Pathophysiology of Dyshidrotic Eczema
Dyshidrotic eczema is an inflammatory skin disorder characterized by eczematous reactions around sweat ducts, though paradoxically, the sweat ducts themselves show no structural abnormalities—the exact pathophysiology remains incompletely understood but involves a complex interplay of immune dysregulation, barrier dysfunction, and potential hypersensitivity mechanisms. 1
Core Pathophysiologic Mechanisms
Inflammatory Response Pattern
The histopathologic findings reveal a characteristic eczematous reaction pattern with:
- Spongiosis (intercellular edema in the epidermis)
- Development of intraepidermal vesicles 2
- Perivascular lymphohistiocytic infiltrates
- Keratinocyte abnormalities including necrosis
- Interface dermatitis with variable capillary dilation 3
These findings are consistent with toxic dermatitis patterns, though the molecular and cellular mechanisms driving this response remain poorly understood 3.
Immune Dysregulation
The immune component involves:
- Activation of CD4+ T lymphocytes, indicating intensity of inflammatory response 2
- Complement system activation with C3 and C4d deposition, particularly in treatment-resistant cases 2
- Proinflammatory cytokine release from keratinocytes leading to skin barrier disruption and cellular changes 4
Notably, patients with the 646 CC genotype of the NR3C1 gene (glucocorticoid receptor gene) who are treatment-resistant show more pronounced complement activation compared to treatment-sensitive patients 2.
Skin Barrier Dysfunction
The pathophysiology shares features with atopic dermatitis:
- Epidermal barrier abnormalities that enhance release of thymic stromal lymphopoietin, promoting Th2 cell differentiation 5
- Cross-talk between barrier dysfunction and aberrant immune responses 5
- Acute loss of surface lipids and depletion of stratum corneum lipid barrier 4
- Decreased protective proteins making skin vulnerable to irritation 4
Etiologic Factors Contributing to Pathogenesis
Hyperhidrosis Association: While dyshidrotic eczema often occurs in individuals with hyperhidrosis and the name suggests sweat involvement, the histologic examination shows eczematous reactions around (not in) sweat ducts with no ductal abnormalities 1. This suggests hyperhidrosis may be a trigger rather than a direct cause 6.
Metal Hypersensitivity: Contact sensitization, particularly to metals (nickel and cobalt), represents an important etiologic factor 1, 7. High oral ingestion of these metals can trigger flares regardless of patch test results 7. In occupational studies, 72.8% of dyshidrotic patients showed positive patch test reactions, though the relationship to occupational activity (30.5%) was lower than other hand eczema forms (55%) 8.
Genetic Susceptibility: Polymorphic variants of the NR3C1 gene (particularly C646G) influence both pathomorphological features and treatment response, with the 646 CC genotype associated with enhanced complement activation and treatment resistance 2.
Clinical Pitfalls
- Do not assume sweat duct pathology: Despite the name and association with hyperhidrosis, the sweat ducts are structurally normal 1
- Consider metal allergy even with negative patch tests: Systemic exposure through diet can trigger disease 7
- Recognize atopic overlap: Approximately 42.4% of dyshidrotic eczema patients have atopic history, similar to other hand eczema forms 8
- Understand the itch-scratch cycle: This perpetuates barrier damage and inflammation, creating a self-sustaining pathologic loop 5
The pathophysiology represents a final common pathway where genetic predisposition, immune activation, barrier dysfunction, and environmental triggers (hyperhidrosis, metal exposure, irritants) converge to produce the characteristic vesicular eruption on palmoplantar surfaces 1, 9.