Primary localised amyloidosis of the orbit.

AIMS/BACKGROUND Primary localised amyloidosis is rarely encountered in the orbit. The typical clinical and radiological appearances have not been clearly established, in particular the single site deposition of amyloid has never been proved. METHODS Six cases were reviewed in detail and their clinical and radiological characteristics are described here. Four patients had scintigraphy with 123I serum amyloid P component and one patient had typing of the amyloid fibrils. RESULTS All the patients had a firm mass in the upper orbit with a predilection for the region of the lacrimal gland. Computed tomography showed a homogeneous mass with thickening and irregularity of the adjacent bone and/or calcification within the mass. None was associated with systemic disease. Scintigraphy with 123I serum amyloid P component demonstrated that the amyloid was confined to the orbit. In one patient the amyloid fibrils were derived from an IgG4 heavy chain constant domain. The lesions were partially excised with subsequent clinical stability over 6 months to 18 years in all but one patient who had continued enlargement of the lesion. CONCLUSION There is a characteristic clinical and radiological pattern for primary localised amyloidosis of the orbit. The disease process is truly local and not part of a systemic process. A majority respond to simple debulking with subsequent observation.