Abstract. Clinical, laboratory and tissue findings from 37 horses with lymphoma were investigated. Horses ranged in age from 0.3 to 20.5 years (median 5.0 years) and included 18 females and 19 males. Weight loss (n 5 25) and ventral edema (n 5 21) were the most common historical and physical abnormalities. The most common laboratory abnormalities were hyperfibrinogenemia (n 5 26), hypoalbuminemia (n 5 19), anemia (n 5 19), leukemia (n 5 14), hyperglobulinemia (n 5 13), and thrombocytopenia (n 5 13). Thirty-four tumors involved multiple lymphoid tissues and abdominal or thoracic organs, and 3 tumors were restricted to cutaneous and subcutaneous sites. Histopathologically, all tumors diffusely effaced normal lymph node architecture. Tumor cell morphology was heterogeneous in 17 tumors, and 8 tumors had marked histiocytic and multinucleated giant cell infiltrates. Extensive necrosis or focal fibrosis was present in 22 and 4 lymphomas, respectively. Staining of tumor sections with antibodies against CD3 and CD79a molecules resulted in classification of T-cell (n 5 26) or B-cell (n 5 7) origin. Four tumors could not be classified. Most T-cell tumors comprised small to medium CD3 + lymphocytes, whereas 5 of 7 B-cell tumors were infiltrated by numerous small T lymphocytes and classified as T-cell-rich B-cell lymphoma. Neither estrogen nor progesterone receptor expression was consistently identified by immunochemical assessment of tumor tissues. Fresh tumor cells from 6 horses bound antibodies reactive with equine CD4, CD5, CD8, CD21, or major histocompatibility class II molecules, confirming T-cell (n 5 5) or B-cell origin (n 5 1). These findings suggest that T-cell lymphoma is more common than B-cell lymphoma in horses and that inflammation, possibly from tumor cytokine production, is frequent.

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Pancytopenia was observed in two 3-year-old geldings and one 11-year-old mare. All horses had a brief history (2 days to 4 weeks) of fever, anorexia, and depression. One of the three horses had blast cells present on a peripheral blood smear. Examination of the bone marrow showed substantial infiltration with neoplastic lymphoid cells. At necropsy, neoplastic cells were restricted to the bone marrow in one horse, present in bone marrow, liver, and spleen in the second horse, and reported in multiple tissues in the third horse, including bone marrow, kidneys, lung, myocardium and lymph nodes. The value of a bone marrow aspirate and core biopsy in the investigation of pancytopenia is highlighted. LYMPHOMA, or lymphosarcoma, seems to be uncommon in the horse, especially when the prevalence of the neoplasm is compared with that of the dog, cat, and cow. ' Retrospective surveys of equine neoplasia diagnosed from necropsy or biopsy have placed the prevalence of equine lymphoma at between 0.4% and 4.8% of tumors of the h~r s e .~.~ Clinically, the disease in the horse has been separated into mediastinal, alimentary, multicentric, cutaneous, and leukemic forms. Combinations of two or more ofthese forms have been rep~rted.~.' Lymphoid leukemia, by definition, describes a neoplastic proliferation of lymphoid cells within the bone marrow and/ or peripheral blood. It may occur as a primary leukemia, in which the bone marrow is the primary site of involvement, or as an advanced stage of lymphoma, in which the bone marrow may become infiltrated with neoplastic lymphocytes from peripheral tissues.6.8 Primary lymphoid leukemia seems to be particularly rare in the horse, with very few cases reported in the literat~re.'.','~ This article describes three horses that were referred to the Veterinary Medical Teaching Hospital (VMTH) at the University of Florida over a 4-month period in 199 1. The horses had histories of fever, anorexia, and depression. Pancytopenia was evident in each of the horses on initial laboratory assessment. Subsequent investigation confirmed the diagnosis of lymphoproliferative disease with bone marrow myelophthisis. Horse 1A 3-year-old Quarter Horse gelding was seen at the VMTH because of a 4-week history of intermittent anorexia, weight loss, and fever. The gelding had been treated for mild colic at the time that the clinical signs were first identified. The vaccination and deworming history was considered adequate for the region, and a negative Coggin's test had been obtained 5 months before referral.On presentation, the gelding was in poor body condition and had a rough hair coat. The animal was depressed. Rectal temperature was increased (39.1 "C), as was the resting pulse rate (64 beats/min) and respiratory rate (36 breaths/min). Petechial hemorrhages were present in the nasal and oral mucosa, and a grade 2/6 systolic murmur was ausculted over the left heart base.There was pancytopenia, including a nonregenerative anemia (packed cell volume (PCV) l l % , hemoglobin (Hb) 4.2g/dL, red blood cell (RBC) cou...

Background: Accuracy of baseline ACTH for the diagnosis of PPID in horses varies between studies.Objectives: To estimate the diagnostic accuracy of ACTH as a biomarker for PPID in adult horses and appraise potential causes of heterogeneity. Study design: Systematic review and meta-analysis.Methods: A literature review identified studies reporting diagnostic accuracy data for extraction. Risk of bias was evaluated using QUADAS-2. Two random-effects models, the hierarchical summary receiver operating curve (HSROC) and the bivariate binomial normal model (BBN) were used to pool accuracy measurements. We performed meta-regression using study-level variables. The impact of diagnostic test accuracy on the frequency of false-positive and false-negative results at various pretest probabilities was calculated using the BBN model's accuracy results. Results:Patient selection and index test evaluation demonstrated significant risk of bias. Mean and 95% confidence intervals for sensitivity and specificity for all studies (n = 11) based upon the HSROC model were (0.72, 95% CI: 0.62 to 0.82) and (0.88, 95% CI: 0.79 to 0.93), respectively. When studies with a common positivity threshold of 35 pg/mL ACTH were evaluated (n = 6), sensitivity and specificity were (0.66, 95% CI:0.54 to 0.77) and (0.87, 95% CI: 0.74 to 0.94). In a hypothetical group of one thousand horses with PPID prevalence of 2%, 20%, and 90%, the frequency of resulting false-positive and false-negatives would be (127 and 7), (104 and 68) and (13 and 306), respectively. Factors leading to increased accuracy were case-control design, clinical reference standard and data-driven choice of ACTH threshold.Main limitations: A small number of primary studies (n = 11) were available, demonstrating significant biases. Conclusions:Less biased studies examining diagnostic accuracy of ACTH are needed.In horses with a high pretest probability of PPID, ACTH may be a functional "rule-in" test. Baseline ACTH is not recommended for screening purposes or use in horses without clinical signs of PPID.

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