| • | type III hypersensitivity reaction (immune complexes) |
classically:
| • | morbilliform, with or without urticaria |
| • | fever, malaise, arthralgias, arthritis |
| • | in true serum sickness, C3 and C4 levels decreased |
| • | most often associated with exposure to foreign proteins (ex. immune globulin, human diploid cell rabies vaccine) |
| • | typically 1-2 weeks after first exposure |
ddx:
| • | hypersensitivity syndrome (DRESS) |
| • | acute viral and drug induced serum sickness-like illness |
Serum Sickness-Like Reactions
| • | clinically similar: rash, fever, arthralgias or myalgias |
| • | but almost certainly the result of different mechanisms |
| • | in contrast to true serum sickness: immune complexes, hypocomplementemia, vasculitis and renal lesions are uncommon |
| • | culprits: cephalosporins (esp. cefaclor), PCN’s, sulfonamides, minocylcine, hepatitis B |
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