Ocular and multicentric lymphoma in a young racehorse


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Stephanie E. Germann
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A 6-year-old thoroughbred gelding was presented with a history of blepharospasm and opacity in the OS of 1 weeks’ duration. Ophthalmic examination findings were consistent with acute uveitis in the OS, and traditional treatment was initiated with systemic antibiotics and anti-inflammatory drugs, topical mydriatics, and corticosteroids. During the total treatment period of 4 weeks response to treatment was weak and the horse developed further problems such as cellulitis of the right hind limb with fever and eventually weight loss and dependent edema. Blood work was indicative of liver disease. Abdominal sonography revealed severe splenomegaly and slight hepatomegaly, and a liver biopsy confirmed malignant T-cell lymphoma. The horse was euthanized due to deteriorating general condition and subsequently underwent postmortem examination. Necropsy and histologic examination revealed a multicentric lymphoma with involvement of spleen, mesenteric lymph nodes, and OU.

The findings in this case demonstrate that the differential diagnosis of intraocular and systemic lymphoma should be considered in any horse presenting with anterior uveitis, especially when uveitis is unresponsive to treatment and when additional systemic signs of illness such as lethargy, fever, weight loss, or dependent edema arise.

Cytological examination of aqueous humor may provide a rapid diagnosis of intraocular lymphoma in eyes with clinical uveitis.


A 6-year-old thoroughbred gelding was presented to the Ophthalmology Section of the Equine Department, Vetsuisse Faculty, University of Zurich, Switzerland with the history of blepharospasm and opacity in the OS of 1 weeks’ duration. The horse was bright, alert, and in a good general condition. The ophthalmic examination in OS revealed positive menace response and dazzle reflex, while the pupillary light response (PLR) was negative. There was conjunctival hyperemia, the anterior chamber (AC) showed 3+ flare, as well as clotted blood and fibrin in the ventral aspect of the AC. The iris was swollen and the pupil was miotic (Fig. 1). Further examination of the posterior aspects of OS was not possible. The IOP was 18 mmHg in OS. The OD did not show any abnormality and had an IOP of 14 mmHg.

Figure 1.

OS at initial presentation: injected conjunctiva, swollen iris, miotic pupil, blood and fibrin settled in the ventral aspect of the anterior chamber.

An ultrasound examination was recommended for assessment of the posterior aspects of OS and prognostic evaluation, but was declined by the owner.

Ophthalmic examination findings were consistent with acute uveitis OS and therapy was initiated with intravenous flunixin meglumine (1 mg/kg q12 h; Fluniximin ad us. vet., Berna Veterinärprodukte AG, Bern, Switzerland) and gentamicin (7 mg/kg q24 h; Vetagent® ad us. vet., Veterinaria AG, Zurich, Switzerland), a single subconjunctival injection composed of 0.33 mg epinephrine, 3.3 mg atropine and 10 mg cocaine per mL (‘Sprengspritze nach Hollwich’, Sprengspritze KA, Kantonsapotheke Zurich, Zurich, Switzerland), and topical prednisolone eye drops (q8 h; Pred Forte® 1%, Allergan AG, Pfäffikon, Switzerland).

One day after initiation of treatment, the blood and fibrin clot in the AC had retracted and organized itself, while the pupil was still miotic. In order to prevent synechiation and to facilitate resolution of fibrin, an intracameral tissue plasminogen activator injection (20 µg tPA; Actilyse®, Boehringer Ingelheim, Ingelheim, Germany) as well as a second subconjunctival injection of combined atropine, epinephrine, and cocaine (‘Sprengspritze nach Hollwich’) was performed under general anesthesia. Aqueous humor, aspirated prior to tPA injection, was submitted for Leptospira antibody testing (microagglutination).

After recovery from general anesthesia, OS showed an intense hyphema. The next day the blood had settled to the ventral AC and the pupil was slightly dilated. The horse was released for further treatment with intravenous flunixin meglumine (1 mg/kg q12 h), topical prednisolone eye drops (q4 h), and atropine eye drops (q12 h; Atropin-POS® 1%, Ursapharm, Saarbrücken, Germany) at home.

A recheck 4 days later showed a slightly dilated pupil in OS, while the hemorrhagic uveitis was unchanged otherwise. Treatment with flunixin meglumine and topical prednisolone eye drops was continued at the same doses, while the topical atropine treatment was continued at a dosing interval of 24 h.

One week later, the gelding suddenly developed a cellulitis of the right hind limb with fever, and he was again presented at the Equine Department. OS still showed hemorrhagic uveitis. Blood work was performed and revealed leukocytosis (15 500/µL; normal range 4700–8200/µL), thrombocytopenia (51 000/µL; normal range 119 000–250 000/µL), monocytosis (2330/µL; normal range 0–184/µL), hyperbilirubinemia (86.5 µm; normal range 17.4–35.2 µm), a slight hypoproteinemia (51 g/L; normal range 60–70 g/L), as well as slightly increased liver enzyme activities (alkaline phosphatase (AP): 287 U/L; normal range 81–183 U/L, glutamate dehydrogenase (GLDH): 3.3 U/L; normal range 0.5–2.2 U/L, aspartate aminotransferase (AST): 526 U/L; normal range 229–393 U/L, sodium dehydrogenase (SDH): 12.6 U/L; normal range 0.1–7.6 U/L, lactate dehydrogenase (LDH): 7495 U/L; normal range 369–822 U/L). All other hematological and biochemical variables were within normal limits. Treatment consisted of walking the horse several times daily, hydrotherapy of the right hind limb, and administration of penicillin (30 000 IU/kg q12 h i.v.), gentamicin (7 mg/kg q24 h i.v.), flunixin meglumine (1 mg/kg q12 h i.v.), and prednisolone eye drops OS (q4 h).

Despite the intensive treatment protocol, both the cellulitis of the right hind limb as well as the uveitis of OS only showed partial and minimal response to therapy.

Three weeks after initial presentation, a slight improvement of the uveitis OS was noted. OS showed positive menace and dazzle reflexes, PLR was negative due to atropine treatment. The conjunctivae were still injected, the ventral hemorrhage in the AC had formed a solid blood clot, the flare was reduced to 1+, the iris still appeared thickened, and the pupil was slightly dilated. The reduced intraocular inflammation allowed direct ophthalmoscopy for fundus examination for the first time and showed no abnormalities.

Four weeks after initial presentation the horse suddenly developed a decrease in general condition such as weight loss with unchanged appetite and dependent edema. Blood analysis was repeated and showed leukocytosis (9500/µL), thrombocytopenia (40 000/µL), hyperbilirubinemia (93.3 µm), even further increased liver enzyme activities (AP: 379 U/L, GLDH: 5.8 U/L, AST: 918 U/L, GGT: 34 U/L SDH: 27.9 U/L, LDH: 18 389 U/L), increased bile acid concentrations (24.9 µm; normal range 0–20 µm), and hyperlipemia (triglycerides: 11.8 mm; normal range 0.1–0.5 mm). PCR for Anaplasma phagocytophilum, as well as serologic testing for Theileria equi and Babesia caballi was negative, as was the result of antibody testing for leptospirosis in aqueous humor and serum.

An ultrasound examination of the abdomen revealed splenomegaly, slight hepatomegaly, and mild abdominal effusion. Liver biopsies were taken and submitted for cytologic and histologic evaluation. Cytology smears showed groups of hepatocytes with a moderate amount of bile pigment granula in the cytoplasm, a moderate number of lymphocytic cells, predominantly lymphoblasts, with an intensive basophilic, small size vacuolized cytoplasm and round to ovoid to indented nuclei with a coarsely stippled chromatin structure, along with a moderate number of macrophages. Based on these findings, a malignant lymphoma was suspected. Histologic evaluation showed few solitary cells with large round nuclei with loose chromatin structure in the sinusoids, immunohistochemistry was positive for CD3 (CD79a negative) and confirmed a malignant T-cell lymphoma. Shortly after, the horse was euthanized due to deterioration of its clinical condition, and the body was sent in for postmortem examination.

Gross pathologic findings included a markedly enlarged spleen with rounded edges and general enlargement of the abdominal lymph nodes. The liver was macroscopically inconspicuous. H&E stained sections of spleen and lymph nodes revealed a homogenous periarteriolar population of large, mononuclear, round neoplastic cells with eosinophilic cytoplasm, large, round to ovoid, sometimes gyriform nuclei with loose chromatin structure and 1–2 nucleoli, predominantly in the white pulp (Fig. 2). Immunohistochemically, tumor cells were positive for CD3 (specific for T-lymphocytes) and negative for CD79a (specific for B-lymphocytes), leading to the diagnosis of a T-cell lymphoma (Fig. 3a,b). In addition, a low number of intravascular and intrasinusoidal neoplastic lymphocytes were homogenously distributed in liver, lung, and kidneys. Sections of OU revealed multifocal infiltrates of neoplastic lymphocytes (Fig. 4). In OS, dense tumor cell infiltration was seen in the choroid, dorsally and ventrally, the ciliary body, and the severely thickened iris (Fig. 5a,b). The limbus was only mildly affected, and no other structures were involved. In OD, the choroid was only affected ventrally, the limbus, and ciliary body were mildly infiltrated; however, additional neoplastic infiltrates were seen in the optic nerve and the periocular fat tissue (Fig. 6a–d). Aqueous humor was taken during necropsy and examined cytologically. A moderately increased cell number with the dominance of large neoplastic lymphoblasts with dark basophilic cytoplasm and large, round nuclei containing irregular chromatin, and several nucleoli was observed in OS (Fig. 7). Aqueous humor of OD and cytologic smears of vitreous from OU were inconspicuous. H&E stained sections of the right hind limb revealed a severe suppurative cellulitis, but no neoplastic infiltrates.

Figure 2.

T-cell lymphoma in the spleen showing multiple neoplastic lymphocytes (arrows) with eosinophilic cytoplasm, large round to ovoid, sometimes gyriform nuclei with loose chromatin structure and 1–2 small nucleoli. H&E, ×40.

Figure 3.

Immunohistochemical labeling of T-cell lymphoma in the spleen (a) neoplastic lymphocytes staining positive for CD3 (specific for T-lymphocytes) and (b) negative for CD79a (specific for B-lymphocytes). CD3 and CD79a immunohistochemical stains, ×40.

Figure 4.

Histological section of OS. Note the markedly thickened iris due to massive tumor cell infiltration and the blood and fibrin exudate in the anterior chamber. H&E.

Figure 5.

Histological sections of iris (a) and choroid (b) OS showing multifocal infiltration with neoplastic lymphocytes (arrows). H&E, ×40.

Figure 6.

Histological sections of the limbus (a), choroid (b), optic nerve (c), and periocular fat (d) OD showing tumor cell infiltrates at multiple sites (arrows). H&E, ×20.

Figure 7.

Aqueous humor cytology of OS showing neoplastic lymphoblasts with dark blue cytoplasm and large, round nuclei containing irregular chromatin and several nucleoli. Wright, ×100.


Initial clinical findings such as blepharospasm, aqueous flare, hemorrhage, and fibrin in the AC, as well as the miotic pupil in our patient were consistent with acute uveitis OS. Differential diagnoses for uveitis in the horse include blunt and penetrating trauma with direct trauma to the lens capsule, systemic infectious diseases caused by viruses (EHV-1, equine Influenza), and bacteria (Salmonella, Streptococcus equi var. equi, Borrelia burgdorferi, Rhodococcus equi), septicemia in neonatal foals, neoplasia, and immune mediated uveitis such as equine recurrent uveitis (ERU).1

Immune mediated uveitis was considered the most likely diagnosis according to the predominant portion of ERU cases among our patients. Differential diagnoses such as traumatic uveitis could be excluded based upon lack of trauma history and visible external injury, respectively, phacoclastic uveitis was ruled out based on ophthalmic examination findings, such as intact cornea and sclera, and infectious uveitis seemed less probable because of the normal general condition of the patient. Neoplasia may or may not have been ruled out with an ultrasound examination of the eye. Since this was declined by the owner of the horse and neoplasia was not at the top of our list of differential diagnoses, ocular sonography was not performed.

The treatment that was instituted is the standard uveitis therapy in our clinic. It consists of systemic nonsteroidal anti-inflammatory drugs, combined with antibiotics in severe cases, topical steroids, and atropine. Whenever there is marked miosis, a subconjunctival injection of a combination of epinephrine, atropine, and cocaine (i.e. ‘Sprengspritze nach Hollwich’) is performed. This combination is a very potent mydriatic and cycloplegic that is applied in case of significant ciliary spasm.2

The refractory, therapy-resistant uveitis, the deteriorating general condition, and the splenomegaly and hepatomegaly found in our patient were suggestive of neoplastic disease. Increased liver enzyme activities and bile acid concentrations were indicative for hepatic involvement, and liver biopsy finally provided the diagnosis of T-cell lymphoma.

Equine lymphoma is rarely encountered in the ocular region; other organs involved more frequently include lymph nodes, intestines, other viscera, skin, and upper respiratory tract.3 Ocular lymphoma concerns mainly the adnexa, but may also cause uveitis, corneoscleral masses, or retrobulbar infiltration.4–7 Even though lymphoma is the most common tumor of the hemolymphatic system in horses,8 its prevalence in the equine population is relatively low (0.002–0.05% and 0.2–3.0%, depending on the study), especially when compared with other domestic animals, such as cows, dogs, and cats.3,9 This low prevalence of equine lymphoma represents a certain risk to exclude this disease from clinical differential diagnosis in horses until the disease becomes chronic and unresponsive to conventional treatments,7 even more so if the horse is in normal general condition as in this case at initial presentation.

The pathogenesis of systemic equine lymphoma remains obscure. There are currently no known risk factors. Most affected horses are young adults between 4 and 10 years of age. No breed or sex predisposition has been demonstrated.3 Four anatomic forms of lymphoma are described: multicentric, alimentary, mediastinal, and extranodal. Multicentric or generalized lymphoma is the most commonly reported form and involves multiple peripheral and internal lymph nodes and other organs. Multicentric lymphoma was diagnosed in the present case. The multiple sites of involvement most probably represent metastasis via blood and lymphatic circulatory systems. Notably, this is the most common form of lymphoma to be associated with circulating neoplastic lymphocytes, referred to as ‘leukemic phase’ of lymphoma.3 Because intraocular structures have no lymphatic channels, metastatic tumors reach the uvea solely by the hematogenous (arterial) route.10 In dogs the uvea seems to be a predilection site for hematogenously metastasizing tumors like lymphoma.11 Most animals are bilaterally affected with uveitis being the most common presentation.12,13 In a retrospective study of 21 horses with ocular lymphoma, only four animals showed uveitis; three horses presented with bilateral, one horse with unilateral uveitis.5

Clinical signs of lymphoma reflect dysfunction of affected organs and the course of the disease is typically rapid once signs become evident, as seen in our patient.3 Intraocular lymphoma cannot usually be differentiated from other potential causes of anterior uveitis on the basis of ocular signs alone.9 Because of the diversity of nonspecific signs diagnosis of lymphoma can be difficult and ante mortem confirmation occurs in < 60% of cases.3 Definitive diagnosis of lymphoma requires the observation of neoplastic cells in aspirates or biopsy specimens.3

In the presented horse, ante mortem diagnosis was made by histologic identification of neoplastic lymphocytes in the liver sinusoids and confirmed by use of immunohistochemistry. Postmortem evaluation revealed that multiple organs including spleen, mesenteric lymph nodes, and OU were involved. Postmortem aqueous humor cytology revealed neoplastic lymphocytes only in OS and not in OD. As OU were affected histologically, but only OS showed uveitis clinically, we assume that the neoplastic infiltration must be advanced in order to cause a breakdown of the blood–aqueous barrier and release of tumor cells into the aqueous humor. This hypothesis is supported by the fact that aqueous humor cytology was only diagnostic in the eye with clinical uveitis.


Ocular signs can represent first clinical signs of multicentric lymphoma in horses.5 Intraocular neoplasia such as lymphoma should therefore be included as a differential diagnosis in horses with refractory uveitis unresponsive to traditional treatment, especially when additional systemic signs arise. Cytologic examination of aqueous humor may provide a rapid diagnosis of intraocular lymphoma in eyes with clinical uveitis.


The authors thank Dr Beat Hauser and Dr Franco Guscetti for their help with documentation and interpretation of the cytological and histological preparations.