Review Question - QID 217297

This patient presenting with an erythematous rash with bullae formation, stinging pain, and suggestive exposure history to an allergen (poison ivy or oak exposure while playing in the woods) most likely has contact dermatitis. This condition is histologically characterized by epidermal intercellular edema, or spongiosis.

Contact dermatitis is an inflammatory skin condition with 2 distinct pathophysiologies. Allergen contact dermatitis causes delayed-type hypersensitivity, where T-cells are initially sensitized to antigens (through cutaneous dendritic cells) and a reaction occurs during re-exposure to the antigen; common allergens include poison ivy and oak. Irritant contact dermatitis is a non-immunological reaction against some stimuli, which leads to inflammatory cytokine release by keratinocytes; common irritants are chemical substances (e.g., acids or soaps). After 2 to 3 days following exposure, patients can develop burning or stinging pain as well as pruritus. Characteristics of the rashes evolve from earlier stages (erythema, edema, vesicles, bullae, etc.) to later ones (scaling and lichenification). Histological analysis is classically marked by spongiosis. Comprehensive exposure history and patch testing are critical for identifying the cause. Once identified, trigger avoidance is important for avoiding reoccurrence. Acute management includes antihistamines for pruritus control. For inflammation reduction, oral corticosteroids are used for extensive skin involvement (>20%); topical is sufficient for milder situations.

Figure A displays an erythematous rash with multiple bullae and blisters.

Novak-Bilic et al. review histological characteristics of contact dermatitis. While spongiosis is associated with contact dermatitis generally, there are more specific histological findings for irritant vs allergic contact dermatitis. The former is characterized by greater neutrophilic infiltration while the latter is predominated by mononuclear infiltration. Additionally, the number of CD4+ Langerhans cells is increased and decreased in allergic and irritant contact dermatitis, respectively. However, despite these differences, there are no clear biomarkers that separate these types.

Incorrect Answer:
Answer 1: Epidermal acantholysis is a histological finding of pemphigoid vulgaris. It is a serious autoimmune disease characterized by mucocutaneous lesions. Pemphigoid vulgaris is caused by IgG autoantibodies against desmoglein, which plays a role in keratinocyte adhesion. The resulting epidermis separation leads to severe ulcers, blisters, and bullae. It is associated with a positive Nikolsky sign, which is blister formation/extension with pressure or traction against the skin. This patient has a significantly more mild presentation and does not have systemic mucocutaneous involvement.

Answer 3: Full-thickness epidermal necrosis is the histological finding of Steven-Johnson syndrome (SJS) and toxic epidermal necrosis (TEN). Often triggered by medications, both SJS and TEN are characterized by severe reactions of the skin (e.g., bullae, erosions, and denudation), fever, malaise, and myalgia. The condition is known either as SJS or TEN when <10% or >30% of body surface area is involved, respectively. The pathophysiology is thought to be T-cell mediated. This patient did not have any systemic symptoms and there were no signs of erosions or more severe reactions.

Answer 4: Leukocytoclastic vasculitis is a histological finding of IgA vasculitis. As known as Henoch-Schönlein purpura, it is a small vessel vasculitis caused by the deposition of IgA immune complexes in small blood vessels. IgA vasculitis often follows an upper respiratory infection and classically presents with palpable purpura of the lower extremities, abdominal pain, and arthralgias. Most patient can recover spontaneously without treatment, but a serious long-term complication is chronic kidney disease. The patient did not have any palpable purpura or non-dermatological findings.

Answer 5: Subepidermal blisters with eosinophilic infiltration are a histological finding of bullous pemphigoid. Bullous pemphigoid is an autoimmune disease marked by bullae and pruritus. It is caused by IgG autoantibodies against hemidesmosomes located in the epidermal-dermal junction. While it can appear similar to pemphigoid vulgaris, bullous pemphigoid does not involve the mucosa, is generally less severe, and has a negative Nikolsky sign.

Bullet Summary:
Epidermal intercellular edema is a classical histological finding of contact dermatitis.