History
A 10-year-old 24.6-kg (54.1-lb) spayed female German Shepherd Dog mix was evaluated because of signs of cervical pain of 1 month's duration and acute left pelvic limb lameness of 5 days’ duration.
Clinical and Clinicopathologic Findings
Physical examination revealed signs of pain during left tarsal joint manipulation and an enlarged left popliteal lymph node. Mild to moderate effusion was evident in the left tarsal region (Figure 1). Neurologic examination findings were considered normal other than signs of pain that were elicited on palpation of the midcervical region. Radiography revealed no obvious cervical abnormalities; however, mild thickening of the soft tissues along the lateral aspect of the left tarsal joint and generalized reduction in the radiopacity of the left talus were evident. A CBC revealed no remarkable findings; no cellular atypia was noted. Results of a serum biochemical panel included mildly high alanine aminotransferase activity (84 U/L; reference interval, 3 to 69 U/L) and minimally to mildly high alkaline phosphatase activity (161 U/L; reference interval, 20 to 157 U/L); the concentrations of globulins and total protein were 3.9 g/dL (reference interval, 1.7 to 3.8 g/dL) and 7.3 g/dL (reference interval, 4.8 to 6.9 g/dL), respectively. On T2- and T1-weighted MRI images of the cervical portion of the vertebral column, there was an 11.7 × 4.3 × 4.5-cm, mixed hyper- and hypointense, central-contrast-enhancing, lobulated mass in the right ventral cervical region. The mass displaced the trachea and esophagus to the left and ventrally and was located within the region of the right medial retropharyngeal lymph node and the cranial aspect of the right mandibular salivary gland. Thoracic radiographic findings were apparently normal; there was no obvious evidence of lymph node enlargement. Abdominal imaging was declined by the owner.
Photograph of the craniodistal aspect of the left pelvic limb (proximal to distal view) of a 10-year-old dog that was evaluated because of signs of cervical pain of 1 month's duration and acute left pelvic limb lameness of 5 days’ duration. Signs of pain were elicited on manipulation of the tarsal joint and mild to moderate tarsal joint effusion was palpable.
Citation: Journal of the American Veterinary Medical Association 255, 2; 10.2460/javma.255.2.177
Photograph of the craniodistal aspect of the left pelvic limb (proximal to distal view) of a 10-year-old dog that was evaluated because of signs of cervical pain of 1 month's duration and acute left pelvic limb lameness of 5 days’ duration. Signs of pain were elicited on manipulation of the tarsal joint and mild to moderate tarsal joint effusion was palpable.
Citation: Journal of the American Veterinary Medical Association 255, 2; 10.2460/javma.255.2.177
Photograph of the craniodistal aspect of the left pelvic limb (proximal to distal view) of a 10-year-old dog that was evaluated because of signs of cervical pain of 1 month's duration and acute left pelvic limb lameness of 5 days’ duration. Signs of pain were elicited on manipulation of the tarsal joint and mild to moderate tarsal joint effusion was palpable.
Citation: Journal of the American Veterinary Medical Association 255, 2; 10.2460/javma.255.2.177
Formulate differential diagnoses from the history, clinical findings, and Figure 1—then turn the page→
Cytologic Findings
Following radiography and MRI, fine-needle aspirate specimens of the cervical mass and the left prescapular and popliteal lymph nodes and a left tarsal synovial fluid sample were collected for microscopic examination. Biopsy of the left popliteal lymph node was performed under anesthesia.
The cytologic features of the cervical mass and prescapular lymph node specimens were highly similar (Figure 2). The specimens were of moderate to high cellularity and contained intermediate to large lymphocytes. In both specimens, cells were round to oval (maximum dimension, 20 to 25 μm) with moderately abundant basophilic cytoplasm containing numerous small, punctate, colorless vacuoles. Nuclei were round to oval to indented (maximum dimension, 15 to 22 μm) with fine, evenly distributed chromatin. The nuclei contained 1 to 3 prominent, irregularly shaped, blue nucleoli. These cells had occasional mitotic figures and high nuclear-to-cytoplasmic ratios. Rare foamy macrophages, often with evidence of leukophagia, were present.
The aspirate specimen of the popliteal lymph node was of moderate to high cellularity (Figure 2). The nucleated cells composed a primarily monomorphic round cell population; scattered activated macrophages were also present. The round cell population consisted of cells that had mild anisocytosis (20 to 25 μm) with scant amounts of deeply basophilic cytoplasm. The cells’ cytoplasm often contained discrete, colorless vacuoles. The nuclei of these cells were round (15 to 22 μm in diameter) and contained fine to coarse chromatin in addition to 1 to 3 prominent nucleoli. Bizarre mitotic figures were observed throughout.
The preparation of synovial fluid obtained from the left tarsal joint contained few intact cells and was of moderate to high cellularity (Figure 2). The cells were a monomorphic population of intermediate to large lymphocytes that closely resembled the cells in the specimens of the lymph nodes and the cervical mass. Rare foamy macrophages were seen within the sample; these macrophages, at times, had evidence of leukophagia. Rare osteoclasts were also present within the sample. The cytologic findings for all specimens were interpreted as malignant neoplasia, probably lymphoma. Because of the location of the cervical mass, this mass was likely a mandibular lymph node.
Photomicrographs of fine-needle aspirate specimens obtained from a mass in the right ventral cervical region (A), the left prescapular lymph node (B), and the left popliteal lymph node (C) and a sample of synovial fluid (D) obtained from the left tarsal joint of the dog in Figure 1. The specimens from the mass and the prescapular lymph node (A and B) have a similar population of round cells wherein mild anisocytosis (cell diameters, 20 to 25 μm) is observed. The cells have basophilic cytoplasm in which discrete, colorless vacuoles are present. An activated macrophage is present in the specimen from the prescapular lymph node (B). In the popliteal lymph node specimen (C), a monomorphic population of round cells is present. The tarsal joint synovial fluid specimen (D) contains a monomorphic population of intermediate to large lymphocytes. The lymphocytes’ nuclei have 1 to 3 prominent, irregularly shaped, blue nucleoli. Modified Wright stain; bar in panels A and B = 10 μm, and bar in panels C and D =15 μm.
Citation: Journal of the American Veterinary Medical Association 255, 2; 10.2460/javma.255.2.177
Photomicrographs of fine-needle aspirate specimens obtained from a mass in the right ventral cervical region (A), the left prescapular lymph node (B), and the left popliteal lymph node (C) and a sample of synovial fluid (D) obtained from the left tarsal joint of the dog in Figure 1. The specimens from the mass and the prescapular lymph node (A and B) have a similar population of round cells wherein mild anisocytosis (cell diameters, 20 to 25 μm) is observed. The cells have basophilic cytoplasm in which discrete, colorless vacuoles are present. An activated macrophage is present in the specimen from the prescapular lymph node (B). In the popliteal lymph node specimen (C), a monomorphic population of round cells is present. The tarsal joint synovial fluid specimen (D) contains a monomorphic population of intermediate to large lymphocytes. The lymphocytes’ nuclei have 1 to 3 prominent, irregularly shaped, blue nucleoli. Modified Wright stain; bar in panels A and B = 10 μm, and bar in panels C and D =15 μm.
Citation: Journal of the American Veterinary Medical Association 255, 2; 10.2460/javma.255.2.177
Photomicrographs of fine-needle aspirate specimens obtained from a mass in the right ventral cervical region (A), the left prescapular lymph node (B), and the left popliteal lymph node (C) and a sample of synovial fluid (D) obtained from the left tarsal joint of the dog in Figure 1. The specimens from the mass and the prescapular lymph node (A and B) have a similar population of round cells wherein mild anisocytosis (cell diameters, 20 to 25 μm) is observed. The cells have basophilic cytoplasm in which discrete, colorless vacuoles are present. An activated macrophage is present in the specimen from the prescapular lymph node (B). In the popliteal lymph node specimen (C), a monomorphic population of round cells is present. The tarsal joint synovial fluid specimen (D) contains a monomorphic population of intermediate to large lymphocytes. The lymphocytes’ nuclei have 1 to 3 prominent, irregularly shaped, blue nucleoli. Modified Wright stain; bar in panels A and B = 10 μm, and bar in panels C and D =15 μm.
Citation: Journal of the American Veterinary Medical Association 255, 2; 10.2460/javma.255.2.177
Histopathologic Findings
On histologic examination, there was diffuse effacement of the normal popliteal nodal architecture by a neoplastic proliferation of large lymphocytes, each of which had a smooth nuclear membrane, dispersed to vesicular chromatin, and a prominent and single central nucleolus. There were 29 mitotic figures/4 hpf (200×). Less than 10% of the lymphocytes were small in size (resident lymphocytes). Numerous tingible body macrophages were present. Immuno-histochemical analysis revealed the neoplastic cells to be negative for CD3 and Pax5 (the Pax5 gene encodes the B-cell–specific activator protein). There was mild-to-moderate nonspecific nuclear and cytoplasmic labeling for CD79a. The cell origin of the lymphoma could not be confirmed by immuno-histochemical analysis; a PCR assay for antigen receptor rearrangements (PARR) performed on popliteal node tissue was declined by the owner.
Morphologic Diagnosis and Case Summary
Morphologic diagnosis and case summary: multicentric lymphoma associated with involvement of a synovial joint in a dog.
Comments
The owner continued to decline further diagnostic workup (eg, abdominal imaging and bone marrow biopsy) for the dog of the present report. However, chemotherapy was pursued, and the dog was started on a vincristine, cyclophosphamide, doxorubicin, and prednisone (CHOP) protocol. A CBC was performed once while the dog was undergoing chemotherapy (8 days after commencement of the CHOP protocol), and the presence of circulating atypical cells was not noted. The CBC did reveal lymphopenia; the WBC count at that time was 5,000 cells/μL (reference interval, 6,000 to 17,000 cells/μL) and the platelet count was 183,000 platelets/μL (reference interval, 200,000 to 900,000 platelets/μL). No other hematologic changes were identified. For management of cervical and joint pain, the dog was administered both tramadol and gabapentin. On repeated examination 8 days following initiation of chemotherapy, the left tarsal joint effusion was more pronounced, and the left popliteal lymph node had increased in size by an estimated 18%. The chemotherapy protocol was changed; a protocol involving l-asparaginase, lomustine, and prednisone was initiated. Five days following the second round of chemotherapy, the dog's lameness had progressed, and the popliteal lymph node size had increased by an estimated 60%. The owner elected euthanasia of the dog, and a necropsy was declined.
Malignant lymphoma is considered to be the most common canine tumor regularly treated with chemotherapy in veterinary medicine.1,2 It is a cancer common among dogs of any age and any breed.1,2 Among affected dogs, often the first observed physical examination finding is marked enlargement of 1 or more peripheral lymph nodes. Diagnosis of lymphoma is made on the basis of results of either cytologic or histologic examination of lymph node specimens. Immunophenotyping is commonly performed to determine whether neoplastic lymphoma cells are of B- or T-cell origin. B-cell lymphoma cells are negative for CD3, yet positive for CD79a and Pax5. The CD3 antigen is bound to the mature T-cell membrane, whereas the CD79a antigen is found on the B-cell membrane. Pax5 is considered a nuclear transcription factor protein3; it is involved in organ development and tissue differentiation. Staining for Pax5 yields positive results for B-cell lymphomas and, to date, negative results for T-cell lymphomas.4,5 In the case described in the present report, immunophenotyping was performed on a sample of the dog's left popliteal lymph node. The lymphocytes were negative for CD3 and Pax5; there was nonspecific nuclear and cytoplasmic labeling for CD79a. Thus, the cells were not specifically of B- or T-cell lineage, suggesting that the diagnosis was that of null-cell lymphoma. Null-cell lymphoma is a rare form of lymphoma; a recent study by Ponce et al4 revealed that among 608 cases of canine malignant lymphoma, only 5 (0.8%) involved the null-cell variant. Among those 5 affected dogs, the median age was 8.4 years; most were female (4 dogs) and all had generalized lymphadenopathy at the time of diagnosis. Interestingly, however, none of the 5 dogs had extranodal involvement, as was evident in the dog of the present report.
In addition to immunophenotyping, the biological behavior of lymphoma is also very important when it comes to classifying the cancer and prognostication. Currently, the World Health Organization (WHO) system of classification of canine lymphomas is considered the best classification system in veterinary oncology.1 Results of a study by Valli et al1 confirmed that veterinary pathologists, even those who do not specialize in hematopathology, achieved high accuracy in classification of a variety of canine lymphoma samples when using the WHO system. Factors considered in the WHO system for classification of lymphomas include growth pattern (nodular vs diffuse), relation of cellular nodules to remnants of nonneoplastic follicles, nuclear size, nuclear morphology, mitotic rate, and neoplastic cell immunophenotype. The most common lymphoma subtype is diffuse large B-cell lymphoma.1 With more regular use of a standardized classification system, such as the WHO system, more accurate information can be gathered regarding the biological activity of lymphoma subtypes, and diagnostic testing and treatment methods can likely be improved.
Synovial lymphoma, a rare anatomic classification in both domestic animals and humans, is not easily classified according to the WHO system guidelines. In humans, most synovial lymphomas are of T-cell origin.6 In the veterinary medical literature, there are only 2 previously published case reports7,8 that describe involvement of synovium by lymphoma. In 1 report,7 a dog developed left pelvic limb lameness; examination of a synovial biopsy specimen from the left stifle joint revealed T-cell lymphoma. Peripheral lymph node enlargement was not noted at the time of diagnosis in that case report. The dog was later euthanized, and necropsy revealed lymphoma within the urinary bladder, urethra, spleen, lungs, skin, kidneys, and the musculature surrounding the left stifle joint. However, on the basis of the results of cytologic examination of samples obtained from various sites and by arthrocentesis as well as the histopathologic findings for tissue from the popliteal lymph node, a diagnosis of multicentric lymphoma with unknown lineage and synovial involvement was made. The final diagnosis in that reported case was synovial lymphoma with multicentric involvement.7
In the other case report8 of involvement of the synovium by lymphoma, a sheep developed bilateral pelvic limb lameness. At necropsy, synovial lymphoma of both tarsal joints was diagnosed. Compared with the case report involving the dog,7 there were no gross or histopathologic findings of lymphoma elsewhere in the sheep cadaver at the time of necropsy. The final diagnosis in that sheep was synovial lymphoma without multicentric involvement.
In the case described in the present report, biopsy of the left tarsal joint synovial membrane and necropsy of the dog were declined by the owner. However, given the cytologic findings for the cervical mass, tarsal synovial fluid sample, and the left prescapular lymph node in addition to the cytologic and histopathologic findings for the left popliteal lymph node, a diagnosis of multicentric lymphoma with synovial involvement was made for this dog.
Acknowledgments
The authors thank Dr. Craig A. Thompson for photomicrography of the cytology preparations.
References
1. Valli VE, San Myint M, Barthel A, et al. Classification of canine malignant lymphomas according to the World Health Organization criteria. Vet Pathol 2011;48:198–211.
2. Valli VE, Kass PH, San Myint M, et al. Canine lymphomas: association of classification type, disease stage, tumor subtype, mitotic rate, and treatment with survival. Vet Pathol 2013;50:738–748.
3. Feldman AL, Dogan A. Diagnostic uses of Pax5 immunohistochemistry. Adv Anat Pathol 2007;14:323–334.
4. Ponce F, Marchal T, Magnol JP, et al. A morphologic study of 608 cases of canine malignant lymphoma in France with a focus on comparative similarities between canine and human lymphoma morphology. Vet Pathol 2010;47:414–433.
5. Willmann M, Müllauer L, Guija de Arespacochaga A, et al. Pax5 immunostaining in paraffin-embedded sections of canine non-Hodgkin lymphoma: a novel canine pan pre-B- and B-cell marker. Vet Immunol Immunopathol 2009;128:359–365.
6. Mariette X, de Roquancourt A, d'Agay MF, et al. Monarthritis revealing non-Hodgkin's T-cell lymphoma of the synovium. Arthritis Rheum 1988;31:571–572.
7. Lahmers SM, Mealey KL, Martinez SA, et al. Synovial T-cell lymphoma of the stifle in a dog. J Am Anim Hosp Assoc 2002;38:165–168.
8. Pearson GR, Day MJ, Main D, et al. B-cell (CD79a) lymphoma affecting the tarsal joint synovia in a sheep. J Comp Pathol 1999;120:295–299.
