Background
Chronic progressive lameness in young dogs which do not show abnormalities on initial, survey imaging, is diagnostically challenging. The present case had undergone extensive diagnostics without definitive diagnosis until magnetic resonance imaging (MRI) allowed lesion detection and localization to the vertebral venous system. Abnormalities of the vertebral venous system have only previously been reported once in veterinary medicine.

Case presentation
A 1-year-old intact male Standard Poodle was referred with a history of chronic and progressive right thoracic limb lameness. A full work up which included routine haematology, serum biochemistry, radiography, and native computed tomography (CT) of the affected thoracic limb was performed at the referring veterinarian and reported as normal. Management including conventional pain medication, laser treatment, and physiotherapy had been attempted unsuccessfully. Treatment with meloxicam (0.1 mg/kg per os daily) did, however, have some effect on the dog’s pain according to the owner. At our hospital the right thoracic limb lameness was confirmed. A pain reaction was found on manipulation of both shoulders, and a marked muscle atrophy was noted around the right shoulder. On neurological examination, the right thoracic limb had decreased muscle tone and a decreased withdrawal reflex localizing the problem to a right-sided C6-T2 myelopathy or radiculopathy. MRI of the cervicothoracic spine and both brachial plexuses was performed. This showed enlarged internal vertebral venous plexuses especially on the right side from the level of C6 -T2 vertebrae together with marked contrast enhancement of the nerve roots in this region, suggesting nerve root compression secondary to the enlarged venous system. Further analgetic medical management was attempted but due to progression of the dog’s clinical signs, euthanasia was elected 5 months later. Post-mortem investigations confirmed imaging findings and found loss of neurons and swelling of the axons at the compressive sites on histopathology.

Conclusions
Based on the imaging findings a diagnosis of venous plexus abnormalities with secondary radiculopathy was considered most likely. This was confirmed by the post-mortem investigation. Venous plexus abnormalities are rare but should be considered in young dogs with progressive signs of lameness and regional muscle atrophy in which the underlying cause is not identified with conventional diagnostics.