Spheroidal Keratopathy Associated with Subepithelial Corneal Amyloidosis: A Clinicopathologic Case Report and a Proposed New Classification for Spheroidal Keratopathy

Abstract

An unusual case of primary spheroidal degeneration associated with subepithelial corneal amyloidosis is described clinically and histopathologically, and a new classification for spheroidal keratopathy is proposed. The corneal button obtained by lamellar keratoplasty was examined by light and transmission electron microscopy. Amyloid deposits were evaluated further by means of the thioflavin T fluorescence technique, the potassium permanganate reaction, and immunohistochemical studies using antibodies against immunoglobulin light chains and proteins AA and AP. Spheroidal droplets were observed in basement membrane, Bowman's layer, and anterior stroma, and exhibited characteristic staining with Verhoeff's iron hematoxylin. Amyloid deposits were found beneath the epithelium, almost exclusively in the central area of the corneal button. The deposits showed no immunohistochemical staining with antibodies to amyloid proteins AA and AP or kappa and lambda light chains. The histochemical properties of the spheroidal droplets in this case were similar to those observed by other authors and suggested a sulfur-rich protein other than keratin. The combination of clinical and pathologic findings permitted the differential diagnosis of subepithelial amyloidosis and distinguished this condition from that of gelatinous drop-like dystrophy. To the authors' knowledge, this is the first description of primary spheroidal keratopathy associated with secondary subepithelial corneal amyloidosis in an eye that had not undergone previous keratoplasty.