Hypertrichosis in a horse with alimentary T-cell lymphoma and pituitary involvement.

A 13-year-old Quarterhorse mare had a 6-month history of diarrhea, progressive weight loss, and lethargy. At presentation the mare was hirsute, had hyperhidrosis, and abnormal fat distribution in addition to severe diarrhea. A presumptive clinical diagnosis of protein-losing enteropathy and pituitary pars intermedia dysfunction was made. T-cell lymphoma was diagnosed in a rectal biopsy specimen. The owner elected to euthanize the mare because of poor prognosis and the severity of the disease. At necropsy, the mare had hypertrichosis and the pituitary gland was diffusely enlarged. Histologically, neoplastic lymphocytes infiltrated the gastrointestinal mucosa, mesenteric lymph nodes, and the pituitary gland. In addition, there was hyperplasia of the pituitary gland pars intermedia. Pituitary adenoma was not present. Hypertrichosis in this case could have been triggered by a combination of adenomatous hyperplasia of pars intermedia and lymphoma resulting in disruption of the hypothalamic dopaminergic tone or disruption of the hypothalamic thermoregulatory center.     

Primary sinonasal malignant melanoma with systemic metastasis in a non-gray horse

A 27-y-old Anglo-Arabian gelding with bay coat color was presented with a swelling of the left maxillary region. Fenestration on the left maxilla revealed that the left maxillary sinus was filled with black-red tissue. A portion of the tissue was excised and diagnosed histologically as malignant melanoma. Genotyping of the STX17 gene for gray coat color revealed that the horse did not have the “gray” factor. The horse was euthanized ~3 mo after first presentation. During autopsy, a black-to-gray mass extended from the left nasal cavity to the surrounding paranasal sinus and invaded the hard palate, cribriform plate, and the cranial portion of the left olfactory bulb. Moreover, identical black nodules were present in lymph nodes from the mandible to the larynx, and in the spleen, liver, kidney, and adrenal glands. However, masses were not found in the skin, perineal region, or pelvic cavity. All of the black-to-gray nodules were malignant melanomas that were histologically identical to the initial biopsy; tumor emboli were also found in the kidney. Sinonasal mucosal melanoma is a rare disease in horses.     

Primary liver disease in the horse

The clinical signs of liver disease are highly variable and non-specific. Irrespective of the cause or the duration of liver disease, more specific clinical signs, e.g. hepatic encephalopathy, become apparent in the advanced stages of the disease. Due to the non-specific clinical signs, the possible diagnosis of liver disease is frequently not taken into consideration. However, measurement of the plasma or serum concentrations of total bile acids and gamma glutamyl transferase (gamma GT) may provide valuable diagnostic information. The specific diagnosis can be confirmed by ultrasound examination of the liver and histological examination of a liver biopsy specimen. The most frequently documented liver diseases are acute hepatic necrosis, chronic hepatitis caused by pyrrolizidine alkaloids, cholelithiasis, and haemochromatosis. Immediate treatment with antibiotics and polyionic fluids, in association with supportive nutritional care, is usually necessary to maintain the horse until sufficient liver regeneration occurs to provide adequate function. The use of corticosteroids is contraindicated, except for patients with chronic active hepatitis. In some cases, e.g. portosystemic shunts or cholelithiasis, surgical intervention is indicated. Liver disease may be more common than is currently appreciated since little accurate information on the prevalence or incidence is available.     

Primary epitheliotropic intestinal T-cell lymphoma in a horse.

A 17-year-old Quarterhorse gelding with a clinical diagnosis of protein-losing enteropathy was submitted for necropsy following a 4-5-month duration of weight loss, decreased appetite, and hypoproteinemia. Gross findings included multiple 1-2-cm diameter ulcers on the luminal surfaces of the duodenum and ileum. Histologic examination revealed individual large, round cells infiltrating much of the mucosal epithelium of the duodenum, jejunum, ileum, and colon in addition to multifocal areas of ulceration. Similar round cells infiltrated Brunner's glands and expanded the submucosa beneath the foci of ulceration. Immunohistochemical staining indicated the round cell population was of T-lymphocyte origin. Several features of this equine neoplasm bear similarities to enteropathy-associated T-cell lymphoma in humans.     

Malabsorption in the horse associated with alimentary lymphosarcoma.

Three horses suffering from malabsorption were shown to have alimentary lymphosarcoma predominantly affecting the small intestine and the associated lymph nodes. The diffuse cellular infiltration in two of the case produced marked changes in the villous architecture reducing the available mucosal surface area, and, with lowered or barely detectable disaccharidase activities, contributed to the impairment of digestive-absorptive processes. One of the horses maintained a voracious appetite and was not diarrhoeic, but failed to gain weight, indicating differences in the production and utilisation of energy sources absorbed from the small and the large intestines. A large proportion of plasma cells in the infiltrate, and the resulting morphological changes in two of the cases bore a striking resemblance to features of alpha chain disease, an immunodeficiency disease of man, although immunological studies were not conducted on these horses.     

Gastric adenocarcinoma in a horse with portal vein metastasis and thrombosis: a novel cause of hepatic encephalopathy

A 17-year-old Quarter horse mare was referred to Cornell University for postmortem examination after 72 hours of encephalopathy that consisted of depression, mania, and blindness. A plasma sample and cerebral spinal fluid demonstrated hyperammonemia. Gross necropsy examination findings included the following: mild icterus, a transmural mass in the glandular portion of the gastric fundus, multiple masses throughout the liver, and a large tumor thrombus in the portal vein. Microscopically, the gastric mass, hepatic masses, and portal vein thrombus were composed of similar neoplastic epithelial cells that formed variably sized acini and branching cords separated by a dense desmoplastic stroma. Throughout the cerebral frontal cortex were numerous Alzheimer type II astrocytes. Hepatic encephalopathy was caused by gastric adenocarcinoma, with metastasis to the liver and the portal vein. The clinical and pathologic lesions from this unique case, as well as hyperammonemia and portal vein thrombosis in the pathogenesis of hepatic encephalopathy, are discussed.     

Intramuscular hemangiosarcoma with pulmonary metastasis in a horse

Intramuscular hemangiosarcoma resulting in severe anemia and thrombocytopenia was diagnosed in a 3-year-old Thoroughbred filly. Necropsy revealed multiple tumors within skeletal muscles and multiple pulmonary metastases.     

Bicavitary effusion in a horse with multicentric lymphoma

A 14-year-old Quarter Horse gelding presented for a 2-week history of increased respiratory rate, fever and weight loss. The referring veterinarian performed an ultrasonographic examination on the farm and considered a differential diagnosis of pleuritis and pleuropneumonia. On presentation, transtracheal wash showed suppurative septic inflammation with bacteria within macrophages. Thoracic ultrasonography showed increased hypoechoic fluid in the pleural and peritoneal cavities. Cytologic analysis of pleural and peritoneal fluids revealed lymphorrhagic effusion with atypical lymphocytes, suggestive of a lymphatic flow obstruction or lymphoma. Treatment consisted of drainage of the pleural fluid, anti-inflammatory agents, fluid therapy and antimicrobial therapy. Continued fluid accumulation in the thoracic cavity, tachypnoea, lack of response to pain medication and progressive lethargy resulted in the horse being subjected to euthanasia. At necropsy, bicavitary effusion was confirmed and histopathological diagnosis of multicentric lymphoma was made. Horses presenting with pleural effusion should also be evaluated for peritoneal effusion, as bicavitary effusion may indicate noninflammatory conditions such as neoplasia.     

Recurrent adnexal lymphoma in a horse

Lymphoma is a relatively uncommon neoplasm in the horse; however, it is considered the most common neoplasia of the equine haemolymphatic system. Limited reports of adnexal lymphoma have been documented in the literature, with no known reports of recurrence nearly a decade after mass excision. The objective is to describe a case of recurrent adnexal lymphoma in a 20-year-old Quarter Horse gelding presented to the Ophthalmology service at the University of Florida Veterinary Hospital (UFVH) for evaluation of a solitary subconjunctival mass of the right eye (OD). A focal, pink, fleshy mass associated with the dorsomedial bulbar conjunctiva was noted. An excisional biopsy was performed. Histopathology revealed lymphoma with clean margins. The client declined staging and further therapy at the initial visit. Approximately 8 years later, the horse began to exhibit intermittent mild to moderate diffuse swelling of the conjunctiva OD. Six months after onset, the swelling worsened acutely and was accompanied by severe swelling of the left conjunctiva (OS). The horse then returned to UFVH and was diagnosed with diffuse, bilateral conjunctival lymphoma. Humane euthanasia was elected. T cell lymphoma was confirmed with immunohistochemistry performed post-mortem. At necropsy, neoplastic tissue was observed throughout the adnexal and ocular tissues of both eyes and in the submandibular lymph nodes. Adnexal lymphoma is an uncommon neoplasm in the horse. To the authors’ knowledge, this is the first documentation of a nodular adnexal lymphoma that involved an 8-year period without recurrence followed by development of diffuse, bilateral disease. Typically, surgical excision of the nodular form of lymphoma involving the extraocular tissues yields an improved prognosis compared with the diffuse form of the disease. Further investigation is necessary to determine if nodular forms of adnexal lymphoma represent early stages of diffuse extraocular or systemic disease.     

Mediastinal lymphoma with complete atrioventricular block in a horse

A 15-year-old, neutered-male pony presented with a history of weight loss during 4 months. Clinical evaluation revealed severe bradycardia and complete atrioventricular block. At necropsy, a lobulated mass in the anterior mediastinum and moderate enlargement of the superficial cervical lymph nodes were observed. The vagus nerve and the brachiocephalic trunk were embedded in this anterior mediastinal tumor. Histologically, the mass was composed of sheets of neoplastic lymphoid cells expressing CD3, with a low mitotic rate. To the best of our knowledge, this is the first reported case of mediastinal lymphoma associated with complete atrioventricular block in horses.     

Pyogranulomatous lesion causing neurological signs localised to the sacral region in a horse

This case report describes neurological signs associated with a pyogranulomatous lesion within the sacral vertebral canal of a horse. The clinical findings included urinary overflow incontinence and reduced anal, perianal and tail tone. The horse failed to respond to medical management and a guarded prognosis for return to athletic performance initiated the decision for euthanasia.     

Cholelith causing duodenal obstruction in a horse.

A 10-year-old Appaloosa stallion was referred for evaluation of colic. At admission, the heart rate, capillary refill time, respiratory rate, and rectal temperature were high. Fifteen liters of reflux was obtained by nasogastric intubation. Palpation of an abdominal mass per rectum elicited signs of pain. At exploratory laparotomy, a mass was palpated in the ascending portion of the duodenum. The small intestine ruptured at the site of obstruction during manipulation. The horse was euthanatized. A large cholelith was the cause of the duodenal obstruction. At necropsy, multiple choleliths of various sizes were found in the pancreatic and common bile ducts and in the stomach.     

Malignant mast cell neoplasia with local metastasis in a horse

A 12-year-old Arab stallion was presented with a chronically swollen right carpus resulting in profound lameness of the same leg. An incisional biopsy of subcutaneous tissue from the right carpus submitted for cytology and histopathology revealed large numbers of eosinophils interspersed by substantial numbers of variably sized and granulated mast cells. Fungal culture of a subcutaneous tissue sample taken from the right carpus was negative. Serial full blood counts revealed persistent mature eosinophilia, not accompanied by a mastocytaemia, neutrophilia without left shift and persistent hyperfibrinogenaemia. After humane destruction, dissection of the affected limb revealed a thick layer of connective tissue deposited around the right carpal joint. Within the connective tissue were embedded many small 0.25-1 cm diameter yellow gritty nodules, which consisted of dystrophic calcification and necrotic cell debris. The tendons enveloped by the connective tissue mass had limited function. The right axillary lymph node was moderately enlarged, yellow-brown and moist. Histopathological examination revealed a moderately well differentiated mast cell neoplasm with evidence of metastasis to the regional lymph node. In horses, malignant mast cell neoplasia is rare, while metastasis has only been reported in one other horse. Eosinophilia associated with equine mast cell neoplasia has not been reported previously but is recorded in mast cell neoplasia in the dog.     

Presumed primary ocular lymphangiosarcoma with metastasis in a miniature horse

A 7‐year‐old, 153.0‐kg American Miniature mare presented for evaluation of keratoconjunctivitis of the right eye (OD). A superior palpebral conjunctival mass and stromal keratitis were diagnosed. The incisional biopsy diagnosis was a presumptive corneal hemangiosarcoma. Transpalpebral enucleation was performed, and histopathologic evaluation confirmed angiosarcoma of the conjunctiva, cornea, and extraocular muscles. The horse developed progressive epistaxis and orbital swelling following surgery. A systemic workup was performed 3 months after enucleation, revealing regrowth within the orbit and marked cranial cervical lymphomegaly, suggestive of metastasis. Humane euthanasia was performed, and necropsy confirmed a locally invasive periorbital tumor with metastasis to the submandibular tissue, submandibular lymph node, and thoracic inlet. Histopathologic evaluation of necropsy specimens revealed polygonal to spindle neoplastic cells lining neoplastic vascular channels lacking erythrocytes. Immunohistochemically, the neoplastic cells labeled strongly positive for PROX‐1, vimentin, CD‐31, VEGF, weakly positive for factor VIII‐related antigen, and negative for collagen IV. Based on the clinical, histological, and immunohistochemical features of this tumor, a primary ocular lymphangiosarcoma with metastasis was diagnosed.     

Parasites observed in the proximal alimentary tract of a Przewalski's horse in China

This article reports a Przewalski's horse from the Kalamaili Nature Reserve (KNR) in China transported to our institute to determine the cause of death. The animal had been subjected to necropsy before being transported to our institute; the entire digestive tract was removed but not opened to reduce the possible loss of parasites. During examination, ascarids in the intestines and bots in the oral cavity and stomach were observed. The parasites were identified according to an identification key and enumerated. The ascarids were identified as Parascaris spp. and were associated with a volvulus, resulting in intestinal obstruction. A total of two (stomach), one (duodenum) and 106 (intestines) Parascaris spp. were counted. Bots in the digestive tract were identified as third stage larvae of Gasterophilus pecorum (G. pecorum), Gasterophilus nigricornis (G. nigricornis) and Gasterophilus nasalis (G. nasalis), which may have been associated with stomach ulcers suffered by the horse. Attached to the lining of the oral cavity and stomach were 331 and 2014, respectively, larvae of G. pecorum, while in the duodenum there were 23 third stage larvae of G. nigricornis and 20 third stage larvae of G. nasalis. Therefore, the possibility of the presence of these parasites should not be overlooked in Przewalski horses as these parasites may be responsible for severe clinical signs in infected animals.