bullae
Summary
A bulla is a fluid-filled blister larger than 1 cm in diameter; smaller lesions are vesicles. In the lung the same word describes an air-filled space greater than 1 cm produced by destruction of alveolar walls in emphysema.
Detail
In dermatology the level of blister formation determines the disease and its severity. Subepidermal bullae, as in bullous pemphigoid (IgG against hemidesmosomal BP180/BP230) and dermatitis herpetiformis, are tense and Nikolsky sign negative because the full-thickness epidermal roof is intact. Intraepidermal bullae, as in pemphigus vulgaris (IgG against desmoglein 1 and 3) and staphylococcal scalded skin syndrome (exfoliative toxin cleaving desmoglein 1), are flaccid, rupture easily, and are Nikolsky sign positive. Other causes include bullous impetigo, burns, fixed drug eruption, porphyria cutanea tarda, and Stevens-Johnson syndrome/toxic epidermal necrolysis. In pulmonary usage, bullae are the end result of alveolar wall destruction in emphysema; rupture of a subpleural apical bleb or bulla is the mechanism of primary spontaneous pneumothorax in tall thin young men and in alpha-1 antitrypsin deficiency.
Sources
- First Aid for the USMLE Step 1
- Robbins Basic Pathology
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