Does not involve a preformed antibody -> requires development of antibody via adaptive immune system
Drug (as a hapten) binds to a plasma protein
Time Required for Primary Sensitization to an Offending Agent: 1-3 wks (however, symptoms may develop within 12-36 hrs, if there has been a prior immunizing exposure)
Role of Circulating Immune Complexes: clinical disease correlates with high levels of circulating immune complexes and decreased C3/C4/CH50 complement components
Diagnosis
125I-Labeled C1q Binding Assay: detects high levels of circulating immune complexes
C3/C4/CH50: markedly decreased
Direct Immunofluorescence of Skin Bx: imunoglobulin + C3 deposits in walls of small cutaneous blood vessels
Clinical Manifestations
Dermatologic Manifestations
Serpiginous Erthematous Band Along Sides of Hands/Feet/Fingers/Toes (at junction of palmar and plantar skin surfaces): early clinical sign
Rash (see Urticaria-Angioedema): mobilliform (maculo-papular, measles-like) and/or urticarial