A 21-year-old woman comes to the emergency department due to a worsening skin rash. The patient returned from a 3-day camping and hiking trip in the Colorado mountains and developed an itchy, erythematous rash on her upper extremities and torso later that day. Some of the lesions progressed into small blisters. She reports falling into a bush and getting a few insect bites during the trip. Medical history includes seizures managed with levetiracetam. The patient is menstruating. Temperature is 37.2 C (99 F), blood pressure is 116/68 mm Hg, and pulse is 90/min. On physical examination, the patient appears to be uncomfortable. Skin examination findings are shown in the exhibit. No oropharyngeal lesions are present. The lungs are clear to auscultation, and heart sounds are normal. The abdomen is soft and nontender. Which of the following is the most likely cause of this patient's current condition?

Question

A 21-year-old woman comes to the emergency department due to a worsening skin rash.  The patient returned from a 3-day camping and hiking trip in the Colorado mountains and developed an itchy, erythematous rash on her upper extremities and torso later that day.  Some of the lesions progressed into small blisters.  She reports falling into a bush and getting a few insect bites during the trip.  Medical history includes seizures managed with levetiracetam.  The patient is menstruating.  Temperature is 37.2 C (99 F), blood pressure is 116/68 mm Hg, and pulse is 90/min.  On physical examination, the patient appears to be uncomfortable.  Skin examination findings are shown in the exhibit.  No oropharyngeal lesions are present.  The lungs are clear to auscultation, and heart sounds are normal.  The abdomen is soft and nontender.  Which of the following is the most likely cause of this patient's current condition?

Quizplus · Accepted Answer

Explanation: 11ec25c8_d374_d92a_bc81_711485eb1485_MD0003_00 This patient has acute allergic contact dermatitis (ACD), likely due to exposure to Rhus plants (eg, poison ivy). ACD can also be triggered by natural rubber, leather dyes, nickel, topical medications, skin care products, and other allergens. ACD is a type IV (delayed-type) hypersensitivity reaction that occurs in 2 phases. In the sensitization phase, naive T cells in the regional lymph nodes develop into allergen-sensitive T cells after initial exposure; this phase does not result in cutaneous lesions. On reexposure (elicitation phase), previously sensitized (memory) T cells proliferate and release inflammatory cytokines that promote cell-mediated cytotoxicity (CD8⁺ T cells) and macrophage recruitment and activation. The resulting tissue effects are typically evident within 48-72 hours. Lesion morphology depends on the severity and chronicity of the exposure. Mild, acute cases manifest as erythematous, indurated plaques; in severe cases, vesiculation and bullae may appear, as in this patient. In contrast, chronic, low-level exposure to an allergen (eg, nickel clothing fasteners) leads to scaling, lichenification, and fissuring. Itching is a dominant feature in all cases. Treatment includes allergen avoidance and topical or systemic corticosteroids. lichenification (Choice B) Bullous pemphigoid is an autoimmune blistering disease characterized by tense bullae and plaques. Although it can have a variable prodrome of pruritic lesions resembling ACD, it is most common at age >60, and symptoms typically occur chronically over weeks to months, rather than acutely. bullae (Choice C) Staphylococcal toxic shock syndrome (TSS) is due to absorption of toxic shock syndrome toxin-1, typically related to retained foreign material (eg, high-absorbency tampon). Unlike ACD, TSS presents with high fever, hypotension, and multisystem involvement (eg, diarrhea), in addition to a macular rash resembling a sunburn. Vesicles and bullae are not characteristic. (Choice D) Drug-induced keratinocyte necrosis indicates Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN). Although many antiepileptics (eg, levetiracetam) can cause SJS/TEN, the rash is characterized by skin/mucosal pain (not pruritus) with epidermal necrosis and sloughing. It is typically preceded by fever and flu-like symptoms. Keratinocyte necrosis is also seen with contact dermatitis, but it is not drug-induced in this patient. epidermal necrosis and sloughing (Choice E) Rickettsia rickettsii causes Rocky Mountain spotted fever and is transmitted via tick bites. The associated rash is maculopapular or petechial, not vesicular, and originates at the wrist and ankles. Fever, myalgias, and headache are usually present. petechial Educational objective: Allergic contact dermatitis is a delayed-type hypersensitivity reaction caused by activation of memory T cells. The acute rash is characterized by intense pruritus, erythema, edema, and vesicles/bullae. References: Diagnosis and management of contact dermatitis. (http://www.ncbi.nlm.nih.gov/pubmed/20672788)

A 21-Year-Old Woman Comes to the Emergency Department Due to a Worsening