ABSTRACT
Localized orbital amyloidosis is a rare but well recognized entity in which fibril proteins are deposited within the extraocular muscles or adnexae. Orbital amyloidosis usually presents as unilateral proptosis with restricted eye movement but occasional bilateral involvement has been reported. Affected individuals seek medical attention because of diplopia or exophthalmos. Analysis of fibrils isolated from the lateral rectus muscle showed that the amyloid protein was derived from a monoclonal kappa light chain whose variable region is most homologous to the kappa III subgroup. These results demonstrate that isolated orbital amyloidosis is a monoclonal plasma cell disease. The amyloid process is progressive and may be bilateral. The possibility of chronic inflammatory reaction with subsequent local proliferation of a plasma cell clone is raised.
