What Is Your Neurologic Diagnosis?

Emili Alcoverro Small Animal Teaching Hospital, School of Veterinary Science, Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Neston, Wirral, England

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Camilla Jayne Cooper Small Animal Teaching Hospital, School of Veterinary Science, Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Neston, Wirral, England

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Martina Piviani Small Animal Teaching Hospital, School of Veterinary Science, Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Neston, Wirral, England

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Lorenzo Ressel Department of Veterinary Anatomy, Physiology and Pathology, School of Veterinary Science, Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Neston, Wirral, England

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Fraser James McConnell Small Animal Teaching Hospital, School of Veterinary Science, Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Neston, Wirral, England

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Daniel Sánchez-Masián Small Animal Teaching Hospital, School of Veterinary Science, Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Neston, Wirral, England

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Introduction

A 7-year-old 2.7-kg neutered female Yorkshire Terrier was referred for evaluation of a 3-month history of progressive cervical pain, intermittent right-sided head tilt, and episodic right-sided cervical pruritus. Topical treatment with fusidic acid and betamethasone for suspected bilateral ear disease and oral administration of gabapentin were started by the primary veterinarian. Short courses of tramadol, omeprazole, and potentiated amoxicillin were also instigated. No improvement of the clinical signs was documented. Results of a physical examination were normal.

Assessment

Anatomic diagnosis

The dog had a mild, intermittent, right-sided head tilt with alert mentation, normal cranial nerve function, a normal gait, and intact postural reactions, which, taken together, was suggestive of a lesion involving the right peripheral vestibular system or the spinal nerves, dorsal spinal nerve roots, or dorsal gray matter of the first 3 cervical spinal cord segments (ie, the spinovestibular tracts). The right cervical muscle atrophy was most likely a result of a lesion involving the right cervical spinal cord segments, right cervical spinal nerves, or right external branch of the accessory nerve. The cervical hyperesthesia was suggestive of a lesion involving the meninges, spinal nerve roots, or spinal nerves.

Likely location of a single lesion

Right cranial cervical spinal nerves or right cranial cervical spinal cord.

Etiologic diagnosis

The primary differential diagnoses for a chronic, progressive cervical myelopathy or cranial cervical neuropathy in a 7-year-old dog included neoplastic process (eg, peripheral nerve sheath tumor), inflammatory neuropathy (eg, chronic hypertrophic ganglioneuritis), inflammatory myelopathy or neuropathy (eg, meningomyelitis or neuritis of unknown etiology), and lateralized or foraminal intervertebral disk herniation. A right-sided peripheral vestibular neuropathy or otitis interna could also have explained the intermittent right-sided head tilt. Differential diagnoses for this included otitis media–otitis interna and neoplasia.

Diagnostic Plan

The diagnostic plan consisted of a CBC and serum biochemical analyses, MRI of the cervical vertebral column and head, and CSF analysis.

Diagnostic Test Findings

The CBC and serum biochemical analyses did not reveal any clinically important abnormalities. Magnetic resonance imaging was performed with a commercial unit with a 1.5-T permanent magnet (Ingenia 1.5T CX; Philips Medical System). The dog was positioned in dorsal recumbency, and transverse, dorsal, and sagittal T2-weighted images; transverse T1-weighted images; transverse FLAIR images; and transverse T2*-weighted images of the head were obtained, along with balanced fast field echo images of the cranial portion of the cervical spine. Transverse, dorsal, and sagittal T1-weighted images were also obtained after IV administration of gadopentetate dimeglumine (gadobutrol; Gadovist).

Magnetic resonance imaging revealed focal enlargement of the dorsal and ventral roots of the right C2 nerve and a multilobular mass arising from the C2 nerve (Figures 1 and 2). The mass extended laterally through the C1-2 intervertebral foramen for approximately 2.5 cm and involved both the dorsal and ventral branches of the nerve and its ganglion. The mass had heterogeneous signal intensity on T2-weighted images, with low signal intensity of the nerve roots, intermediate to high signal intensity of the nerve mass, and lower signal intensity of the mass periphery. On T1-weighted images, the mass had intermediate signal intensity, and on postcontrast images, there was homogenous, dense contrast enhancement of the mass. Mild abnormal meningeal contrast enhancement was present adjacent to the abnormal C2 nerve roots. The mass caused mild compression of the spinal cord at C1-C2. No extension of the mass into the spinal cord was visible, but T2-weighted images showed a focal, ill-defined intramedullary hyperintensity adjacent to the abnormal C2 nerve. The muscles dorsal and ventromedial to the right transverse process of C2 were reduced in size, with homogenous increased signal intensity on T2-weighted images, intermediate signal intensity on T1-weighted images, and mild homogenous contrast enhancement, consistent with denervation. Additional abnormalities included Chiari-like malformation with atlanto-occipital overlapping and a dorsal atlantoaxial band causing mild dorsal compression of the spinal cord at C1-C2.

Figure 1
Figure 1

Transverse T2-weighted MRI image at the level of C1-C2 in a 7-year-old Yorkshire Terrier with a 3-month history of progressive cervical pain, intermittent right-sided head tilt, and episodic right-sided cervical pruritus. The nerve roots and proximal portion of the right C2 nerve (arrows) are enlarged with heterogeneous signal intensity. The enlarged nerve roots compress the adjacent spinal cord, which has increased signal intensity.

Citation: Journal of the American Veterinary Medical Association 260, 10; 10.2460/javma.21.01.0005

Figure 2
Figure 2

Dorsal T1-weighted postcontrast MRI image of the cranial cervical spine. The enlarged C2 nerve and nerve roots (arrows) show abnormal, dense contrast enhancement.

Citation: Journal of the American Veterinary Medical Association 260, 10; 10.2460/javma.21.01.0005

A lumbar CSF sample was collected. The cell count was 4 nucleated cells/μL (reference interval, < 5 cells/μL), and microscopic examination of a cytospin slide did not reveal any clinically important cytologic abnormalities. The sample contained predominantly small lymphocytes with fewer large monocytoid cells. The protein concentration could not be measured owing to insufficient sample volume.

Ultrasound-guided fine-needle aspirates of the enlarged nerve root were obtained. Slide preparations of the aspirate were poorly cellular with scant RBCs and a few spindle cells with an oval nucleus, finely granular chromatin, 1 or 2 light-blue nucleoli, and scant light-blue cytoplasm. Anisocytosis and anisokaryosis were mild. Findings were compatible with reactive fibroplasia or mesenchymal neoplasia, but the low cell yield and mild degree of atypia precluded a more definitive interpretation. The nerve root lesion was considered to most likely be a neoplastic disease (eg, peripheral nerve sheath tumor) or an inflammatory process (eg, chronic hypertrophic ganglioneuritis) that had not responded to glucocorticoid or antimicrobial treatment.

Treatment

Pain management was instituted with gabapentin (9.3 mg/kg, PO, q 8 h) and paracetamol (9.3 mg/kg, PO, q 8 h), and immunosuppressive treatment with prednisolone (1.9 mg/kg, PO, q 24 h) was instigated. Three weeks later, in light of a lack of improvement, cyclosporine (5 mg/kg, PO, q 24 h) and amantadine (3.7 mg/kg, PO, q 24 h) were added to the treatment regimen but with no amelioration of the clinical signs. Five weeks after initial presentation, a right-sided hemilaminectomy was performed at the level of the C1-2 intervertebral space. After a durotomy was performed, a firm grayish mass located along the right dorsal aspect of the spinal cord was exposed. The mass was originating from the right C2 nerve and seemed to involve both the dorsal and ventral roots. The mass appeared to infiltrate the spinal cord parenchyma. A fascicular biopsy of the spinal nerve was obtained by means of right-sided C2 rhizotomy. No intraoperative complications were recorded.

Histologic examination of the biopsy specimen identified a well-delimited, nonencapsulated neoplastic proliferation composed of loosely arranged, well-differentiated spindle cells forming whorls surrounding small areas of collagen. Mitoses were not seen, and anisokaryosis and anisocytosis were mild; no associated inflammation was noted.

The histologic features were those of a well-differentiated spindle cell tumor suggestive of a peripheral nerve sheath tumor; however, the particular architecture was more properly consistent with a neurofibroma, as previously described for classification of tumors in humans.1 The possibility of chronic hypertrophic ganglioneuritis as described by Ródenas et al2 was considered unlikely owing to the lack of inflammation associated with the lesion and the evidence of a typical neurofibroma pattern.

Postoperative care consisted of multimodal analgesia (opioids, gabapentin, paracetamol, and continuous rate infusions of ketamine and lidocaine) and prednisolone at an anti-inflammatory dosage. At the time of discharge 5 days after surgery, the dog was ambulatory with moderate right-sided hemiparesis. Postural response deficits of the right thoracic and pelvic limbs were observed, but no neck discomfort or head tilt were noted. Progressive right-sided hemiparesis was reported, and the owner elected euthanasia 35 days after surgery. No postmortem examination was performed.

Comments

Clinical signs and MRI findings for the dog described in the present report were compatible with either peripheral nerve sheath tumor or chronic hypertrophic ganglioneuritis.24 Cytologic findings were compatible with spindle cell proliferation with limited atypia, and histologic examination confirmed the diagnosis of peripheral nerve sheath tumor.

In dogs, peripheral nerve sheath tumors arise from Schwann cells, perineural fibroblasts, or both.5 These tumors were classified in human medicine as peripheral nerve sheath tumors by the World Health Organization in 2013.6 The Schwann cell is the primary neoplastic cell of neurofibromas. In contrast to the microscopic features of schwannomas, neurofibromas are composed of very slender, elongated cells with characteristic buckled or wavy nuclei in a fibromyxoid stroma with thin, wire-like collagen fibers. Schwannomas and neurofibromas are further subclassified according to their growth patterns (schwannomas are classified as localized or plexiform, and neurofibromas are classified as localized, plexiform, or diffuse) and histopathologic features (eg, classic, collagenous, cellular, and pigmented).1 Our case had architectural features consistent with a classic type neurofibroma with some areas resembling a collagenous type. In canine patients, neurofibromas arising from the skin (ie, dermis and subcutis),1 tongue,1 large intestine,1 distal ulnar nerve,1,7 and vagina8 and a suspected neurofibroma arising from the retrobulbar region9 have been reported. Although neurofibromas involving the ulnar nerve in dogs have been described,1,7 to the authors’ knowledge, the present report represents the first description of a neurofibroma arising from a spinal nerve root.

An inflammatory nerve root or dorsal ganglion disease was considered a possibility for the dog of the present report on the basis of clinical signs and MRI findings. In a retrospective study4 of 12 dogs with suspected idiopathic C2 hypertrophic ganglioneuritis, all cases had bilateral C2 nerve root swelling and contrast enhancement with various degrees of spinal cord compression or distortion. Eleven of these dogs were large-breed dogs, and 4 had neck pain. All dogs with clinically important lesions improved following treatment with corticosteroids. Interestingly, a case report2 of histologically confirmed, unilateral, chronic C2 hypertrophic ganglioneuritis in a Yorkshire Terrier has been published, and MRI findings for that dog shared similarities with findings for the dog of the present report. In that dog,2 surgical treatment (durotomy and C2 rhizotomy) resulted in a favorable outcome.

To conclude, in dogs, spinal nerve neoplasia and hypertrophic ganglioneuritis may be difficult to discriminate solely on the basis of signalment, clinical signs, MRI findings, and results of CSF analysis. Cytologic and, ideally, histologic examination should be performed in these cases to distinguish between inflammatory and neoplastic spinal radiculopathies, because outcomes differ substantially. The present report represents the first reported case of a spinal nerve root neurofibroma in a dog with a description of MRI findings; it serves as a reminder that focal spinal nerve enlargement in dogs may have a malignant cause, such as neurofibroma, and that the prognosis may not be favorable with either medical or surgical management.

References

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