Kappa III immunoglobulin light chain origin of localized orbital amyloidosis.

Isolated orbital amyloidosis is a rare condition in which intra-muscular deposits result in proptosis and restriction of eye movement. Previous reports have suggested an immunoglobulin origin of the amyloid fibrils, but this has not been proven biochemically. A case is presented in which initial unilateral orbital amyloidosis progressed to bilateral disease. Biochemical analysis of resected ocular muscle determined that the amyloid fibrils were derived from a kappa III immunoglobulin light chain. Questions of pathogenesis and tissue tropism are considered.