A 26-year-old man returns to the emergency department after developing a fever and skin rash. The patient was discharged from the hospital 10 days ago after treatment for a copperhead snake bite to his left leg. He received multiple doses of polyvalent Fab antivenom therapy and other supportive care during hospitalization. The patient's bite site pain, swelling, and ecchymosis have resolved; however, he has developed fever, pain in multiple extremity joints, and pruritic rash over the past 2 days. He has no chronic medical conditions. Temperature is 38.5 C (101.3 F), blood pressure is 128/70 mm Hg, pulse is 98/min, and respirations are 17/min. Physical examination shows a diffuse urticarial rash. No mucous membrane lesions are present. There is tenderness to palpation of the bilateral metacarpophalangeal joints, wrists, and ankles with no redness or swelling. Blood cell counts, serum chemistry studies, and coagulation parameters are within normal limits. Which of the following is the most likely underlying mechanism of this patient's current condition?

Question

A 26-year-old man returns to the emergency department after developing a fever and skin rash.  The patient was discharged from the hospital 10 days ago after treatment for a copperhead snake bite to his left leg.  He received multiple doses of polyvalent Fab antivenom therapy and other supportive care during hospitalization.  The patient's bite site pain, swelling, and ecchymosis have resolved; however, he has developed fever, pain in multiple extremity joints, and pruritic rash over the past 2 days.  He has no chronic medical conditions.  Temperature is 38.5 C (101.3 F), blood pressure is 128/70 mm Hg, pulse is 98/min, and respirations are 17/min.  Physical examination shows a diffuse urticarial rash.  No mucous membrane lesions are present.  There is tenderness to palpation of the bilateral metacarpophalangeal joints, wrists, and ankles with no redness or swelling.  Blood cell counts, serum chemistry studies, and coagulation parameters are within normal limits.  Which of the following is the most likely underlying mechanism of this patient's current condition?

Quizplus · Accepted Answer

Eductional Objective: Serum sickness is an immune complex-mediated type III hypersensitivity reaction that occurs 1-2 weeks after exposure to nonhuman protein in antitoxins (eg, antivenom), monoclonal antibodies (eg, rituximab), or vaccines (eg, rabies antigens).  Deposition of immune complexes in tissue leads to complement activation and subsequent self-limited fever, arthralgia, and urticarial rash.

A 26-Year-Old Man Returns to the Emergency Department After Developing