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David M. Wong Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011.

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Lindsey Gilmour Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011.

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Cody Alcott Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011.

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Michael Yaeger DVM Department of Pathology, College of Veterinary Medicine, Iowa State University, Ames, IA 50011.

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Sarah Wiechert Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011.

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History

A 191-kg (420-lb) 7-month-old Quarter Horse filly was evaluated because of a 1-month history of difficulty rising from recumbency. Tachycardia (60 beats/min) and mild bilateral flexural limb deformities of the metacarpophalangeal and metatarsophalangeal joints were observed on physical examination. The filly would also hold its head and neck to the right while walking and appeared weak and knuckled over on both metacarpophalangeal joints. Further examination revealed neurologic deficits including a dysmetric forelimb gait, weakness (ie, toe dragging) of the left forefoot and both hind feet, and circumduction of the hind limbs (right worse than left) when the filly was moved in tight circles. Additionally, the filly had reduced range of motion of the cervical vertebral column, especially when manipulating the head and neck to the left. Neurolocalization suggested a cervical myelopathy. Results of a CBC and biochemical analysis were unremarkable, as were survey cervical radiographs. Computed tomographic myelography was subsequently performed of the osseous and soft tissue structures within the cervical vertebral column (Figure 1).

Figure 1—
Figure 1—

Transverse CT images of the cervical vertebral column in a 7-month-old Quarter Horse filly evaluated because of neurologic deficits including paresis, forelimb dysmetria, and difficulty rising from recumbency. The patient's right side is to the left of each image. A—Soft tissue window (slice thickness, 2 mm; window width, 400 Hounsfield units [HU]; window level, 40 HU) CT myelogram obtained at the plane of the C6–7 articular process joint space. B—Bone tissue window (slice thickness, 2 mm; window width, 2,000 HU; window level, 400 HU) CT myelogram obtained at the plane of C7, approximately 1.2 cm caudal to the image in panel A.

Citation: Journal of the American Veterinary Medical Association 248, 1; 10.2460/javma.248.1.55

Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →

Diagnostic Imaging Findings and Interpretation

The filly was anesthetized and imaged in dorsal recumbency following intrathecal administration of 60 mL of iohexol. Contiguous axial images were obtained with a 16-slice helical scannera in soft tissue and bone algorithms from the level of the occipital condyles through T1. Multiplanar reconstructed images were made on a dedicated workstation.

On CT evaluation, mild attenuation of the myelographic contrast column ventrally along the spinal cord at the level of the caudal aspect of C6 and along the left dorsal aspect of the spinal cord at the level of C7 is evident (Figure 2). The subchondral bone of the left cranial articular process of C7 has a small, concave defect. A thin, curvilinear, mineral density within the soft tissues immediately adjacent to the caudal extent of the left articular process joint of C6–7 is evident. The left dorsal lamina of C7 is bulbous in a plane caudal to the left C6–7 articular process joint space. These changes are consistent with chronic, mild degenerative joint disease of the left articular process at C6–7. The curvilinear mineral feature dorsal to the left C6–7 process joint may be dystrophic mineralization within the joint capsule or a mineralized joint body. Possible underlying pathological processes included osteochondrosis, osteochondritis dissecans (OCD), or trauma. On the basis of the young age of the patient without a history of trauma, the leading differential diagnoses were osteochondrosis or OCD.

Figure 2—
Figure 2—

Same images as in Figure 1. A—The myelographic contrast column is narrowed dorsolaterally along the left side. A small, concave defect is present in the subchondral bone of the left cranial articular process of C7 (solid black arrow). A hyperattenuating curvilinear area is present within the soft tissues dorsolateral to this joint (open black arrow). B—The dorsal laminae of C7 are asymmetric, and there is a bulbous thickening of the bone on the left side (white arrow).

Citation: Journal of the American Veterinary Medical Association 248, 1; 10.2460/javma.248.1.55

Flexed and extended right lateral radiographsb of the cervical vertebral column were subsequently acquired while the filly was still anesthetized (Figure 3); these images revealed mild narrowing of the dorsal and ventral contrast columns at C6–7 when the neck was in extension. Radiographic and CT images were consistent with mild compressive myelopathy at the level of C6–7.

Figure 3—
Figure 3—

Lateral radiographic image of the caudal cervical vertebral column of the same filly as in Figure 1. The image was obtained with the head and neck in extension with the horse under general anesthesia. Approximately 50% and 100% narrowing of the dorsal and ventral contrast columns, respectively (arrows), at C6–7 is evident.

Citation: Journal of the American Veterinary Medical Association 248, 1; 10.2460/javma.248.1.55

Treatment and Outcome

Cerebrospinal fluid was collected from the atlantooccipital joint space prior to administration of iohexol; no abnormalities were detected on cytologic evaluation of CSF, and the total protein concentration was within reference range. On the basis of diagnostic imaging, clinical signs, and unremarkable clinicopathologic findings, an OCD lesion involving the C6–7 vertebrae was highly suspected and a tentative diagnosis made. Because of the limited medical treatment options and poor prognosis for return to function, the filly was euthanized.

Gross necropsy confirmed an OCD lesion of the left articular process of C6–7 characterized as a 1.5 × 1-cm cartilaginous flap covering an irregular focus of erosion and ulceration of the articular cartilage. Mild axonal degeneration was observed on histologic examination of the adjacent segments of spinal cord, indicating that the OCD lesion and associated spinal cord degeneration contributed to the neurologic signs. Mild, widely scattered perivascular inflammatory foci were also observed in the adjacent spinal cord and were speculated to be associated with the inflammatory response occurring during remodeling from the instability of the cervical vertebrae.

Comments

The early definition of osteochondrosis implied an underlying lesion in the joint cartilage that facilitated formation of loose bodies in the absence of major trauma.1 Subsequently, this term has evolved to describe a developmental orthopedic disease caused by the formation of cartilaginous clefts extending through articular cartilage into the subchondral bone.1 Clinically, when a fissure or fracture in the overlying articular cartilage is present, the condition is commonly referred to as OCD and describes a situation in which epiphyseal growth cartilage becomes separated from the underlying subchondral bone and is accompanied by a reactive inflammatory response at the bone surface beneath the line of separation.1,2 Simply stated, osteochondrosis is the disease, osteochondritis is the inflammatory response to the disease, and OCD is the condition in which a flap of cartilage or osteochondral separation is present.2 Although OCD is one of the most serious skeletal disorders in growing horses and commonly affects the appendicular skeleton, OCD lesions of the cervical vertebrae have been infrequently reported.3–5

Specific osteochondritic cervical lesions described in individual case reports include symmetric osteochondrosis of the occipital condyles in a 14-month-old Belgian gelding with severe ataxia of all limbs3; a cartilage flap defect of the cranial articular process of C2 in a 2-year-old male Thoroughbred with no neurologic deficits except signs of neck pain, abnormal neck position (head constantly tilted to the right and neck extended), and reluctance to graze from the ground4; and osteochondrosis of multiple cervical vertebrae (C3 through C7) in a 16-month-old American Paint Horse filly that was reluctant to walk.5

The filly of the present report had similar clinical signs as those previously reported, such as abnormal head and neck carriage, reduced range of neck motion, a weak and dysmetric gait, and proprioceptive deficits.3–5 These clinical signs were attributed to an OCD lesion of the left articular process of C6–7 on the basis of clinical examination, CT imaging, and results of gross and histologic evaluation of the spinal cord in this region.

The appearance of osteochondrotic lesions on diagnostic images will vary between horses and anatomic areas involved, but radiographic changes may include discrete osteochondral fragments, alterations in the contour of the articular surface, irregularly shaped lucent zones in the subchondral bone, sclerosis surrounding the lucent zones, or secondary remodelling of joints.6 Interestingly, although narrowing of the dorsal and ventral contrast columns at C6–7 was observed with contrast radiography in the filly of the present report, no other abnormal findings were identified through survey or myelographic radiography. Conversely, CT imaging correctly identified and detailed the anatomic lesion in the filly of the present report. However, in adult horses, CT imaging of the cervical region may be limited by the size of the horse, allowing CT imaging only up to C6 in larger horses. To the authors’ knowledge, this is the first reported case in which CT imaging was used to identify a specific OCD lesion of the cervical vertebra and associated tissue remodeling as the underlying cause of the neurologic deficits observed in a horse, and the case illustrates the benefit of advanced imaging to facilitate a diagnosis.

Footnotes

a.

Aquilion 16, Toshiba, Tokyo, Japan.

b.

Optimus, Koninklijke Philips NV, Amsterdam, The Netherlands.

References

  • 1. McCoy AM, Toth F, Dolvik NI, et al. Articular osteochondrosis: a comparison of naturally-occurring human and animal disease. Osteoarthritis Cartilage 2013; 21: 16381647.

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  • 2. McIlwraith CW. Surgical versus conservative management of osteochondrosis. Vet J 2013; 197: 1928.

  • 3. Muirhead T, McClure JT, Bourque A, et al. Osteochondrosis of the occipital condyles and atlanto-occipital dysplasia in a Belgian horse. Can Vet J 2003; 44: 984986.

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  • 4. Beck C, Middleton D, Mcclean A, et al. Osteochondrosis of the second cervical vertebra of a horse. Equine Vet J 2002; 34: 210212.

  • 5. Girard C, Lepage OM, Rossier Y. Multiple vertebral osteochondrosis in a foal. J Vet Diagn Invest 1997; 9: 436438.

  • 6. Butler JA, Colles CM, Dyson SJ, et al. General principles. In: Butler JA, Colles CM, Dyson SJ, et al, eds. Clinical radiology of the horse. Oxford, England: Blackwell Scientific Publications, 1993; 124.

    • Search Google Scholar
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  • Figure 1—

    Transverse CT images of the cervical vertebral column in a 7-month-old Quarter Horse filly evaluated because of neurologic deficits including paresis, forelimb dysmetria, and difficulty rising from recumbency. The patient's right side is to the left of each image. A—Soft tissue window (slice thickness, 2 mm; window width, 400 Hounsfield units [HU]; window level, 40 HU) CT myelogram obtained at the plane of the C6–7 articular process joint space. B—Bone tissue window (slice thickness, 2 mm; window width, 2,000 HU; window level, 400 HU) CT myelogram obtained at the plane of C7, approximately 1.2 cm caudal to the image in panel A.

  • Figure 2—

    Same images as in Figure 1. A—The myelographic contrast column is narrowed dorsolaterally along the left side. A small, concave defect is present in the subchondral bone of the left cranial articular process of C7 (solid black arrow). A hyperattenuating curvilinear area is present within the soft tissues dorsolateral to this joint (open black arrow). B—The dorsal laminae of C7 are asymmetric, and there is a bulbous thickening of the bone on the left side (white arrow).

  • Figure 3—

    Lateral radiographic image of the caudal cervical vertebral column of the same filly as in Figure 1. The image was obtained with the head and neck in extension with the horse under general anesthesia. Approximately 50% and 100% narrowing of the dorsal and ventral contrast columns, respectively (arrows), at C6–7 is evident.

  • 1. McCoy AM, Toth F, Dolvik NI, et al. Articular osteochondrosis: a comparison of naturally-occurring human and animal disease. Osteoarthritis Cartilage 2013; 21: 16381647.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 2. McIlwraith CW. Surgical versus conservative management of osteochondrosis. Vet J 2013; 197: 1928.

  • 3. Muirhead T, McClure JT, Bourque A, et al. Osteochondrosis of the occipital condyles and atlanto-occipital dysplasia in a Belgian horse. Can Vet J 2003; 44: 984986.

    • Search Google Scholar
    • Export Citation
  • 4. Beck C, Middleton D, Mcclean A, et al. Osteochondrosis of the second cervical vertebra of a horse. Equine Vet J 2002; 34: 210212.

  • 5. Girard C, Lepage OM, Rossier Y. Multiple vertebral osteochondrosis in a foal. J Vet Diagn Invest 1997; 9: 436438.

  • 6. Butler JA, Colles CM, Dyson SJ, et al. General principles. In: Butler JA, Colles CM, Dyson SJ, et al, eds. Clinical radiology of the horse. Oxford, England: Blackwell Scientific Publications, 1993; 124.

    • Search Google Scholar
    • Export Citation

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