Scabietic nodules: a dermatopathologic and immunofluorescent study

Mites and their eggs were thought to be rarely found in nodular lesions of scabies. However, serial sections from 27 scabietic scrotal papules or nodules revealed mite parts in 22% (6/27). This supports the contention that scabietic nodules may result from persisting antigens of mite parts. In contrast to previous studies, vasculitis with fibrinoid degeneration was uncommon (3/27) in our series. This discrepancy may be due to the timing of the biopsies: 2 of 3 cases with vasculitis were associated with diffuse dense infiltration, and vasculitis may be a late event in the development of scabietic nodules. The specificity of immunoreactant deposits along the epidermodermal junction (EDJ) in scabies is controversial. In our study, direct immunofluorescence (DIF) was performed on 13 scabietic nodules. Four (31%) showed immunoreactants at the EDJ and two on blood vessels. Because of the relatively low positive rate, the low intensity of fluorescence, and 3 of 4 cases with positive immunoreactants having only a single class of immunoglobulin, the deposition may only be secondary to inflammation instead of a specific type II immunologic reaction to scabies.