What Is Your Diagnosis?

Shayna M. Streu From the Department of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, MO 65211.

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Ian R. Porter From the Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853.

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Aitor Gallastegui Menoyo From the Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610.

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History

A 3-year-old 44.7-kg spayed female Boxer was referred for evaluation because of acute hind limb weakness, difficulty walking, and hyporexia. The owners reported initially noticing that the dog appeared uncomfortable when getting up from lying down and that the dog seemed unsteady on its hind limbs when standing. The referring veterinarian had initiated treatment with deracoxib (1.7 mg/kg, PO, q 24 h) for signs of pain and cephalexin (11.2 mg/kg, PO, q 12 h) for a concurrent dermatologic infection. The dog had progressive weakness and 3 days later was referred for further evaluation.

On referral examination, the dog was bright, alert, and responsive. Results of a CBC and serum biochemical analyses indicated mild neutrophilia (14,700 neutrophils/µL; reference range, 5,700 to 9,400 neutrophils/µL) and high serum creatine kinase activity (12,494 U/L; reference range, 48 to 261 U/L). Neurologic examination revealed no abnormalities in the cranial nerves or in mentation, but paraparesis with loss of conscious proprioception in the hind limbs, and mildly exaggerated patellar reflexes were present. Muscle atrophy was not detected, and no abnormalities were identified in the forelimbs. Signs of mild discomfort were elicited on deep palpation of the back between T3 and L3. On the basis of these findings, myelopathy between T3 and L3 was prioritized, and a radiographic examination of the vertebral column between T3 and L3 was performed (Figure 1).

Figure 1
Figure 1
Figure 1
Figure 1

Right lateral (A and B) and ventrodorsal (C) radiographic images of the thoracolumbar portion of the vertebral column of a 3-year-old 44.7-kg spayed female Boxer with acute hind limb weakness, difficulty walking, and hyporexia.

Citation: Journal of the American Veterinary Medical Association 259, 11; 10.2460/javma.19.10.0527

Formulate differential diagnoses, then continue reading.

Diagnostic Imaging Findings and Interpretation

The dog had multifocal aggressive bone lesions of the vertebral column, with a large amount of continuous, smooth, bridging new bone formation along the ventral aspect of the vertebral bodies from T8 to S1 (Figure 2). The vertebral body of L2 had a large, ill-defined lucency that extended ventrally into the bridging new bone formation. The L3 spinous process had moderate moth-eaten lysis. The laminae and pedicles of L4 and the lamina of L5 had less opacity and ill-defined margins. The ventral bridging new bone formation had a region of increased lucency that spanned T10-T13. In addition, the wing of the right ilium was lytic and had ill-defined cranial cortical margins. Our primary differential diagnosis for the aggressive bone lesions was neoplasia, such as lymphoma or multiple myeloma.

Figure 2
Figure 2
Figure 2
Figure 2

Same images as in Figure 1. The vertebral column, from T8 (arrows) to S1 (arrowhead), has evidence of a large amount of flowing, continuous, smooth, ventral, bridging new bone formation, best seen in the right lateral images (A and B), and a region of increased lucency (white dotted-outline oval) that spans T10-T13. Regions of ill-defined vertebral lysis (white solid-outline circles and ovals) are seen in the L2 vertebral body, L3 spinous process, L4 laminae and pedicles, and L5 lamina. The wing of the right ilium is lytic (black dotted-outline circle). In the more cranial lateral image (B), an abnormal soft tissue opacity (black arc) is evident in the cranioventral aspect of the thorax.

Citation: Journal of the American Veterinary Medical Association 259, 11; 10.2460/javma.19.10.0527

No abnormality was evident in the intervertebral disk spaces or vertebral endplates. However, the joints between the articular processes of the lumbar vertebrae had medium-sized osteophytes, which were degenerative changes consistent with diffuse idiopathic skeletal hyperostosis (DISH).

In the cranioventral aspect of the thorax, there was a rounded soft tissue opacity that extended beyond the edge of the lateral image. Although our orthogonal image did not include this more cranial site and, thus, this soft tissue opacity could not be localized (eg, to the mediastinum, lung, or body wall), we suspected a cranial mediastinal mass attributable to neoplasia, such as lymphoma with lymphadenopathy or thymic lymphoma with a thymic mass.

The dog underwent general anesthesia for MRI of the vertebral column (Figure 3). The aggressive bone lesions were confirmed and included the body and spinous process of T12, part of the spinous process of T13, the body of L2 with extension into the ventral bridging new bone formation and into the ventral aspects of L1 and L3, the spinous process of L3, the laminae, pedicles, articular processes, and vertebral body of L4, the lamina, pedicles, and articular processes of L5, the wing of the right ilium, and body of the left ilium. At the level of L4, the bone lesion was moderately expansile and extended into the vertebral canal, causing moderate, focal, ventral displacement and compression of the spinal cord. The DISH lesions and the ventral bridging new bone formation detected on radiography were also identified on MRI. However, the area of increased radiographic lucency surrounded by compact bone in the ventral bridging new bone formation between T10 and T13 appeared on MRI to have been a region of marrow within the DISH lesion. On the basis of these findings, the dog’s paraparesis was attributed to myelopathy secondary to spinal compression at L4; the differential diagnosis remained unchanged.

Figure 3
Figure 3
Figure 3
Figure 3
Figure 3

Sagittal plane precontrast T2-weighted (A), STIR (B), and T1-weighted (C) and postcontrast T1-weighted, fat-saturation (D) MRI images of the thoracolumbar region (T12 [black arrows] to S1 [black arrowheads]) of the vertebral column of the dog described in Figure 1. At the level of L4, there is moderate focal narrowing of the vertebral canal and ventral displacement and compression of the spinal cord (white arrows). Vertebral lesions (asterisks) are hyperintense on the T2-weighted and STIR images, are hypointense on the precontrast T1-weighted image, and show contrast enhancement on the postcontrast T1-weighted, fat-saturation image. In all images, cranial is toward the left and dorsal is toward the top.

Citation: Journal of the American Veterinary Medical Association 259, 11; 10.2460/javma.19.10.0527

Treatment and Outcome

Ultrasound-guided fine-needle aspirate samples of the spinous process of L3 were obtained, and cytologic results were consistent with intermediate to large-cell lymphoma. Given the dog’s clinical signs and prognosis and the owners’ concern for the dog’s quality of life, the owners elected euthanasia for the dog.

Comments

For the dog of the present report, vertebral lesions identified radiographically and on MRI were cytologically diagnosed as intermediate to large-cell lymphoma. Lymphoma is one of the most common types of neoplasms affecting dogs; however, descriptions of advanced imaging of vertebral lymphoma are rare. Two recent reports1,2 describe MRI features of lymphoma in the vertebral column, with MRI characteristics including lesions that are isointense to mildly hypointense on T1-weighted images, isointense or hyperintense on T2-weighted images, hyperintense on STIR images, and have moderate to strong contrast enhancement. Additionally, vertebral lymphoma lesions are centered in the medullary cavity, reflecting the replacement of medullary bone marrow fat with malignant cellular infiltrate.1,2 Our findings on MRI for the dog of the present report were consistent with these previously described characteristics of vertebral lymphoma.

Additionally, this dog had radiographic and MRI evidence of DISH, which is a systemic disease that affects the axial and appendicular skeleton in people and dogs, often occurring in dogs as young as 2 years of age.3 Although debate over radiographic criteria for the diagnosis of DISH3,4,5,6 exists, the dog of the present report had radiographic evidence that satisfied sufficient criteria for diagnosis of DISH, including the presence of bridging ossification along the ventrolateral aspect of ≥ 4 contiguous vertebral bodies, preservation of intervertebral disk space width in the involved vertebral segment, and absence of radiographic changes of degenerative disk disease (eg, endplate sclerosis, nuclear calcification, or localized spondylosis deformans).

A more recent study7 looked at the MRI characteristics of DISH and compared them with MRI characteristics of spondylosis deformans. In spondylosis deformans, new bone formation has low signal intensity on T1- and T2-weighted images when compared with the signal intensity of normal vertebral bone marrow, and in many cases, this hypointense signal extends into the area of the vertebral endplates, consistent with bone sclerosis.7 In DISH, new bone formation contains marrow that has high signal intensity on T1- and T2-weighted images and suppressed signal intensity in STIR images, similar to normal vertebral bone marrow. Our findings for areas of the involved vertebrae not affected by lymphoma in the dog of the present report displayed characteristics of bone marrow, which was consistent with DISH.

For the dog of the present report, radiographic evidence was highly suggestive of infiltrative neoplasia, and given the cytologic findings for samples obtained from ultrasound-guided fine-needle aspiration of the spinous process of L3, MRI was not required for diagnosis. However, MRI was elected to further characterize the extent and severity of disease. The MRI results supported the diagnosis of infiltrative neoplasia, definitively identified the cause of myelopathy (spinal cord compression at the level of L4), and provided information needed by the owners in their deliberation on further treatment of their dog. In patients with less advanced vertebral lymphoma for which radiographic lesions are not evident, MRI may be a more sensitive diagnostic procedure. Findings for the dog of the present report highlighted diagnostic imaging features of an unusual presentation of a common disease: polyostotic vertebral lymphoma with extension into the bone marrow of a DISH lesion.

References

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