Suspensory ligament degeneration associated with pituitary pars intermedia dysfunction in horses

In older horses, pituitary pars intermedia dysfunction (PPID) and suspensory ligament (SL) degeneration are common. The aim of the present study was to identify histopathological changes in the SL in horses with PPID. SLs of four horses with clinical signs of PPID (17-26 years of age) were compared with SLs from four old horses (18-31 years of age) and three young horses (4-9 years of age). In horses with PPID, there was reduced longitudinal arrangement of collagen fibres in SLs, along with inclusions of cartilage, extracellular matrix and haemorrhage, as well as significant proteoglycan accumulations between SL fibres. These changes are similar to the degeneration of connective tissues in Peruvian Paso horses with SL degeneration and in humans with Cushing's disease or after long term high dose corticosteroid treatments. These findings indicate an association between degeneration of the SL and PPID.