What Is Your Neurologic Diagnosis?

Aran Nagendran Neurology/Neurosurgery Service, Hospital for Small Animals, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Edinburgh EH25 9RG, Scotland.

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Nina Rzechorzek Neurology/Neurosurgery Service, Hospital for Small Animals, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Edinburgh EH25 9RG, Scotland.

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Tiziana Liuti Neurology/Neurosurgery Service, Hospital for Small Animals, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Edinburgh EH25 9RG, Scotland.

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Katia Marioni-Henry Neurology/Neurosurgery Service, Hospital for Small Animals, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Edinburgh EH25 9RG, Scotland.

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A A 6-month-old 4.3-kg (9.5-lb) sexually intact male Pug was evaluated because of a 10-day history of abrasions on the dorsum of the forepaws and a 3-month history of hypermetric gait. Results of a general physical examination were unremarkable except for facial fold dermatitis and focal areas of alopecia on the dorsal aspects of both forefeet.

What is the problem? Where is the lesion? What are the most probable causes of this problem? What is your plan to establish a diagnosis? Please turn the page.

Assessment Anatomic diagnosis

ProblemRule out location
Postural reaction deficits in all 4 limbs causing abrasions on the dorsum of both forefeet (slightly more severe on the right side)Focal central C1-C5 spinal cord lesion (slightly lateralized to the right)
Thoracic limb hypermetria; general proprioceptive ataxia and mild tetraparesis (more evident in the pelvic limbs)C1-C5 spinal cord segments

Likely location of 1 lesion

Right-lateralized spinal cord lesion within the C1-C5 region

Etiologic diagnosis—Given the dog's signalment, differential diagnoses considered for a mildly progressive nonpainful lesion in the C1-C5 region of the spinal cord included congenital anomalies (vertebral malformation [eg, hemivertebrae]) and space-occupying lesions (eg, arachnoid diverticulum, syringomyelia, and intramedullary neoplasia). Inflammatory or infectious causes of myelitis (eg, infection with Toxoplasma sp or Neospora sp) were also considered. The diagnostic plan included hematologic, biochemical, and specific antibody analyses and PCR testing of a blood sample (to assess for infectious disease and evaluate liver function [in light of previous abnormal biochemical findings]); radiography and MRI of the vertebral column (to rule out vertebral malformations); and analysis of a CSF sample collected from the cisterna magna (to evaluate for inflammatory, infectious, or neoplastic disease).

Diagnostic test findings—Results of hematologic analyses were unremarkable. Repeated in-house serum biochemical analyses revealed persistently high activities of alkaline phosphatase (718 U/L; reference range, 20 to 150 U/L) and alanine aminotransferase (917 U/L; reference range, 10 to 118 U/L); however, the result of a bile acids stimulation test was normal. Screenings for anti-Toxoplasma and anti-Neospora antibodies were negative, and radiographic findings were unremarkable. The dog underwent an MRIa examination of the vertebral column, and multiplanar T1-weighted images, T2-weighted images, and T1-weighted images obtained following IV administration of gadolinium were acquired. Magnetic resonance imaging revealed a focal widening of the dorsal arachnoid space from the cervicomedullary junction to the level of the cranial aspect of C3 (Figure 1), consistent with a cervical arachnoid diverticulum. Caudal to the arachnoid lesion on T2-weighted images, there was a linear, wedge-shaped hyperintensity in the dorsal aspect of the spinal cord, which extended from C3 through to C5, suggestive of syringomyelia. Findings of routine CSF analysis were normal, and the result of a PCR assay for canine distemper virus was negative.

Figure 1—
Figure 1—

Magnetic resonance images of the vertebral column of a 6-month-old Pug that was evaluated because of a 10-day history of abrasions on the dorsum of the forepaws and a 3-month history of hypermetric gait. A—Sagittal T2-weighted image of an intradural arachnoid diverticulum (indicated by line B) with syringomyelia (indicated by line C). B—Transverse T2-weighted image (obtained at the level of line B in panel A) of a hyperintense dilation of the dorsal subarachnoid space (arrow), which is compressing the spinal cord. C—Transverse T2-weighted image (obtained at the level of line C in panel A) of a hyperintense dilation of the dorsal subarachnoid space (arrow). R = Right. L = Left.

Citation: Journal of the American Veterinary Medical Association 250, 11; 10.2460/javma.250.11.1235

Comments

Cervical spinal intradural arachnoid diverticula (SIAD) are an uncommon cause for compression of the cervical portion of the spinal cord. In dogs, these lesions have been described as arachnoid-leptomeningeal cysts, leptomeningeal cavitations, or even pseudocysts. Because these lesions lack an epithelial lining, the term cyst is misleading. Spinal intradural arachnoid diverticula can develop at any level of the spinal cord but are most often present in the cranial cervical and caudal thoracic regions.1,2 In a study3 of 14 dogs with SIAD, large-breed dogs, namely Rottweilers, were overrepresented (8/14 dogs) with diverticula typically located in the cranial cervical area; in the 6 small-breed dogs, lesions were identified most often in the thoracolumbar region.3 Another study1 of 122 affected dogs revealed that Pugs were overrepresented with most of the SIAD located in the thoracolumbar region. There have been few reports3,4 of cervical SIAD in young Pugs. The etiopathogenesis of SIAD is incompletely understood and is considered to be multifactorial. Findings of a recent study4 suggested a genetic predisposition in Pugs. Spinal intradural arachnoid diverticula result in an accumulation of CSF within the space between the arachnoid tissue and the pia mater. Clinical signs associated with this condition include progressive proprioceptive ataxia or paresis, but rarely signs of pain.2 Compression of the dorsal aspect of the spinal cord at this location would affect the sensory components of proprioception with the fasciculi cuneatus and gracilis comprising the lemniscal pathways. This gives rise to a characteristic stomping gait as the impact of the foot hitting the ground rather than touch or proprioception guides the walk. A long-strided gait with limited flexion of the carpi and tarsi is also seen, suggestive of an upper motor neuron paresis with proprioceptive ataxia. By contrast, the hyperflexive gait of cerebellar ataxia is characterized by overreaching with preserved flexion of the carpi.5

Resection of SIAD is currently the preferred treatment in both veterinary and human medicine.4,6 The dog of the present report underwent a dorsal laminectomy at the C3 vertebra. A 3 × 3-mm discoloration of the dura was identified. After durectomy, the spinal cord regained a normal appearance. The dorsal lamina of C3 was reconstructed with titanium mesh.

Previous reports have indicated a variable outcome following resection of SIAD in dogs. In 1 study,3 surgical intervention to treat SIAD appeared to be associated with a more favorable outcome in dogs with a cervical lesion, compared with the outcome in dogs with a thoracolumbar lesion; of the 11 dogs available for follow-up, 7 had neurologic improvement. However, most dogs with a cervical lesion in that study3 were large breeds. Reports1,4 of SIAD indicate that they are usually acquired and not associated with syringomyelia. Rohdin et al4 first reported cervical SIAD with associated syringomyelia in related Pugs and proposed an inherited congenital etiology. They also reported variable treatment outcomes, with 2 of 3 Pugs that underwent surgical treatment subsequently being euthanized. Two of the 4 Pugs that were conservatively managed were still alive at the time of that report.4 It is not clear whether surgical or conservative treatment of the SIAD could have been affected by the concurrent syringomyelia because MRI examinations were not repeated for any of the Pugs.

For young Pugs with progressive nonpainful hypermetria and proprioceptive deficits in all 4 limbs, differential diagnoses should include cervical SIAD. In cases of acquired SIAD, surgical treatment can lead to improved neurologic function in the short term, although the reported recurrence rate is high (30%).2 For the dog of the present report, surgical treatment resulted in improvement in the degree of hypermetria, but general proprioceptive ataxia and mild tetraparesis remained. Further studies are required to better understand the causes and progression of cervical SIAD with associated syringomyelia in young Pugs to provide appropriate treatment and breeding recommendations.

Footnotes

a.

Philips Intera 1.5T Pulsar System, Philips Medical Systems, Guildford, Surrey, England.

References

  • 1. Mauler DA, De Decker S, De Risio L, et al. Signalment, clinical presentation, and diagnostic findings in 122 dogs with spinal arachnoid diverticula. J Vet Intern Med 2014; 28: 175181.

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  • 2. Skeen TM, Olby NJ, Muñana KR, et al. Spinal arachnoid cysts in 17 dogs. J Am Anim Hosp Assoc 2003: 39: 271282.

  • 3. Rylander H, Lipsitz D, Berry WL, et al. Retrospective analysis of spinal arachnoid cysts in 14 dogs. J Vet Intern Med 2002; 16: 690696.

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  • 4. Rohdin C, Nyman HT, Wohlsein P, et al. Cervical spinal intradural arachnoid cysts in related, young Pugs. J Small Anim Pract 2014; 55: 22934.

  • 5. Platt S, Garosi L. Ataxia. In: Platt S, Garosi L, eds. Small animal neurological emergencies. London: Manson Publishing, 2012; 193204.

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  • 6. Hughes G, Ugokwe K, Benzel EC, et al. A review of spinal arachnoid cysts. Cleve Clin J Med 2008; 75: 311315.

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