The clinical and pathologic findings are reviewed for 14 horses with metastatic melanoma. All were older gray horses, with an average age of 16 years. The most common sites of primary tumors were the ventral tail, perineum, and parotid salivary gland. Metastases were found in multiple locations and caused a variety of clinical syndromes. The most common sites for metastases were the lymph nodes, liver, spleen, skeletal muscle, lungs, and surrounding or within blood vessels throughout the body. Many of the horses had dermal melanomas for years (range 1-6 years) before succumbing to metastatic disease. Histologic characteristic of dermal masses was not predictive of malignancy in the majority of cases. Treatment consisting of surgical debulking and administration of cimetidine, an autogenous vaccine, or both was attempted in 4 horses with no effect on outcome.

The clinical and pathologic findings are reviewed for 14 horses with metastatic melanoma. All were older gray horses, with an average age of 16 years. The most common sites of primary tumors were the ventral tail, perineum, and parotid salivary gland. Metastases were found in multiple locations and caused a variety of clinical syndromes. The most common sites for metastases were the lymph nodes, liver, spleen, skeletal muscle, lungs, and surrounding or within blood vessels throughout the body. Many of the horses had dermal melanomas for years (range 1-6 years) before succumbing to metastatic disease. Histologic characteristic of dermal masses was not predictive of malignancy in the majority of cases. Treatment consisting of surgical debulking and administration of cimetidine, an autogenous vaccine, or both was attempted in 4 horses with no effect on outcome.Key words: Dermal melanocytosis; Horse; Neoplasia; Perineum; Tumor.M elanomas, with a prevalence of 4-15%, are common skin tumors of horses. 1 The true incidence may be higher because these tumors are easily identified and infrequently submitted for histologic examination. Many reports have estimated that as many as 80% of older gray horses will develop dermal melanomas, with the majority of these masses being benign.1,2 The statement also has been made that many of these histologically benign dermal melanomas may eventually metastasize and thus should be considered potentially malignant.1,2 The true incidence of metastatic melanoma in horses is unknown. Over the time period of the study (1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001), 101 horses were diagnosed with cutaneous melanomas at our hospital. The prevalence of metastatic melanoma in this population was approximately 14%. However, given the infrequency with which these tumors are submitted for a histologic diagnosis, the true prevalence of metastatic melanomas may be less. The purpose of this study was to describe the clinical and histologic characteristics of metastatic melanoma in 14 horses. Materials and MethodsMedical records for horses admitted to the teaching hospital and to the necropsy service were examined over an 11-year period. Horses with a histologically confirmed melanoma present in a location other than the epidermis were included in the study. Patient records were reviewed and signalment, presenting complaint, clinical signs, previous treatment, response to treatment, and pathologic findings were recorded. The age distribution for cases was compared to the age distribution of the general hospital population by using chi-squared analysis with a significance level of P Յ .05.A gross postmortem examination was performed on all 14 horses. The brain and spinal cord were evaluated in 11 of the 14 horses. For histopathology, tissue samples not thicker than 1 cm were fixed for 4-10 days in 10% buffered formalin. Tissue samples were reduced, placed in histology cassettes, and progressively dehydrated in alcohol From the Department of Clinical Studies (MacGillivray, Swe...

Background: The renin-angiotensin-aldosterone system (RAAS) and hypothalamic-pituitary-adrenal axis (HPAA) and their interactions during illness and hypoperfusion are important to maintain organ function. HPAA dysfunction and relative adrenal insufficiency (RAI) are common in septic foals. Information is lacking on the RAAS and mineralocorticoid response in the context of RAI in newborn sick foals.Objectives/Hypothesis: To investigate the RAAS, as well as HPAA factors that interact with the RAAS, in hospitalized foals, and to determine their association with clinical findings. We hypothesized that critical illness in newborn foals results in RAAS activation, and that inappropriately low aldosterone concentrations are part of the RAI syndrome of critically ill foals.Animals: A total of 167 foals 3 days of age: 133 hospitalized (74 septic, 59 sick nonseptic) and 34 healthy foals. Methods: Prospective, multicenter, cross-sectional study. Blood samples were collected on admission. Plasma renin activity (PRA) and angiotensin-II (ANG-II), aldosterone, ACTH, and cortisol concentrations were measured in all foals.Results: ANG-II, aldosterone, ACTH, and cortisol concentrations as well as ACTH/aldosterone and ACTH/ cortisol ratios were higher in septic foals compared with healthy foals (P < .05). No difference in PRA between groups was found. High serum potassium and low serum chloride concentrations were associated with hyperaldosteronemia in septic foals.Conclusions and Clinical Importance: RAAS activation in critically ill foals is characterized by increased ANG-II and aldosterone concentrations. Inappropriately low cortisol and aldosterone concentrations defined as high ACTH/cortisol and ACTH/aldosterone ratios in septic foals suggest that RAI is not restricted to the zona fasciculata in critically ill newborn foals.

Background: Disorders of calcium regulation are frequently found in humans with critical illness, yet limited information exists in foals with similar conditions including septicemia. The purpose of this study was to determine whether disorders of calcium exist in septic foals, and to determine any association with survival.Hypothesis: Blood concentrations of ionized calcium (Ca

SummaryReasons for performing the study: Hypothalamic-pituitary-thyroid (HPT) axis dysfunction is associated with morbidity and mortality in critically ill people. To date, investigations of HPT axis in critically ill foals are limited. Objectives: To document the occurrence of low thyroid hormone concentrations (presumptive nonthyroidal illness syndrome; NTIS) in critically ill newborn foals and investigate whether NTIS is associated with severity of disease and outcome. Hypothesis: NTIS occurs frequently in foals with sepsis and is associated with sepsis score and outcome. Reverse T3 (rT3) concentrations will be increased in septic foals and highest in nonsurvivors. Methods: Thyroid hormones (total and free thyroxine [TT4 and fT4], total and free tri-iodothyronine [TT3 and fT3], reverse T3 [rT3]) were prospectively measured in healthy, sick nonseptic and septic foals. Clinical and laboratory information was retrieved from the medical records. Hormones were measured by validated radioimmunoassays. Results: Concentrations of all thyroid hormones except rT3 (P = 0.69) were decreased in septic and sick nonseptic foals (P<0.01). Reductions in hormone concentrations were associated with an increased sepsis score (P<0.01). Nonsurviving septic foals had lower TT4, fT4, TT3 and fT3 concentrations than surviving septic foals (P<0.01). rT3 concentrations were higher in nonsurviving septic premature foals than surviving septic premature foals (P<0.05). Conclusions: NTIS (euthyroid sick syndrome) is frequently observed in critically ill and premature foals, and associated with severity of disease and mortality. Potential relevance: More research is needed to better understand the mechanism of this finding and determine whether manipulation of the HPT axis or thyroid replacement therapy could be beneficial.