A 4-year-old 12.8-kg (28.2-lb) castrated male Miniature Schnauzer was evaluated because of sudden-onset paraplegia. The owners first noticed a decline in the dog's activity level approximately 1 week prior. At that time, the dog was examined by the primary veterinarian, who reported no ataxia or neurologic deficits. Clinicopathologic and abdominal radiographic findings were interpreted as unremarkable. The dog was treated with an SC injection of maropitant citrate (13 mg) once, tramadol hydrochloride (50 mg, PO, q 12 h for 1 week), and carprofen (25 mg, PO, q 12 h for 1 week). Despite these treatments, the dog progressed from being fully ambulatory to dragging both hind limbs over the course of 1 week. The dog was described as nonambulatory for a total of 3 days prior to the referral evaluation.
Neurologic examination revealed the dog was nonambulatory with bilateral pelvic limb plegia and complete loss of pelvic limb conscious proprioception. Conscious proprioceptive reactions were normal in the thoracic limbs. Marked thoracolumbar hyperesthesia was elicited on vertebral column palpation, as well as mild cervical hyperesthesia during deep cervical palpation. Segmental reflexes were consistent with an upper motor neuron localization. No other abnormalities were detected during general physical examination.
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
| Problem | Rule out location |
|---|---|
| Paraplegia with deep nociception and corresponding thoracolumbar hyperesthesia | T3-L3 myelopathy (possibly multifocal) |
| Mild cervical hyperesthesia | C1–C5 myelopathy (possibly multifocal) |
Likely location of 1 lesion
Myelopathy at the region of the vertebral column from T3 through L3
Etiologic diagnosis—Differential diagnoses for an acute, progressive paraplegia originating in the thoracolumbar portion of the vertebral column include intervertebral disk disease (Hansen type I disk extrusion most likely), inflammatory disease, infectious diseases (eg, bacterial, viral, or protozoal infection), diskospondylitis, and neoplasia (primary or metastatic). Given this dog's signalment, signs of pain on vertebral palpation, and the acute, progressive nature of the pelvic limb plegia, intervertebral disk disease was highly suspected. The presence of a multifocal disease process could not be excluded, however, given the signs of cervical pain on examination (eg, multiple sites of disk herniation or infectious or inflammatory disease). Recommended diagnostic testing for this dog included a CBC and serum biochemical analyses (to obtain a general health profile), and MRI of the thoracolumbar portion of the vertebral column (to detect structural abnormalities). If MRI failed to identify the cause of clinical signs or if a nonsurgical lesion was identified, then analysis of a sample of CSF would be indicated (to further evaluate for an inflammatory, infectious, or neoplastic cause).
Diagnostic test findings—Results of the CBC were within reference intervals except for mild hemoconcentration (Hct, 57.3%; reference interval, 38.3% to 56.5%). Serum biochemical abnormalities included high concentrations of sodium (156 mmol/L; reference interval, 142 to 152 mmol/L) and triglycerides (445 mg/dL; reference interval, 20 to 150 mg/dL) and high activity of corticosteroid-induced alkaline phosphatase (56 U/L; reference interval, 0 to 35 U/L). Thoracolumbar MRIa was performed. Sagittal and axial T1-weighted fast spin echo sequences, sagittal and axial T2-weighted fast spin echo sequences, and a sagittal short tau inversion recovery sequence without contrast medium administration were obtained. After contrast medium administration, sagittal, axial, and dorsal T1-weighted fat suppression sequences were obtained. Magnetic resonance imaging revealed an intradural, extramedullary, strongly homogeneous contrast-enhancing lesion with variable spinal cord compression between the T8 and L1 vertebral segments (Figure 1). Spinal cord compression from this contrast-enhancing lesion was most severe along the dorsal margins of the T9 to T13 vertebral segments. There was continuity of this lesion with the dural meninges and marked circumferential contrast enhancement of the meninges both cranial and caudal to the lesion.
Magnetic resonance images of the thoracolumbar region of the vertebral column of a 4-year-old dog that was evaluated because of progressive sudden-onset pelvic limb plegia. A—A T1-weighted fat suppression sagittal image obtained after contrast medium administration. Notice the homogeneous contrast-enhancing lesion (white arrows) extending from the level of the T8 through the L1 vertebra. The lesion is intradural, extramedullary, and mostly dorsal in location causing marked dorsal spinal cord compression. There is extensive, marked contrast enhancement of the surrounding meninges, which appear continuous with the compressive lesion. B—A T1-weighted fat suppression axial image obtained after contrast medium administration. The intradural extramedullary lesion occupies approximately 75% of the neural canal (white arrow) at the level of the T12 vertebra with ventral displacement of the spinal cord. Patchy contrast enhancement is visible in the epaxial muscles.
Citation: Journal of the American Veterinary Medical Association 251, 5; 10.2460/javma.251.5.511
Following review of the MRI findings, a CSF sample was obtained, and analysis revealed a high total protein concentration (52.1 mg/dL; reference interval, ≤ 25 mg/dL) with a normal nucleated cell count (3 cells/μL; reference interval, 0 to 4 cells/μL). Most cells were small, well-differentiated lymphocytes; no overtly neoplastic or infectious agents were detected. Differential diagnoses at that time included a neoplastic process and infectious disease (eg, fungal infection). Thoracic radiography and abdominal ultrasonography were performed the day after MRI, and no important abnormalities were identified.
Comments
Following the completion of the diagnostic workup, a definitive diagnosis could not be made; however, there was a strong suspicion for a neoplasm localized to the spinal cord. Multiple treatment options were discussed with the client, including collection and examination of a biopsy specimen of the lesion to direct disease-specific treatment, palliative treatment for presumed round cell neoplasia, or euthanasia if treatment was not to be elected. The clients decided to proceed with biopsy in the hope of obtaining a definitive diagnosis. A biopsy specimen of the lesion was obtained by performing a left-sided pediculectomy and durotomy at the level of the T12 vertebra. Microscopic examination of impression smears of the lesion revealed a homogeneous population of highly anaplastic round cells, with the primary differential diagnosis being histiocytic sarcoma. Histologic examination of the biopsy specimen, with the aid of immunohistochemical analysis, confirmed the diagnosis of histiocytic sarcoma. Approximately 95% of the neoplastic population was positive for CD18 and diffusely negative for multiple myeloma oncogene-1 (MUM1). Chemotherapy with lomustine was proposed as the treatment option of choice to the clients, but was declined. The dog was euthanized approximately 5 days following discharge from the hospital.
Histiocytic sarcoma is a malignant tumor type that originates from either dendritic or macrophage cell lineage.1 Histiocytic sarcoma can be either a localized lesion or disseminated throughout multiple organ systems. Anatomic sites at which histiocytic sarcomas have been reported include the spleen, liver, lymph nodes, lungs, and joints.1–3 Histiocytic sarcoma localized to the CNS, and specifically to the spinal cord, is uncommonly diagnosed.4 Spinal cord histiocytic sarcoma is presumed to originate from malignant transformation of dendritic cells located within the meninges.1,5 As a result, profound meningeal enhancement and continuity of the neoplastic lesion with the meningeal lining of the spinal cord are common MRI findings.4,6 Each of these characteristics were identified in the case described in the present report. Aside from meningeal enhancement, spinal cord histiocytic sarcoma characterization can be variable. Both solitary and multifocal lesions have been described, as well as intradural extramedullary lesions and intramedullary lesions.4,6 Owing to the variability of MRI findings in cases of spinal cord histiocytic sarcoma, it can be challenging to differentiate these lesions from other forms of spinal cord neoplasia (eg, lymphoma or meningioma) with imaging techniques alone. The dog of the present report had an intradural, extramedullary compressive thoracolumbar lesion, but may have had additional lesions in other spinal cord segments that were not identified. Signs of cervical pain were evident on physical examination, and it remains unknown whether the signs of pain were attributable to meningitis associated with the thoracolumbar lesion or representative of additional lesions affecting the cervical portion of the spinal cord.
Cerebral spinal fluid analysis was performed in the case described in the present report to aid with diagnosis. The results of CSF analysis in dogs with spinal cord histiocytic sarcoma have been previously described, with pleocytosis and high total protein concentration reported as common findings.4 Findings for the dog of the present report (ie, high total protein concentration with a normal nucleated cell count) were inconsistent with these previous descriptions; no neoplastic cells were identified on cytologic examination of the CSF sample, which is typical in cases of spinal cord histiocytic sarcoma.4
Unfortunately, prognosis is poor for dogs with spinal cord histiocytic sarcoma, with a reported median survival time of only 3 days following diagnosis.4 Histiocytic sarcoma lesions amenable to local treatment (eg, surgery) in combination with adjuvant chemotherapy, such as periarticular histiocytic sarcoma, are generally associated with longer survival times2; however, the anatomic location of spinal cord histiocytic sarcoma often precludes resection of affected tissue. Lomustine chemotherapy was recommended for the dog of the present report. Lomustine chemotherapy is reported to have an overall response rate of 46% in dogs with gross or disseminated histiocytic sarcoma,7 but survival time is still limited in those dogs that achieve either a partial or complete response. In the case described in the present report, the owners declined chemotherapy because of the dog's poor prognosis and instead elected euthanasia.
Spinal cord histiocytic sarcoma is an atypical cause of thoracolumbar spinal cord compression and pelvic limb plegia. Dogs affected by this disease have clinical signs similar to those associated with other thoracolumbar myelopathies, with variable degrees of pain and neurologic deficits. Findings of advanced imaging techniques and CSF analysis can be useful when evaluating these lesions, although histologic examination of affected tissue may be required to make the definitive diagnosis. Presently, there is limited information available regarding the ideal treatment for spinal cord histiocytic sarcoma and the overall prognosis for affected dogs is considered poor.
Acknowledgments
The authors declare no financial support or conflicts of interest with respect to the authorship or publication of this article.
Footnotes
1.5-T GE Signa Echospeed Plus, GE Healthcare, Milwaukee, Wis.
References
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3. Fulmer AK, Mauldin GE. Canine histiocytic neoplasia: an overview. Can Vet J 2007; 48: 1041–1050.
4. Mariani CL, Jennings MK, Olby NJ, et al. Histiocytic sarcoma with the central nervous system involvement in dogs: 19 cases (2006–2012). J Vet Intern Med 2015; 29: 607–613.
5. Uchida K, Morozumi M, Yamaguchi R, et al. Diffuse leptomeningeal malignant histiocytosis in the brain and spinal cord of a Tibetan Terrier. Vet Pathol 2001; 38: 219–222.
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7. Skorupski KA, Clifford CA, Paoloni MC, et al. CCNU for the treatment of dogs with histiocytic sarcoma. J Vet Intern Med 2007; 21: 121–126.
