A five year old American Saddlebred gelding was admitted to the Univer
sity of Illinois Veterinary Medical Teaching Hospital with a history o
f multiple leg lameness, depression and intermittent fever for a durat
ion of six months. Physical examination revealed the horse to be under
weight, depressed and afebrile. No abnormalities were detected during
auscultation of the heart and lungs. All limbs possessed multiple hard
swellings of the distal long bones and digits. The horse walked with
a stiff gait and was reluctant to trot. Nuclear scintigraphy of the di
stal limbs revealed multiple areas of focally increased uptake in all
limbs. Radiographs of several sites on the distal limbs showed evidenc
e of periosteal new bone production corresponding to the areas of abno
rmal uptake. The horse was euthanized and at necropsy chronic, multifo
cal, fibrous pericarditis and epicarditis were observed grossly. The l
eft atrial myocardium contained areas of osseous metaplasia. Histologi
cal evaluation of the distal long bones revealed proliferative periost
eal new bone formation consistent with a diagnosis of hypertrophic ost
eopathy.