Allergic contact dermatitis - Cellulitis
Contact dermatitis presents as either allergic or irritant in etiology. While irritant contact dermatitis represents the direct toxic effect of an offending agent on the skin, allergic contact dermatitis (ACD) represents a delayed-type (type IV) hypersensitivity reaction that occurs when allergens activate antigen-specific T cells in a sensitized individual. Consequently, whereas irritant contact dermatitis can occur after one exposure to the offending agent, ACD typically requires repeat exposures before an allergic response is noted. ACD can occur 24-48 hours after exposure to the offending agent.
Contact dermatitis can demonstrate well-demarcated borders, suggestive of an "outside job" or external contact. It can also present as a systemic contact reaction with widespread lesions when the offending agent is ingested or present in an implanted device. ACD can occur in reaction to topical agents, ingested agents, implanted biomedical devices, and airborne materials.
The intense erythema and sharply demarcated plaques of contact dermatitis are easy to confuse with cellulitis or erysipelas, especially when vesiculation and bullae formation take place. Differentiating features include the presence of pruritus (often extreme) in contact dermatitis versus the skin warmth and spreading erythema of a soft tissue infection. A detailed allergen exposure history should be elicited.
L23.9 – Allergic contact dermatitis, unspecified cause
40275004 – Contact dermatitis
- Stasis dermatitis
- Cellulitis – Plaque margins in cellulitis are often less distinct than those of contact dermatitis. The plaques of contact dermatitis are sharply demarcated and frequently take on bizarre geometric shapes and patterns.
- Atopic dermatitis
- Irritant contact dermatitis
- Nummular dermatitis (nummular eczema)
- Insect bite reaction
- Tinea corporis
- Lichen simplex chronicus
- Cutaneous T-cell lymphoma / mycosis fungoides – If an adult patient has persistent "eczema" that is not adequately responding to therapy, this entity should be ruled out with skin biopsies.
- Herpes simplex virus infection
- Sweet syndrome
- Necrobiosis lipoidica
- Erythema nodosum
- Pretibial myxedema
- Fixed drug eruption
- Eosinophilic cellulitis
- Lyme disease
Last Updated: 02/14/2018