Inflammatory Dermatosis - Pathology Central Key Concepts

Introduction

• Inflammatory Dermatosis: Complex due to immune dysregulation.
• Skin's Role: Interface with outside world, exposed to antigens/pathogens, mounts immune response.
• Objective: Review inflammation patterns in skin and six diseases categorized under three patterns.

Skin Structure

• Layers:
  • Stratum corneum
  • Granular layer
  • Spinous layer
  • Basal layer
  • Superficial dermis

Key Terms

• Hyperkeratosis: Thickening of the stratum corneum, loss of basket weave.
• Perikeratosis: Nuclei retention in thickened stratum corneum.
• Acanthosis: Expansion of spinous layer, epidermal hyperplasia.
• Spongiosis: Edema in epidermis, splaying keratinocytes.

Clinical Presentation

• Acute Onset: Days to weeks, lymphocytes/macrophages, not neutrophils.
• Chronic Inflammation: Months to years, epidermal growth changes, dermal fibrosis.

Patterns of Inflammation

1. Spongiotic Dermatitis: Epidermal edema.
   • Examples: Allergic contact dermatitis, atopic dermatitis.
2. Interface Dermatitis: Inflammatory infiltrate at dermal-epidermal junction.
   • Patterns: Vacuolar degeneration (e.g., erythema multiforme), dense band (e.g., lichen planus).
3. Psoriasis Form Dermatitis: Epidermal hyperplasia.
   • Examples: Psoriasis, lichen simplex chronicus.

Spongiotic Dermatitis

Acute Eczematous Dermatitis

• Common Disorders: Allergic contact dermatitis (e.g., poison ivy), atopic dermatitis.
• Progression: Edema, vesicle formation, chronic lesions.

Types

• Allergic Contact Dermatitis: Type IV hypersensitivity, T-cell mediated.
• Atopic Dermatitis: Defects in epidermal barrier, inherited susceptibility.

Interface Dermatitis

Erythema Multiforme

• Characteristics: Basal cell injury, CD8+ T cells, multiple erythematous lesions.

Lichen Planus

• Skin/Mucosa Disorder: Middle-aged adults, self-limited, CD8+ T cell response.
• Clinical Presentation: Purple, polygonal, planar papules/plaques.

Psoriasis Form Dermatitis

Psoriasis

• Chronic Inflammatory Dermatosis: Autoimmune, T-cell mediated.
• Clinical Features: Plaques, nail changes, increased cardiovascular risk.

Lichen Simplex Chronicus

• Repetitive Trauma: Roughening of skin, similar histologically to psoriasis.

Review Questions

• Recall three patterns of inflammation and associated diseases.
• Describe evolution of acute eczematous dermatitis.
• Differentiate psoriasis from lichen simplex chronicus.