Gross lesions, microscopic appearance, and immunophenotyping are reported in a retrospective study of 31 cases of equine malignant lymphoma. Immunohistochemical studies were performed on archived formalin-fixed, paraffin-embedded tissues. Monoclonal antibodies to surface glycoprotein BLA.36 and intracytoplasmic domains of mb-1 and B29 were used to document the presence of B lymphocytes in the equine tumors. Polyclonal antibody to CD3 and monoclonal antibodies to T-lymphocyte markers CD3 and CD5 revealed the presence of variable numbers of T cells within the equine lymphomas. The neoplastic component of the equine lymphomas was determined through morphologic evaluation, immunophenotyping, and the use of proliferation markers Ki-67 and proliferating cell nuclear antigen. Equine malignant lymphomas were composed of a heterogeneous cell population. Most tumors contained B and T lymphocytes. Twenty-four horses had diffuse lymphomas derived from B lymphocytes. Thirteen of these lymphomas contained primarily neoplastic B lymphocytes. Eleven additional cases of diffuse large B-cell lymphoma contained from 40% to 80% nonneoplastic T lymphocytes and were classified as T-cell-rich, large B-cell lymphomas. This is the first description of T-cell-rich, B-cell lymphoma in the horse. Six tumors with a diffuse architecture were derived from T lymphocytes. Four T-cell tumors were large-cell tumors, 1 was a small-cell tumor, and in 1 tumor the size of the cells could not be determined accurately because of autolytic change in the tissues. One diffuse large-cell lymphoma did not react with either B- or T-cell markers.

Neuromuscular signs in association with hypothyroidism are described in 29 dogs. Eleven dogs had lower motor neuron signs, 9 had peripheral vestibular deficits, 4 had megaesophagus, and 5 had laryngeal paralysis. Primarily older (mean = 9.5 years), large-breed dogs were affected, and there was no sex or breed predisposition. Duration of clinical signs before presentation ranged from 2 to 8 weeks (mean = 5 weeks). The diagnosis was based on (1) results of neurological examination (29 dogs); (2) electromyographic abnormalities (1 8 dogs), including fibrillation potentials (n = 18). positive sharp waves (n = 15). and complex repetitive discharges (n = 4); (3) high serum cholesterol concentration (1 0 dogs: mean = 335 mg/dL); (4) low response to thyroid-stimulating hormone (29 dogs; mean T4 prestimulation concentration = 0.8 ag/dL; mean T4 poststimulation = 1.2 pg/dL); and (5) good response to thyroxine supplementation (26 dogs). Dogs with vestibular deficits had abnormal brainstem auditory-evoked responses (BAER), including increased latencies of P, -P6 and decreased amplitude of P4,5-N5. Seven other dogs had similar BAER abnormalities without manifesting clinical rimary hypothyroidism'-' is a relatively common endo-

Abstract. Cytologic and histologic examination of 91 canine mammary masses was performed by two cytologists and two histopathologists. Ten important cytologic criteria of malignancy for canine mammary tumors were identified. A cytologic grading system for differentiation of benign from malignant mammary tumors was proposed using these criteria. With this system, approximately one fourth of the malignant mammary tumors were given a concordant cytologic diagnosis. Approximately one-half of the benign masses were given a concordant cytologic diagnosis by the two cytologists. One-half of all the tumors examined were given inconclusive cytologic diagnoses by both cytologists. The cytologic identification of spindle cells did not differentiate complex and mixed mammary tumors from simple tumors. Only five of the animals studied died of mammary cancer, precluding a critical analysis of the cytologic criteria for prediction of cancer mortality.Tumors of the mammary gland are a common clinical problem in the adult bitch, comprising up to 52% of all neoplasm^.^ The frequency of malignancy among mammary tumors is approximately 50%.4~8~28 The disease is commonly multicentric, and tumors in a single dog may be of more than one type.9,25,32.36 Clinical findings identified by history or physical examination that could indicate malignancy include a tumor diameter of greater than 5 cm, recent rapid growth, infiltration of surrounding tissues, erythema, and edema.3,4,34 Most canine mammary tumors (Le., benign and malignant) exhibit none of these findings. Other prognostic indicators (i.e., cellular differentiation and invasion of surrounding stroma) are identifiable only through histologic examination. Since the most common treatment for canine mammary neoplasia is surgical excision, definitive therapy often is pursued prior to diagnosis of the disease.The safety of fine needle aspiration cytology as a preoperative diagnostic test of breast cancer in women has been e s t a b l i~h e d .~,~~ It has been shown to be highly accurate (false positive rate less than 1%) in studies comparing cytologic with subsequent histologic findings.11,20,43,44 In a comparable study in the dog, 19 mammary tumors were examined cytologically and histologically. Eight out of 17 mammary carcinomas were given a concordant cytologic diagnosis, and two adenomas were diagnosed cytologically as carcinoma. l5

Ponies given dried red maple (Acer rubrum L.) leaves at a dose of 3.0 gm/kg body weight became ill and died one to five days after administration of the leaves. Two clinical patterns of disease were seen. Ponies given dried leaves collected after September 15 died by 18 hours, while ponies given dried leaves collected before September 15 became ill with a hemolytic syndrome and died by three to five days. Freshly harvested leaves administered immediately after collection did not produce disease in ponies, but when dried, they became toxic and remained so for at least 30 days. Overnight freezing did not alter the toxicity of the leaves. Leaves were toxic when administered at doses of 1.5 gm/kg of body weight. The clinical signs of ponies with the hemolytic syndrome included polypnea, tachycardia, icterus, cyanosis, scleral petechiation, and brownish discoloration of the urine and blood. Blood changes of ponies with the hemolytic syndrome included anemia, hemoglobinemia, Heinz bodies, depletion of erythrocyte reduced glutathione, increased erythrocyte fragility, and increased serum levels of aspartate amino transferase, sorbitol dehydrogenase, plasma protein, and bilirubin. Lesions of ponies that died from the hemolytic syndrome included icterus, centrilobular hepatic degeneration, hemoglobinemic nephrosis, and erythrophagocytosis by splenic, adrenal, and hepatic phagocytes. Only brownish discoloration of the blood and mild centrilobular hepatic degeneration were observed in the four ponies that died peracutely.