Dermatitis Types and Pathology

Acute Eczematous Dermatitis

• Type 4 hypersensitivity reaction: T-cell mediated, meaning the immune system's T cells are involved.
• Causes:
  • Allergic contact dermatitis: Antigen (allergen) is presented to naïve CD4 T cells by Langerhans cells (DCs), leading to sensitization and effector/memory T cell formation; re-exposure triggers cytokine release from memory T cells.
  • Drug-related: Some medications can trigger this type of dermatitis.
  • Photoeczematous: Reaction to light and certain plant chemicals.
  • Primary irritant: Caused by loss of function in the filaggrin protein, leading to a type 4 hypersensitivity response.

Atopic Dermatitis

• More severe and common in darker skin tones.
• Typically located in areas of flexion: Such as the cubital fossa (elbow) and popliteal fossa (behind the knee).

Histopathology

• Spongiosis: Fluid accumulation in the epidermis, giving it a spongy appearance.

Complications

• Pruritus: Intense itching.
• Blisters: Can form and eventually crust over.

Clinical Features

• Redness (erythema).
• Dry skin.
• Itching.
• Scaly skin.

Management

• Corticosteroids: Used to reduce inflammation and itching.

Types of Eczema

• Atopic eczema: A chronic, inflammatory skin condition.
• Contact eczema: Triggered by an allergic reaction to a specific substance.

Urticaria (Hives)

• Chronic autoimmune disorder with a type 1 hypersensitivity reaction
• IGE mediated mast cell degranulation causes microvascular hyperpermeability
• Characterized by raised, itchy (pruritic), red plaques called wheals

Urticaria (Hives)

• An autoimmune disorder
• A type 1 hypersensitivity reaction
• Mediated by IgE and mast cells
• Leads to microvascular hyperpermeability
• Characterized by raised, itchy, red plaques called wheals

Erythema Multiforme Pathophysiology

• Characterized by hypersensitivity reaction, often triggered by medications or infections like herpes simplex virus (HSV)
• Immune response involves IgM deposition and inflammatory cell infiltration at the dermis-epidermis junction (interface dermatitis)
• Individual keratinocytes undergo apoptosis, leading to basal keratinocyte degeneration
• Spongiosis, a characteristic of this condition, involves intercellular edema within the epidermis
• Notably, necrosis is absent in typical Erythema Multiforme cases, but may occur in complications

Clinical Features

• Distinctive target or iris-like lesions are a hallmark of Erythema Multiforme
• Positive Nikolsky sign, where the epidermis detaches with minimal pressure, indicates a complication

Complications

• Stevens-Johnson Syndrome: Severe, potentially life-threatening complication involving extensive skin blistering and ulceration
• Toxic Epidermal Necrolysis (TEN): Extreme form with widespread epidermal detachment and high mortality rates
• Widespread Skin Ulceration: Characterized by extensive open sores on the skin
• Epidermal Necrolysis: Necrosis of the epidermis, often leading to shedding of the skin
• Fever-Like Symptoms: Common in Erythema Multiforme, characteristic of a type 4 hypersensitivity reaction