Nylon brush macular amyloidosis.

Long-term use of a nylon brush for back scratching by a 53-year-old white woman was associated with the development of typical macular amyloidosis. EKH4 monoclonal antikeratin antibody, which recognizes 50-kd neutral and acidic keratin species, labeled this amyloid. Confirmation of amyloid substance in the lesion included positive staining with Dylon and thioflavin T; immunohistochemical reactions with monoclonal and polyclonal antibodies against elastic fiber microfibrils (NKH1 and anti-P component), immunoglobulins (IgG, IgM, and IgA), and complement (C3); and electron microscopic identification of 6- to 10-nm straight filaments. Type IV collagen staining demonstrated a breakage and/or thickening of the dermoepidermal basement membrane above the amyloid deposition in the papillary dermis. Electron microscopic findings confirmed this phenomenon.