Definition of Large Pustules in Dermatology
In dermatology, pustules are generally considered large when they reach a diameter of 5 mm or greater. 1
Characteristics and Classification of Pustules
Pustules are defined as circumscribed collections of purulent material within the skin. They can be categorized based on their size:
- Small pustules: Less than 5 mm in diameter
- Large pustules: 5 mm or greater in diameter 1
This 5 mm threshold is particularly important in clinical contexts such as:
Acne classification: In severe nodular acne, inflammatory lesions with a diameter of 5 mm or greater are classified as nodules, which may become suppurative (pustular) or hemorrhagic 1
Fistula assessment: In inflammatory bowel disease, collections of fluid with diameter >10 mm are specifically highlighted as "abscesses" and may require surgical intervention 2
Clinical Significance of Large Pustules
The size of pustules has important implications for diagnosis and treatment:
- Diagnostic significance: Large pustules (≥5 mm) often indicate more severe inflammatory processes or specific conditions
- Treatment implications: Larger pustules may require different management approaches than smaller ones
- Disease severity marker: The presence of large pustules is often used as a criterion for classifying disease severity, as seen in the indication for isotretinoin in severe nodular acne 1
Differential Considerations
When evaluating large pustules, consider:
- Infectious causes: Bacterial, fungal, or viral infections
- Non-infectious causes:
- Inflammatory conditions (psoriasis, acne)
- Drug reactions (acute generalized exanthematous pustulosis)
- Autoimmune disorders
Clinical Pearls
- Pustules that appear in erythema migrans lesions (Lyme disease) are present in approximately 5% of cases 2
- Vesicular-appearing erythema migrans lesions with pustules are not typically associated with significant pruritus, unlike contact dermatitis 2
- In generalized pustular psoriasis, pustules are typically sterile despite their size and appearance 3
The 5 mm threshold serves as an important clinical marker for distinguishing between routine pustular eruptions and those that may indicate more severe disease processes requiring specific therapeutic interventions.