Myelodysplasias
Mary O. Smith • Robert J. MacKay
The following types of myelodysplasia occur in livestock1-15:
1. Spinal dysraphism. Abnormal development of the spinal cord before complete differentiation of gray and white matter; the areas of agenesis form longitudinal cystic structures instead of differentiated nervous tissue.
Most of these anomalies are neural tube defects.2. Syringomyelia. Longitudinal fluid-filled cavitations of the spinal cord.
3. Hydromyelia. Abnormal fluid-filled dilation of the central canal.
4. Diastematomyelia. Duplication of the gray matter at one or more segments.
5. Racbischisis. Complete failure of the neural tube to close; the central canal remains exposed and communicates with the integument.
6. Meningocele. Herniation of the meninges through a vertebral defect (usually spina bifida).
7. Meningomyelocele. Herniation of the meninges and dysplastic spinal cord through a spinal column defect.
8. Myelodysplasia without vertebral defects.
Associated abnormal neurologic signs are as described earlier for spina bifida.
Myelodysplasia has been related to genetic factors in Charolais and Hereford calves, although the mode of inheritance is unknown.3,16 The condition has also been recognized in foals of several breeds.15,17-19 In addition to genetic factors, causes include intrauterine bunyavirus (Schmallenberg, Akabane, Cache Valley, and Aino virus) infections, hypovitaminosis A or copper deficiency, maternal fever, or exposure to teratogens, including substances in species of Solanum and Veratrum.15,20
The neurologic deficits of myelodysplasia are difficult to differentiate from other spinal diseases unless the disorder is accompanied by spina bifida. Clinical recognition of myelodysplasia is usually based on the historical findings of paraplegia in a newborn calf without radiographic evidence of spinal fractures and with no myelographic evidence of spinal cord compression.