Case 1 History
The patient is a 22-year-old female who reports the rapid onset of widespread, pruritic, edematous papules surrounded by erythema. There is no surface change. Resolution occurs within a few hours. She reports similar symptoms 1 year ago that also showed the same rapidly remitting time course.
Microscopic Findings
Sections show scattered perivascular and interstitial lymphocytic inflammation involving the superficial dermis. There are also scattered interstitial eosinophils and neutrophils. There is increased separation of collagen bundles, suggesting edema ( Fig. 7.1 ).
Diagnosis
Urticaria
Clinical Presentation
Urticaria presents as pruritic edematous papules and plaques that can be localized or widespread. This is a common, temporary ailment that affects about 15% of the population at some point in their lives. Resolution occurs within hours. The underlying cause is often unknown (idiopathic), but there can be associations with autoimmunity or specific triggering stimuli, such as physical effects (cold or pressure), medications, or a recent infection.
Histopathology
The epidermis is uninvolved. In the superficial dermis, sections show a perivascular and interstitial mixed infiltrate with neutrophils and eosinophils. Vessels may be dilated.
Differential Diagnosis
The differential diagnosis includes arthropod assault and drug eruption, and in many instances, distinction based solely on histopathologic grounds is not possible. , Clinicopathologic correlation is required. If the tissue infiltrate shows a predominance of neutrophils, Sweet syndrome becomes an additional consideration ( Table 7.1 ).
| Urticaria | Arthropod Assault | Morbilliform Drug Eruption | Erysipelas | |
|---|---|---|---|---|
| Clinical presentation | Pruritic edematous papules and plaques that last for hours | Pruritic papules, often with secondary excoriation | Erythematous maculopapular eruption, often widespread | Painful delineated plaques, often unilateral, with fever |
| Epidermal changes | None | Focal epidermal necrosis if excoriated | Mild vacuolar change | Nonspecific |
| Composition of dermal infiltrate | Lymphocytes, eosinophils, and neutrophils | Lymphocytes, eosinophils, and neutrophils | Lymphocytes and eosinophils | Neutrophils, lymphocytes, and few eosinophils |
| Location of dermal infiltrate | Superficial | Superficial and deep | Mostly superficial | Superficial and deep |
| Distinct histopathologic features | None | Chitin, if present | None | Bacteria, if present |
Arthropod Assault
Clinical Presentation
Dermatitis induced by the bite or sting of an arthropod often presents as grouped erythematous pruritic macules and papules. There may be associated overlying secondary changes stemming from excoriation in reaction to pruritus.
Histopathology
The prototypical pattern is that of a wedge-shaped perivascular and interstitial infiltrate composed of lymphocytes, histiocytes, and many eosinophils involving the superficial and deep dermis ( Fig. 7.2 ). The spacing of collagen bundles is widened because of the presence of interstitial edema. There is often some degree of overlying nonspecific epidermal change or disruption. Neutrophils may predominate in some reactions. There can be marked papillary dermal edema, creating a bulla-like configuration. Occasionally, thrombotic occlusion of a dermal vessel is found.
Whereas an arthropod reaction tends to be superficial and deep in distribution with a dense infiltrate, the infiltrate of urticaria tends to be superficial and sparse. However, there is significant overlap.
Morbilliform Drug Eruption
Morbilliform drug eruptions represent a common cutaneous medication reaction. Triggering agents include antibiotics, phenytoin, benzodiazepines, and a variety of other drugs. Clinical correlation is an important component of the diagnosis.
Clinical Presentation
A drug reaction presents as symmetric, widespread, brightly erythematous maculopapular rash that involves the trunk and extremities. The eruption often occurs within a few weeks after the initiation of drug therapy. Occasionally, a longstanding agent will trigger a reaction.
Histopathology
The dominant histopathologic pattern consists of a superficial perivascular lymphocytic infiltrate with scattered eosinophils. There is often associated dermal edema. Epidermal change is often present, but the change may be subtle. Either slight spongiosis or subtle vacuolar change is typical.
Erysipelas
Erysipelas is an acute bacterial infection, typically triggered by β-hemolytic streptococci, with a clinical presentation distinct from urticaria.
Clinical Presentation
Patients develop painful sharply delineated red patches or plaques, often accompanied by fever and lymphadenopathy. Unilateral facial involvement is typical.
Histopathology
Histopathology reveals a perivascular and interstitial infiltrate of neutrophils, lymphocytes, and occasional eosinophils ( Fig. 7.3 ).There may be associated edema or purpura. The histopathologic pattern is not specific.
