Spondylosis in sand rats: a model of intervertebral disc degeneration and hyperostosis

This study defines gross, histopathologic, and radiologic changes associated with intervertebral disc degeneration in a spontaneously occurring form of the disease in aging sand rats (Psammomys obesus). Sand rats (male/female) fed lab chow supplemented with desert salt bush were sacrificed at periods of 3-30 months. Lateral thoracolumbar spine films were obtained. At sacrifice, spines were surgically exposed and gross findings were recorded; after fixation/decalcification, histopathologic studies were carried out using hematoxylin and eosin, and Safranin-O with fast green counterstain. Metabolic studies included correlations of pathologic and radiologic findings with blood glucose and insulin levels. Disc-space narrowing and subchondral endplate sclerosis increased radiologically with age, with more severe lower lumbar disc lesions. Ligamentous calcifications ventral to involved discs and caudal vertebrae were common. Disc thinning and anterior vertebral bony/cartilaginous spurs were more marked with age. Microscopy revealed loss of nucleus pulposus physaliform cells, chondrocyte replication, disc necrosis, and ossification. Hyperglycemia with and without hyperinsulinemia was common. No statistically significant differences in pathologic findings were noted, neither in diabetic versus nondiabetic nor in hyperinsulinemic animals. The sand rat is a model of disc degeneration; similarities with possible overlap with diffuse idiopathic skeletal hyperostosis syndrome were noted.