A 6-months-old male crossbreed Golden Retriever was referred for occasional signs of hind lameness with abnormal gait. When he was 4 months old, the owners noticed some painless swellings on the left foreleg but they thought they were related to possible injuries. Since then, the swellings have increased in size and nowadays the dog can only stand still for a few seconds before crying in pain.
At physical examination, two compacted and well defined bone enlargements situated at proximal humerus and proximal radius. We proceed to anesthetize the dog and radiograph the whole body. The X-rays showed numerous exostoses at the spinous processes of the thoracic vertebrae, three exostoses at the rib cage and bone formations at the proximal humerus and radius. The exostoses of the vertebrae and rib cage have a round form and the ones on the extremities are more elongated with higher radiodensity, well delimited and an apparent continuity with the bone cortex.
On the base of the radiological lesions an initial diagnosis of multiple cartilaginous exostoses (MCE) with poor or reserved prognosis was established. Due to a successive pain crisis, every time more intense and uncontrollable with AINS, the animal was euthanized by owner's petition. At histopathological study all the exostosis showed a similar pattern with a central area of woven bone and cartilage with different degrees of ossification delimited externally with an hyaline cartilage cap. The histological study confirmed the clinical diagnosis of osteochondromatosis.
The terminology of this pathology varies a lot. Exists up to 14 different synonyms. Generally the most accepted term is multiple cartilaginous exostoses (MCE) when several lesions exist in the same animal and osteochondroma when only one is found. The MCE has been described in humans, dogs, horses and cats. It characterizes for the presence of anomalous bone proliferation on the metaphysis of the bone with endochondral ossification. The most affected bones, apart from the long ones, are the vertebrae and ribs. The bones with intramembranous ossification origin are not affected.
The exact etiology is unknown, although in humans it could have an inherited character linked to an autosomal dominant gene. One of the possible theories for the etiology talks about the ectopic ubication during the development of the growth cartilage cores that in their new placement will follow the endochondral ossification process, building up the different exostoses.
Other theories are based on the possible change of polarity of some cartilaginous cells that will adopt an anomalous position of the bone, or on the alteration of the osteogenic layer of the periosteum. The clinical signs are generally related with the physical effect of the exostoses on the adjacent structures. Neurological symptoms related to spinal compressions are common. In these cases, it is advised surgery to remove the exostoses. Although it is a benign process, it has been described as cases of neoplastic transformation in dogs more than 7 years old.