Intravascular Lymphoma Involving the Central and Peripheral Nervous Systems in a Dog

Case Report

A 5-year-old, castrated male mixed-breed dog was referred to the neurology service of the Veterinary Hospital of the University of Pennsylvania (VHUP) for evaluation of a 5-month history of progressive pelvic-limb ataxia, paraparesis, neck and back pain, and thrombocytopenia. Seizures, lethargy, and anorexia were present for 2 weeks prior to presentation. The dog’s vaccinations were current for distemper, adeno-virus-2, leptospira, parainfluenza, parvovirus, and rabies. The dog had a history of traveling throughout the New England area. Initially, the clinical signs and thrombocytopenia resolved with 7 days of prednisone therapy (0.5 mg/kg body weight, per os [PO] q 24 hours). However, attempts at discontinuing or decreasing the dose resulted in recurrence of clinical signs. Consequently, the patient had received steroids intermittently for 3 months and then consistently for the last month prior to admission to VHUP.

The general physical examination showed a mild elevation in the respiratory rate and effort. Neurological examination showed normal mental status but inability to ambulate due to pelvic-limb paresis, ataxia, and severe postural deficits (i.e., replacement of knuckled paw, hopping, placing) in both pelvic limbs, with the right limb worse than the left. Cranial nerve examination showed lack of a menace response in the left eye, lack of direct or consensual pupillary light reflexes in the left eye, and decreased sensation in the left nostril. Fast-phase right horizontal nystagmus was present when the dog was placed in dorsal recumbency. There was severe hyperesthesia with palpation of the spinal epaxial musculature over the neck and back. Indirect ophthalmoscopy showed tortuous retinal vessels in the tapetal fundus that were worse in the left eye, and scleral hemorrhage in the right eye. Multifocal neurological disease was suspected. Differential diagnoses included infectious (i.e., toxoplasmosis, neosporosis, cryptococcosis, canine distemper, rickettsial, bacterial), inflammatory (i.e., granulomatous meningoencephalomyelitis [GME]), and neoplastic diseases.

Abnormalities detected in the complete blood count (CBC) included thrombocytopenia (44 × 10³/μL; reference range, 176 to 400 × 10³/μL) and nonregenerative normocytic, normochromic anemia (hematocrit, 29.6%; reference range, 40.3% to 60.3%; red blood cell count [RBC], 4.0 × 10⁶/μL; reference range, 5.83 to 8.87 × 10⁶/μL). The absolute reticulocyte count was 40,000/μL. Plasma total protein was 6.0 gm/dL (reference range, 6.0 to 8.0 gm/dL). Bone-marrow aspiration and cytopathology revealed a slightly increased myeloid to erythroid ratio of 2.7:1. This data was interpreted as mild erythroid hypoplasia, compatible with an anemia secondary to chronic disease. A direct Coombs’ test and antinuclear antibody test performed a few days prior to presentation were both negative.

Serum biochemistry abnormalities included a mild increase in alanine aminotransferase (161 U/L; reference range, 16 to 91 U/L), alkaline phosphatase (293 U/L; reference range, 24 to 174 U/L), and gamma-glutamyltransferase (30 U/L; reference range, 7 to 24 U/L) considered compatible with corticosteroid administration. Results of serological tests for Neospora caninum and Toxoplasma gondi were negative. Serology for Ehrlichia canis and Rickettsia rickettsii, performed 3 months prior to presentation and at presentation, were both negative. Serology for canine distemper virus was 1:1445 in the serum and 1:192 in the cerebrospinal fluid (CSF); this was likely due to the patient vaccination history. Cryptococcus neoformans antigen agglutination testing performed on CSF was negative. Arterial blood gas analysis demonstrated low normal oxygen and carbon dioxide concentrations (PaO₂, 83 mm Hg; reference range, 80 to 100 mm Hg; PaCO₂, 34 mm Hg; reference range, 35 to 45 mm Hg) but an elevated alveolar-arterial oxygen gradient (24.5 mm Hg; reference range, <20 mm Hg). Thoracic radiography revealed a mild interstitial pattern consistent with atelectasis or pneumonitis.

One day after admission, CSF was collected from the cerebellomedullary cistern and immediately analyzed. Abnormalities included xanthochromia, an elevated total protein (1,343 mg/dL; reference range, <25 mg/dL), positive Pandy test, elevated RBC (120,135 cells/μL), and elevated nucleated cell count (563 cells/μL; reference range, <5 cells/μL). Cytocentrifuged smears contained 44% non-degenerate neutrophils, 52% small lymphocytes, and 4% macrophages, with occasional erythrophagocytosis. The analysis was consistent with hemorrhage into the CSF and probable inflammation. Aerobic culture of the CSF was negative for growth.

Prednisone (1 mg/kg body weight, PO q 12 hours) was initiated for its anti-inflammatory and immune-modulating properties, and sucralfate (40 mg/kg body weight, PO q 6 hours) and ranitidine (2 mg/kg body weight, PO q 12 hours) were administered to protect the gastrointestinal tract from the effects of the steroid therapy. Fentanyl (100 μg per hour, transdermal) was administered for the hyperesthesia. Due to a concern that an infectious etiology may have evaded detection, therapy was initiated with sulfamethoxazole and trimethoprim (15 mg/kg body weight, PO q 12 hours), clindamycin (10 mg/kg body weight, PO q 12 hours), and doxycycline (10 mg/kg body weight, PO q 24 hours).

Three days after admission, there was no improvement in the patient’s neurological status, and magnetic resonance imaging (MRI) of the brain and cervical spinal cord was performed. Lesions were revealed in the brain stem, cerebellum, cerebral hemispheres, right lateral ventricle, spinal cord, and meninges. The lesions involved both the white and gray matter and were hyperintense on T2-weighted images [Figure 1]. Immediately after the administration of gadolinium^a (0.3 mL/kg body weight, intravenously [IV]), there was strong enhancement of the meninges and right temporal lobe and mild enhancement of the right lateral ventricle [Figure 2]. The hyperintensity with T2-weighting and enhancement after the administration of gadolinium suggested encephalitis and ventriculitis. Differentials for these findings included infectious/inflammatory disease and round cell neoplasia.

Three days after admission, the patient developed a significant increase in the respiratory rate and effort. Arterial blood gas analysis demonstrated hypoxemia (PaO₂, 66 mm Hg; reference range, 80 to 100 mm Hg) and hypocapnia (PaCO₂, 32 mm Hg; reference range, 35 to 45 mm Hg), with a more significant elevation in the alveolar-arterial gradient (44 mm Hg; reference range, <20 mm Hg). Thoracic radiography revealed a suspect bronchopneumonia in the right middle and left cranial lung lobes; this was confirmed via cytological evaluation of a transtracheal wash, which indicated suppurative inflammation secondary to a bacterial infection. Although no regurgitation or vomiting was noted, the clinical diagnosis based on the radiographs and cytology results was aspiration pneumonia. Culture of the transtracheal fluid identified Escherichia coli. The dog was treated with nebulization and coupage (q 4 hours), amino-phylline (10 mg/kg body weight, IV q 8 hours), and specific antimicrobial therapy with cefotaxime (20 mg/kg body weight, IV q 12 hours). The patient’s respiratory rate and effort improved substantially over the next 2 days. However, the alveolar-arterial gradient remained elevated.

One week after admission, there was no improvement in the neurological status of the patient. A computed tomography (CT) scan of the brain was performed in order to plan for a CT-guided biopsy. The patient was given oxymorphone (0.05 mg/kg body weight, IV), diazepam (0.3 mg/kg body weight, IV), and lidocaine (2 mg/kg body weight, IV), followed by thiopental (4 mg/kg body weight, IV) for the induction of anesthesia and was maintained with isoflurane inhalation anesthesia. The CT scan of the brain revealed an ill-defined, multifocal parenchymal and diffuse meningeal enhancement immediately after the administration of contrast (diatrizoate meglumine and diatrizoate sodium,^b 0.5 mg/kg body weight, IV). The precontrast images of the brain revealed no abnormalities. Using the MRI and the postcontrast CT scan to plan the biopsy procedure and a head holder designed by one of the authors (Vite), a CT-guided biopsy was obtained from the right temporal lobe. The head holder was made out of the polymer lexan and designed after the metal Kopf head holder (model 1530).^c The other two parts of the biopsy equipment, the frame and the electrode manipulator, were made by Kopf Instruments.^d The postcontrast CT scan was used to take measurements relative to the head holder, and three coordinates (i.e., width, length, depth) were set in order to determine the anatomical location of the biopsy (ectosylvian gyrus/temporal lobe) [Figure 3]. Access to the central nervous system was gained via a surgical incision through the temporalis muscle followed by the use of a 3M mini drill with a bit and guard to drill a hole through the calvarium. A CT scan, done while the biopsy needle was in place, confirmed that the needle was in the correct anatomical location. Three biopsies were taken from the same site at slightly different depths using a Nashold biopsy needle.^e A CT scan, performed after the biopsy needle was removed, did not demonstrate any bleeding. Recovery from the anesthesia was unremarkable, and the patient returned to the same neurological status 12 hours after the procedure. Cytopathological smears made from the samples of the ectosylvian gyrus/temporal lobe of the brain contained many lymphocytes, moderate numbers of neutrophils, few macrophages, and a large amount of neural tissue. Most of the lymphocytes were small and morphologically unremarkable; however, a few clusters of moderately large to very large lymphoblasts were embedded within the neural tissue [Figure 4]. These immature lymphocytes suggested a neoplastic population of cells, but their numbers were too few to allow a definitive cytopathological interpretation. Prior to the CT-guided biopsy, but during the same anesthetic episode, CSF was again sampled from the cerebellomedullary cistern. Analysis demonstrated a mixed-cell pleocytosis and hemorrhage was identified, but atypical lymphocytes were not detected. The total protein was elevated (1,384 mg/dL), but the nucleated cell and RBC counts had decreased (80/μL and 1,350/μL, respectively). Fifty-four percent small lymphocytes, 45% neutrophils, and 1% macrophages were found. Occasional erythrophagocytosis was observed.

Histopathological examination of the biopsies of the right temporal lobe showed a mild increase in the number of glial cells surrounding the neurons and a few blood vessels that contained large cells of the lymphoid series. Some of the blood vessels had slightly hypertrophied endothelial cells. The presence of pleomorphic round cells in some of the vessels was suggestive of intravascular lymphoma [Figure 5].

Eight days after admission, a second episode of aspiration pneumonia was confirmed with thoracic radiography; treatment was initiated with amikacin (15 mg/kg body weight, IV q 24 hours). Once again, the patient was not observed to vomit or regurgitate, but neurological disease and anesthesia are known risk factors for the development of aspiration pneumonia.¹ Radiographic resolution of the aspiration pneumonia was achieved in 2 days. Despite this, hypoxemia and the alveolar-arterial gradient did not improve. Persistent hypoxemia and an elevated alveolar-arterial gradient with normal chest radiography prompted a tentative diagnosis of pulmonary thromboembolism. Antithrombin III activity was slightly decreased at 62% (reference range, 75% to 120%). Coagulation profiles showed an 11% and 9% decrease in the prothrombin time and partial thromboplastin time [PTT], respectively, versus controls. Intravenous heparin treatment was started at a constant-rate infusion (40 units/kg body weight per hour) with a goal of a PTT that was one and a half times normal. The heparin dose was later increased to 60 units/kg body weight per hour, resulting in an appropriate prolongation of the PTT.

Eight days after admission, chemotherapy was initiated with L-asparaginase^f (10,000 IU, subcutaneously [SC]), followed by vincristine^g (0.5 mg/m², IV) 3 days later. In humans with intravascular lymphoma, chemotherapy is recommended, as more than half the patients receiving cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) respond with complete remission.² This patient was debilitated with pneumonia at the time of diagnosis, and L-asparaginase and vincristine were selected from the CHOP protocol since they are recommended in many protocols for dogs with lymphoma and are nonmyelosuppressive.³

Nine days after admission, continuous electrocardiographic monitoring revealed accelerated idioventricular rhythms and moderate ventricular tachycardia (150 beats per minute). Continuous direct blood pressure monitoring revealed periods of hypertension (systolic pressure spikes of >200 mm Hg) with mean arterial pressures up to 135 mm Hg. Generally, systolic pressures averaging 140 mm Hg, with mean arterial pressures averaging about 100 mm Hg, were recorded. Additionally, a mild hyperkeratotic crust developed on the dorsal nasal planum. The distal pelvic limbs had ecchymosis and well-circumscribed erosive lesions. Differential diagnoses for the skin lesions included systemic lupus erythematosus and vasculopathy.

Twelve days after admission, the patient developed intermittent dullness, paraplegia, crossed-extension response in the pelvic limbs, increased patella reflexes, and a tendency to turn to the left when supported to walk. Fourteen days after admission, the patient developed a decreased perineal reflex, poor anal tone, a decreased gag reflex, a decreased withdrawal reflex in the right pelvic limb, decreased sensation in the right nostril, decreased tear production in both eyes, and a ventral strabismus in the right eye. These findings suggested worsening of disease with involvement of the lumbar intumescence or the cauda equina, prosenecephalon, brain stem, and spinal cord. The changes in the neurological examination were not believed to result from the biopsy or chemotherapy.

Due to the progression of neurological signs, the patient was euthanized 2 weeks after admission to VHUP. Cerebrospinal fluid was collected from the cerebellomedullary cistern just after euthanasia and was analyzed immediately. The fluid was pale yellow, with a total protein of 1,072 mg/dL, 2 nucleated cells/μL, and 88 RBC/μL. Two cytocentrifuged smears contained 39 small, morphologically unremarkable lymphocytes; 13 nondegenerate neutrophils; nine macrophages; and RBCs. Immature lymphocytes were not detected.

Gross inspection of the spinal cord revealed a brown discoloration in the caudal meninges. When the dura over the cervical spinal cord and lumbar intumescence was incised, prominent subdural vessels were seen [Figure 6]. These prominent, congested vessels were suspected to be a result of occlusion by nests of neoplastic cells. Histopathology of the spinal cord identified intravascular lymphoma with thrombi, hemorrhage, and multifocal, fibrinoid, vascular necrosis (i.e., infarcts). Histopathology of the brain demonstrated thrombi, hemorrhage, and multifocal, fibrinoid, vascular necrosis (i.e., infarcts) with cavitation of the internal capsule. Histopathology of the eyes also revealed intravascular lymphoma. This was a likely cause for the blindness in the left eye and the tortuous retinal vessels. Intravascular lymphoma was found in the lung and was the likely cause of the arterial blood gas abnormalities. Intravascular lymphoma was found in the heart in addition to severe myocardial necrosis (i.e., infarcts), multifocal fibrinoid necrosis of the coronary arteries, smooth muscle hypertrophy, thrombi, and intramural hemorrhage. The cauda equina, optic and pudendal nerves, pancreas, and adrenal gland were also affected. Changes in the skin were consistent with a vasculopathy. There was no bone-marrow involvement.

The neoplastic cells were strongly positive for CD45RA antigen (B-cell, T-cell, monocyte marker) and infrequently positive for CD3 antigen (a T-cell marker). The neoplastic cells also stained negative for MAC387, Alpha D, and CD18 (monocyte/macrophage markers); BLA36 and CD79a (B-cell markers); AE1/AE3 (cytokeratin); and GFAP (astrocyte marker, used as an internal positive control). This staining pattern is most consistent with a diagnosis of T-cell lymphoma,⁴ as the cells stained positive for a T-cell marker and negative for monocyte and B-cell markers.

Discussion

Intravascular lymphoma is a proliferation of neoplastic lymphocytes within the lumen and wall of blood vessels. The progressive occlusion of blood vessels with neoplastic cells leads to thrombosis, hemorrhage, and infarction.⁵ Multiple case reports and one large case series of intravascular lymphoma in dogs,^5–8 as well as one report in a cat,⁹ have been published. Similar to the patient of this study, intravascular lymphoma is most common in middle-aged, large-breed dogs.⁸ The disease in dogs and humans has a propensity for the central nervous system and lungs.⁸ The progression is rapid, and death occurs within 20 days to 6 months of the first clinical signs in dogs and 1 to 13 months in humans.^5–710–12

In the dog described in this paper, multifocal neurological disease and ophthalmological, pulmonary, cardiac, and hematological diseases suggested an infectious, inflammatory, or neoplastic process. Since the bone-marrow examination was normal, this patient’s thrombocytopenia was postulated to be secondary to consumption of platelets by thrombi within diseased vessels. Intravascular lymphoma has not been described to involve the bone marrow in either dogs or humans.⁸¹⁰ Also, similar to humans, peripheral blood smears did not demonstrate neoplastic cells.⁸ The elevations in protein and cells in the CSF suggested inflammatory nervous system disease but were nonspecific. The CSF sample collected at the end of therapy had a lower nucleated cell count and was most similar to the CSF findings in other veterinary and human reports.⁷¹³ The CSF findings of this case reflect the range of abnormalities that may occur with this disease or they may reflect the influence of chemotherapy. Negative titers for infectious agents, the negative CSF culture, and the lack of a response to antimicrobial therapy supported a neoplastic or inflammatory process.

The MRI demonstrated significant contrast enhancement of the meninges, ventricular walls, and brain parenchyma as well as hyperintensity on T2-weighted images of multiple regions in the brain, spinal cord, and periventricular areas. The gadolinium-enhanced T1-weighted images demonstrated areas of significant enhancement. Postcontrast CT images showed multifocal areas of parenchymal enhancement and diffuse meningeal contrast enhancement. Neither imaging modality provided a specific diagnosis. The enhancing regions were selected for biopsy via CT guidance. The CT-guided brain biopsy proved to be a safe and useful method for acquiring tissue for a specific diagnosis, as both cytopathology and histopathology strongly suggested intravascular lymphoma. On cytopathology, clusters of immature lymphocytes were identified, while histopathology demonstrated pleomorphic round cells in the vessel lumen and endothelial hypertrophy. Although the skin lesions in this instance were not associated with intravascular lymphoma, vigilance for skin lesions for biopsy may also be worthwhile, as one dog has been diagnosed via skin biopsy.⁸ In humans, biopsies of the brain, skin, muscle, bronchiole, adrenal glands, and kidney, as well as brain MRI, can be useful for diagnosis.^2111314

The necropsy findings in this dog are similar to those reported for other dogs with intravascular lymphoma.⁸ Histopathological examination demonstrated that multiple organ systems (i.e., pulmonary, nervous, ophthalmological, gastrointestinal, endocrine, cardiac) were affected. Retinal vessels contained intravascular lymphoma cells. No retinal detachment was found, although this has been reported to occur.⁵¹² Cauda equina involvement was found in this dog, as has been reported in human patients.¹⁵ Additionally, severe myocardial and coronary artery diseases were found, although they were more severe than previous reports indicated.⁸ These additional changes in the heart may have been related to the long clinical course in this patient. Similar to other veterinary reports, immunohistochemistry suggested the neoplasm might have been a T-cell lymphoma.⁸ Interestingly, the most common intravascular lymphoma in humans is a B-cell neoplasia.²

In human patients with intravascular lymphoma, chemotherapy with CHOP has shown efficacy.¹³¹⁴ In fact, many patients achieved long-term disease-free survival and occasionally complete remission.^213–15 In this patient, the clinical signs and thrombocytopenia responded to intermittent prednisone therapy for about 4 months. Late in the disease, the addition of L-asparaginase and vincristine to the prednisone therapy did not appear to alter the progression of the clinical signs. However, the severity of this patient’s pneumonia at the time of the intravascular lymphoma diagnosis limited the aggressiveness of the chemotherapy. This patient may not have responded due to the progression at the time of diagnosis, limited application of the chemotherapy, individual variation, or the fact that the pathogenesis of this disease in dogs may differ from that in humans, as most human intravascular lymphomas are B-cell. Radiotherapy or plasmapheresis may have been useful, since these have been reported to be useful in human medicine.¹⁰¹⁶ The survival time of 6 months in this patient is similar to the short clinical course seen in most human patients.¹⁰

Conclusion

Intravascular lymphoma is a multisystemic disease in which neurological signs often dominate. Intravascular lymphoma should be suspected in middle-aged dogs with multifocal central or peripheral nervous system disease that have the following clinical signs: pulmonary thrombotic disease suggested by hypoxemia and increased alveolar-arterial gradients with unremarkable thoracic radiographs; dilated, tortuous retinal vessels; and thrombocytopenia. Central nervous system imaging followed by biopsy is a useful means of achieving the diagnosis. Increased vigilance for this disease, coupled with antemortem diagnostic techniques, should improve outcome, as chemotherapy in humans can occasionally achieve long-term disease-free survival or even complete remission.

Acknowledgments

The authors thank Mr. Ed Jensen for his assistance in designing the stereotaxic head holder; Dr. Sheldon Steinberg and Dr. Christina Barr for their assistance in preparing the manuscript; Dr. Linden Craig for the photomicrographs; and Herb and Michele Pitkowsky for their dedication to their dog, Star.