Spinal Cord Hamartomatous Myelodysplasia in 2 Horses With Clinical Neurologic Deficits.
Authors: Taylor K R, MacKay R J, Nelson E A, Stieler A L, Roberts J F, Castleman W L
Journal: Veterinary pathology
Summary
# Editorial Summary Hamartomatous myelodysplasia—a developmental malformation of spinal cord tissue—remains a rare but clinically significant diagnosis in young horses, presenting with varied neurologic manifestations depending on lesion location and severity. Taylor and colleagues documented two cases: a 5-week-old Holsteiner colt with extensor muscle rigidity and spasms, and a 3-year-old Thoroughbred with progressive pelvic limb ataxia and hypermetria, both euthanized following pathological confirmation of focal spinal cord disorganization containing displaced neural tissue, glial cells, and chaotic axon bundles. The Holsteiner's cervical mass at C5 occluded the central canal and caused secondary hydromyelia, whilst the Thoroughbred's lumbar lesion at L1 remained peripheral and non-obstructive, illustrating how anatomical location directly determines clinical severity and progression. These case reports emphasise the importance of advanced imaging and cerebrospinal fluid analysis in young horses presenting with unexplained, progressive neurologic dysfunction, particularly when clinical signs do not align with more common diagnoses such as equine herpesvirus-1 myeloencephalopathy or traumatic spinal cord injury. Early recognition of congenital spinal cord abnormalities allows clinicians to provide appropriate prognostic counselling and avoid prolonged treatment of an ultimately non-responsive condition.
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Practical Takeaways
- •Hamartomatous myelodysplasia should be considered as a differential diagnosis in young horses presenting with unexplained progressive neurologic signs, particularly muscle rigidity or ataxia
- •The location and extent of spinal cord lesions (cervical vs lumbar, central vs peripheral) may influence the specific clinical presentation and severity of neurologic deficits
- •Definitive diagnosis requires advanced imaging (MRI) and histopathological examination; clinical signs alone cannot differentiate this condition from other myelopathies
Key Findings
- •Two horses with hamartomatous myelodysplasia presented with distinct neurologic signs: muscle rigidity in a 5-week-old colt and progressive ataxia with hypermetria in a 3-year-old colt
- •Histopathological examination revealed focal disorganization of spinal cord white and gray matter with interspersed neurons, glial cells, and disoriented axon bundles
- •In the younger horse, the cervical (C5) lesion included meningeal tissue, occluded the central canal, and caused secondary hydromyelia cranial to the obstruction
- •In the older horse, the lumbar (L1) lesion was located on the dorsal spinal cord periphery and did not involve the central canal