Introduction And Definitions
- Blister defined as circumscribed elevated superficial fluid-filled cavity,.
- Vesicle measures < 0.5 cm in diameter,.
- Bulla measures > 0.5 cm in diameter,.
- Intraepidermal blisters generally thin-walled, flaccid, easily ruptured.
- Subepidermal blisters generally tense, thick-walled, highly durable.
Congenital And Mechanobullous Disorders
Sucking Blisters
- Present strictly at birth.
- Located on upper limbs including radial forearm, thumb, and index finger.
- Induced directly by vigorous in utero sucking.
- Resolves rapidly without permanent sequelae.
- Requires no therapeutic intervention.
Epidermolysis Bullosa
- Heterogeneous genetic disorders featuring extreme skin fragility.
- Blistering universally induced by trivial mechanical trauma.
- Exacerbated frequently in warm environmental temperatures.
| Variant | Cleavage Plane | Targeted Protein Defect | Clinical Features And Management |
|---|
| Epidermolysis Bullosa Simplex | Intraepidermal | Keratin 5 or Keratin 14. | Heals without scarring,. Management includes friction avoidance, blister puncture leaving roof intact, infection monitoring. |
| Junctional Epidermolysis Bullosa | Subepidermal (Lamina lucida) | Laminin 332 or Type XVII collagen. | Rampant dental caries, perioral granulation tissue, severe mucosal involvement. High mortality secondary to septicemia and cachexia. |
| Dystrophic Epidermolysis Bullosa | Subepidermal (Sublamina densa) | Type VII collagen. | Severe scarring, extensive milia formation, mitten-hand pseudosyndactyly,. High risk for cutaneous squamous cell carcinomas. |
Infectious Bullous Dermatoses
Bullous Impetigo
- Primary infection of infants and young children.
- Caused universally by Staphylococcus aureus.
- Epidermolytic toxins (ETA, ETB, ETD) cleave human desmoglein 1.
- Produces subcorneal vesicle.
- Flaccid, transparent bullae erupt on intact skin.
- Rupture leaves narrow scale rim surrounding shallow moist erosion.
Staphylococcal Scalded Skin Syndrome
- Mediated by hematogenous dissemination of epidermolytic toxins A or B.
- Triggered by phage group 2 staphylococci (strains 71 and 55) from distant infectious focus.
- Cleavage occurs subcorneally via desmoglein 1 targeting.
- Intact bullae remain consistently sterile.
- Scarlatiniform erythema progresses to widespread flaccid blisters and superficial peeling.
- Positive Nikolsky sign universally present.
- Intraoral mucosal surfaces characteristically spared.
- Management mandates hospitalization, meticulous fluid and electrolyte monitoring, and parenteral antistaphylococcal antibiotics (nafcillin, cefazolin, clindamycin, or vancomycin).
Autoimmune Blistering Disorders
| Disorder | Pathophysiology | Clinical Manifestations |
|---|
| Pemphigus Vulgaris | Autoantibodies against desmoglein III producing suprabasal cleavage. | Painful oral ulcers frequently present initially. Large flaccid bullae on non-erythematous skin. Positive Nikolsky sign. |
| Bullous Pemphigoid | Autoantibodies against 180-kDa (type XVII collagen) or 230-kDa basement membrane proteins. Subepidermal split. | Tense bullae arising on normal, erythematous, or urticarial base. Predilection for flexural extremity aspects, axillae, groin. |
| Linear Immunoglobulin A Dermatosis | Immunoglobulin A mediated dermoepidermal split. | Target preschool age. Tense, clustered bullae arranging in rosette-like “string of pearls” pattern. Predilection for genitals, buttocks, perioral areas. |
Hypersensitivity Reactions
Stevens-Johnson Syndrome And Toxic Epidermal Necrolysis
- Represents continuous clinical spectrum.
- Stevens-Johnson Syndrome involves < 10% body surface area.
- Toxic Epidermal Necrolysis involves > 30% body surface area.
- Precipitated primarily by sulfonamides, nonsteroidal anti-inflammatory agents, and anticonvulsants.
- Pathogenesis involves drug-specific CD8+ cytotoxic T cells triggering keratinocyte apoptosis via perforin/granzyme B and granulysin.
- Erythematous macules develop central necrosis evolving into vesicles and bullae.
- Severe mucosal ulcerations involve two or more anatomical sites (ocular, oral, airway, anogenital),.
- Positive Nikolsky sign documented.
- Therapy mandates immediate drug cessation, intensive fluid and nutritional support, and advanced wound care.
Diagnostic Evaluation By Cleavage Site
- Precise identification guides therapeutic intervention.
| Disorder Entity | Histological Cleavage Site | Primary Diagnostic Modality |
|---|
| Bullous Impetigo | Granular layer. | Bacterial smear and culture. |
| Epidermolysis Bullosa Simplex | Intraepidermal. | Electron microscopy, immunofluorescence mapping. |
| Junctional Epidermolysis Bullosa | Subepidermal. | Electron microscopy, immunofluorescence mapping. |
| Pemphigus Vulgaris | Suprabasal (Intraepidermal). | Direct immunofluorescence demonstrating “chicken wire” pattern. |
| Erythema Multiforme | Subepidermal. | Routine histopathology. |
