A 3-month-old Friesian colt presented with severe, progressive distal limb lameness in two limbs. Radiographic and postmortem full-body CT imaging revealed severe articular deforming osteolysis and osteoproliferation at the dorsodistal navicular bone margin and the adjacent distal phalanx proximo-palmar/proximo-plantar margin in two limbs, with the remainder of the distal interphalangeal joint being unaffected. Multiple other joints showed small osteolytic subchondral defects. Postmortem histopathological examination confirmed focal joint disease of both distal interphalangeal joints, without an identifiable cause. Based on clinical presentation, imaging findings, and histopathology, regional joint maldevelopment was suspected.
