A histopathological correlation of Bruch’s membrane calcification in pseudoxanthoma elasticum with clinical retinal imaging

Abstract

Purpose : To investigate the histology of Bruch’s membrane calcification in pseudoxanthoma elasticum (PXE) and correlate this to clinical retinal imaging.

Methods : Six post-mortem eyes from four PXE patients and one age-matched control were investigated. Eyes were stained with Osteosense 680RD, a fluorescent dye specific for apatite. Labelling was visualized with a confocal microscope with an excitation wavelength of 620nm and an emission wavelength of 680nm. Scanning electron microscopy coupled with energy-dispersive x-ray spectroscopy (SEM-EDX) and time of flight-secondary ion mass spectrometry (TOF-SIMs) were used to analyze the elemental and ionic composition at specific anatomical locations. The findings of one PXE patient were compared with prior clinical retinal imaging.

Results : All whole-mounted PXE eyes revealed extensive Osteosense labelling in the central retina, changing to a patchy but intensively labelled fiber-like structure at the area of the clinical manifestations of orange peel. Calcification also occurs in the age-matched control eye without PXE, but this mineralization appeared as small "snowflake-like" depositions more numerous around the optic nerve. Whole-eye cross-sections of all PXE eyes revealed confluent mineralization on confocal microscopy. Still, it is the complete mineralization of fibres in the Bruch's membrane, transitioning to speckled staining in the mid-periphery, again, corresponding to the transition zone on clinical imaging. SEM-EDX and TOF-SIMs analyses confirmed the presence of hydroxyapatite throughout the Bruch’s membrane.

Conclusions : PXE eyes show extensive and confluent hydroxyapatite deposition in the central Bruch’s membrane with a gradual change in the distribution of calcification to the mid-periphery, which likely corresponds with the clinical phenotype. The snowflake-like calcification deposits in Bruch’s membrane of a healthy aged eye differed markedly from the extensive calcification in PXE.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.