Bullae: Definition, Evaluation, and Management
Definition and Classification
A bulla is a fluid-filled blister measuring greater than 1 cm in diameter, which requires fundamentally different evaluation and management depending on whether it is cutaneous (skin) or pulmonary (lung). 1, 2
Cutaneous Bullae
- Defined as circumscribed fluid collections >1 cm in the skin, classified by anatomic level: subcorneal, intra-epidermal, junctional, or subepidermal 2
- Categories include allergic, autoimmune, infectious, mechanical, and metabolic etiologies 1
- Particularly affect adults age 65 and older across all etiologies 1
Pulmonary Bullae
- Sharply demarcated air-filled spaces in the lung measuring ≥1 cm, defined by a thin wall visible on imaging 3
- More common in usual (non-alpha-1 antitrypsin deficiency) emphysema 3
- Main complications include pneumothorax, infection, and hemorrhage 4
Evaluation of Cutaneous Bullae
Critical Initial Assessment: Rule Out Life-Threatening Causes
Immediately assess for necrotizing fasciitis using these red flags: pain disproportionate to physical findings, violaceous bullae, cutaneous hemorrhage, skin sloughing, skin anesthesia, rapid progression, gas in tissue, fever, tachycardia, or hypotension. 5, 6
- If any red flags present: hospitalize immediately for parenteral antibiotics and emergent surgical consultation 5
- Obtain Gram stain and culture of pus/exudates, plus blood cultures if systemic symptoms present 5
Distinguishing Autoimmune from Infectious Bullae
History and morphology are the primary distinguishing features:
Autoimmune Bullous Pemphigoid Features:
- Tense bullae on erythematous or normal-appearing skin of limbs and trunk in elderly patients 5, 6
- Pruritus preceding blisters by weeks to months 5, 6
- Symmetric distribution on flexural surfaces, inner thighs, and abdomen 6
- Associated with neurological disease (cerebrovascular disease, dementia, Parkinson's, epilepsy) 5
- Minimal mucosal involvement 6
Infectious Bullae Features:
- Pain as prominent symptom 7
- Rapid progression with systemic toxicity 5
- May have grouped vesicles on erythematous base (herpes simplex) 7
Essential Diagnostic Testing for Autoimmune Bullae
Direct immunofluorescence (DIF) from perilesional skin is the single most important diagnostic test, showing linear IgG and/or C3 deposits along the dermoepidermal junction. 6
- Histopathology from early intact bulla shows subepidermal cleft with eosinophilic infiltrate 6
- Serum ELISA for anti-BP180 and anti-BP230 antibodies; anti-BP180 >27 U/mL indicates increased relapse risk 6
- Critical pitfall: Never rely on histopathology alone—always obtain DIF when bullous pemphigoid is suspected 6
Diagnostic Testing for Infectious Bullae
- Open vesicles with sterile needle and collect fluid for viral culture or nucleic acid amplification tests (PCR is gold standard for HSV) 7
- Obtain fungal stain to distinguish true infection from colonization—negative fungal stain definitively rules out active fungal infection 5
- Critical pitfall: Never assume infection based on culture alone without confirmatory staining 5, 6
Management of Cutaneous Bullae
Bullous Pemphigoid Treatment
Superpotent topical corticosteroids (clobetasol propionate) are first-line treatment, providing better disease control with significantly lower mortality compared to systemic corticosteroids. 5
Localized Disease:
- Apply superpotent topical corticosteroids directly to lesions only 5
- Escalate to systemic therapy if no improvement within 3-7 days 5
Generalized Disease:
- Apply clobetasol propionate 20g per day over entire body except face 5
- Increase to 40g per day if disease control not achieved within 1-3 weeks 5
- Assess response after 1-3 weeks; begin tapering after 15 days once disease control achieved 5
- Continue maintenance therapy for 8 months, with total treatment duration of 12 months 5
Alternative for Elderly/Frail Patients:
- Anti-inflammatory antibiotics (doxycycline) with or without nicotinamide may be safer and avoid steroid-related complications 5
Monitoring:
- Every 2 weeks for first 3 months, then monthly for next 3 months 5
- Implement osteoporosis prevention when using systemic corticosteroids 5
Critical warning: Never use oral prednisone >0.75 mg/kg/day in bullous pemphigoid—associated with significant mortality in elderly patients. 5, 6
Infectious Bullae Treatment
- Start empiric antibiotics immediately: clindamycin plus penicillin for group A streptococcal/clostridial infections, or vancomycin plus piperacillin/tazobactam for polymicrobial infections 5
- Reevaluate within 24-48 hours to ensure appropriate response 5
- Consider burn unit admission for extensive skin involvement 5
General Blister Care (All Etiologies)
Decompress intact bullae by piercing at base with sterile needle (bevel facing up), selecting a site where fluid drains by gravity. 3, 5
- Gently cleanse blister with antimicrobial solution before piercing 3
- Apply gentle pressure with sterile gauze to facilitate drainage 3
- Never deroof the blister—leave blister roof in situ to act as biological dressing 3
- Cleanse again with antimicrobial solution after drainage 3
- Large blisters may need larger needle and multiple punctures 3
- Offer analgesia prior to procedure—patients report pain or burning sensation 3
- Apply nonadherent dressing if necessary 3
Post-Drainage Care:
- Apply bland emollient (50% white soft paraffin and 50% liquid paraffin) to support barrier function and encourage re-epithelialization 3
- Daily washing with antibacterial product decreases colonization 3
- Change dressings using aseptic technique 3
- Send bacterial and viral swabs if erosions show clinical signs of infection 3
- Use systemic antibiotics if local or systemic signs of infection present 3
Critical pitfall: Infection and sepsis are significant risks and major causes of mortality—maintain vigilant infection surveillance. 3
Evaluation of Pulmonary Bullae
Imaging Assessment
High-resolution computed tomography (HRCT) is the most sensitive method for detecting and characterizing pulmonary bullae. 3
Plain Chest Radiography:
- Not sensitive for diagnosis but useful for initial assessment 3
- Signs of hyperinflation: depression and flattening of diaphragm (posteroanterior film), increased retrosternal airspace (lateral film) 3
- Bullae appear as irregular radiolucency with absence of vasculature 3
- Recognition is subjective and dependent on radiograph quality 3
CT Scanning:
- Bullae are sharply demarcated by thin wall and measure ≥1 cm 3
- Emphysema characterized by areas of abnormally low attenuation (use window level of -600 to -800 Hounsfield units) 3
- Quantify size and number of bullae accurately 3
- Assess extent of emphysema in nonbullous lung to predict surgical outcome 3
Critical Differential: Giant Bulla vs. Pneumothorax
Carefully distinguish bullae from pneumothorax using history, physical examination, and CT scan to avoid iatrogenic pneumothorax in patients with bullous disease. 4
- Pneumothorax is serious complication in patients with compromised lung function 4
- CT scan is definitive for differentiation 4
Management of Pulmonary Bullae
Indications for Intervention
- Giant bullae causing symptoms or compromising lung function 3
- Infected fluid-filled bullae 8
- Risk of pneumothorax in patients with compromised lung function 4
Treatment Options
Surgical Resection:
- Indicated for symptomatic giant bullae 4
- Knowledge of extent of emphysema in nonbullous lung useful for predicting outcome 3
Percutaneous Drainage:
- For giant fluid-filled bullae: percutaneous placement of 8.5F catheter enables drainage of fluid and air, leading to rapid symptom resolution within 24 hours 8
- Novel management technique for infected fluid-filled bullae 8