The main pathology is located in the epiphyses.

The proximal and distal epiphysis of both humeri, as well as the proximal epiphysis of both radii and femora are markedly deformed. The epiphyses are reduced in height and even partially absent (shoulder joints); they appear stippled with a heterogeneous opacity. The joint surfaces are markedly irregular incongruent. The underlying bone is sclerotic. Shoulder, elbow and stifle joints show a moderate to severe increase in soft tissue opacity.

Smooth, slightly heterogenous periostal new bone formation is present on the proximal humeral metaphyses resulting in a nose-like caudal protrusion. The underlying bone is sclerotic.

The glenoid cavity of both humeri is shallow. Smooth and solid new bone formation is present on the cranio-lateral aspect of the cranial and caudal acetabular edges.

The right femoral head is collapsed with a flattened cranial aspect. The left femoral head is flattened medially.

The distal epiphyses of both radii, ulnae, both tibial and fibular epiphyses as well as both tibial tuberosities are decreased in height but still result in a smooth articular surface.
The carpal and tarsal bones are of normal size but the bones show a coarse trabecular pattern.
The sacrum consists of only 2 vertebrae. The 3rd sacral vertebra is separate from the second. Otherwise the lumbar spine is unremarkable.

• Epiphyseal dysplasia in the appendicular skeleton with pathological fractures of some of the epiphyses. Associated secondary osteoarthritis

Differential diagnoses for epiphyseal dysplasia include mucopolysaccharidosis, mucolipidosis, congenital chondrodysplasia, hypothyroidism and pituitary dwarfism.

In the current case mucopolysaccharidosis is considered the most likely differential diagnosis. Mucolipidosis is possible but very rare and usually lead to less severe epiphyseal changes. A congenital chondrodysplasia is less likely, as this usually leads to delayed of ossification of the small cuboid bone of the carpal and tarsal joint as well, which appear markedly reduced in size. In the case presented here the carpal and tarsal joints are not entirely normal, however the size of the cuboid bones is physiological.

Hypothyroidism is unlikely as changes usually also affect the epiphysis of the spine.
Pituitary dwarfism is unlikely due to the normal appearance of the physes. Pituitary dwarfism leads to delayed physeal closure, epiphyseal changes are also possible but do not represent the main finding.