central coloration indicating deeper infection 1, 2
• Carbuncles involve multiple adjacent follicles creating a coalescent inflammatory mass with pus draining from multiple follicular orifices, most commonly on the back of the neck in diabetic patients 1
• Regional lymphadenopathy with tender nodes in the drainage area strongly suggests bacterial etiology, particularly S. aureus 2

Critical Warning Signs:

• Dusky central coloration, rapidly expanding erythema, severe pain, systemic toxicity, crepitus, or bullae formation indicate potential progression to necrotizing infection 2

Malassezia (Pityrosporum) Folliculitis

This fungal folliculitis is frequently misdiagnosed as bacterial acne and should be suspected when acneiform eruptions fail antibiotic therapy 3, 4.

Clinical Characteristics:

• Monomorphic, pruritic papules and pustules distributed on the upper trunk, chest, and back 3, 5
• Pruritus is reported by 71.7% of patients, distinguishing it from bacterial acne 4
• Predominantly affects young to middle-aged adults (average age 24.26 years), with 64% being male 4
• 40.5% of patients report history of unsuccessful prior treatment regimens, typically antibiotics 4

Diagnostic Approach:

• Sampling by tape stripping or comedo extractor with microscopic examination identifies monopolar budding yeast cells without hyphae 5
• Consider when new acneiform eruption develops following antibiotic therapy or immunosuppression 4

Drug-Induced Acneiform Eruptions

Papulopustular eruptions from EGFR inhibitors and MEK inhibitors are among the most common drug-related mimickers 1.

EGFR Inhibitor Rash:

• Develops in 75%-90% of patients (all grades) and 10%-20% (grade 3/4) within days to weeks of therapy initiation 1
• Presents as follicular papules and pustules initially on face (forehead, nose, cheeks), potentially progressing to chest and upper back 1
• Associated symptoms include pruritus, stinging, and pain 1
• Bacterial colonization or superinfection develops in up to 38% of cases 1

MEK Inhibitor Rash:

• Occurs in 74%-85% (all grades) and 5%-10% (grade 3/4) of patients 1
• Clinical presentation similar to EGFR inhibitor rashes 1

Eosinophilic Folliculitis

This condition occurs specifically in individuals with advanced HIV disease and presents distinctly from bacterial folliculitis 6.

Defining Features:

• Severely pruritic, sterile, eosinophilic pustules on chest, proximal extremities, head and neck 6
• Elevated serum IgE and peripheral eosinophilia often present concurrently 6

Pustular Psoriasis and Related Conditions

Generalized pustular dermatoses in adults include pustular psoriasis, Reiter's disease, and subcorneal pustular dermatosis 6.

Distribution Patterns:

• Localized pustular eruptions on hands and feet suggest pustulosis palmaris et plantaris or acrodermatitis continua 6
• Facial involvement suggests acne vulgaris, rosacea, or perioral dermatitis 6

Acute Generalized Exanthematous Pustulosis (AGEP)

Medications can cause generalized pustular eruptions presenting as AGEP, or more localized acneiform drug reactions typically involving face, chest, and back 6.

Common Diagnostic Pitfalls

Key Differentiating Features:

• Pruritus strongly suggests Malassezia folliculitis or eosinophilic folliculitis over bacterial causes 3, 6, 4
• Failure to respond to antibiotics should prompt consideration of fungal etiology 3, 4
• Recent medication initiation (especially EGFR/MEK inhibitors, antibiotics) suggests drug-induced or fungal causes 1, 4
• Immunocompromised state broadens differential to include eosinophilic folliculitis and Malassezia folliculitis 6, 5
• Distribution pattern: upper trunk favors Malassezia; face/sebaceous areas favor drug-induced; deeper nodules with dusky centers indicate furuncles 1, 5