Systemic kappa light-chain deposition. An ultrastructural and immunohistochemical study.

This report describes the pathology of kappa light-chain deposition in a 55-year-old patient who presented with respiratory insufficiency and hepatomegaly. Biopsies of lung and liver showed PAS-positive deposits which did not stain with congo red, crystal violet, or thioflavin-T. By indirect immunoperoxidase techniques, the deposits were composed of kappa light-chain immunoglobin. Electron microscopy revealed granular and fibrillar electron-dense material which lacked the characteristics of amyloid. Subsequent clinical studies showed this patient had a plasma cell dyscrasia. These data show that kappa light-chain deposition is not limited to the kidney, and that the first manifestation of a plasma cell dyscrasia may be systemic deposits of light chain. These deposits can be distinguished from amyloid by their immunochemical, tinctorial, and ultrastructural appearance.