A fast-growing Thoroughbred horse with progressive ataxia starting from the rear limbs most likely has which condition?

• A. Equine degenerative myeloencephalopathy
• B. Wobbler's disease (cervical vertebral instability)
• C. Cerebellar hypoplasia
• D. Poliomyelitis

Answer: (B)

The situation points to a lesion compressing the spinal cord in a young, fast-growing horse, with ataxia that begins in the hind limbs and can progress as growth-related instability of the cervical spine worsens. This pattern fits Wobbler’s disease (cervical vertebral instability) best. In rapidly growing Thoroughbreds, malformation or instability of the cervical vertebrae can cause dynamic compression of the cervical spinal cord, so proprioceptive pathways that run to the hind limbs are affected first. The horse becomes uncoordinated and wobbly, often with a characteristic hindlimb-centric progression, which matches the presentation described.

Other possibilities don’t align as well with this scenario. Cerebellar hypoplasia produces intention tremors and a wide-based stance from birth, not a progressive hindlimb-dominant ataxia that starts as the horse grows. Equine degenerative myeloencephalopathy is a degenerative, often symmetric proprioceptive disorder usually linked to vitamin E deficiency in young horses, not a progressive, limb-by-limb spinal cord compression starting in the rear limbs. Poliomyelitis affects the ventral horn motor neurons, causing LMN-type weakness or paralysis rather than the spinal-cord–based ataxia described.