D. W. Hayden

Immunohistochemical morphometry of pancreatic endocrine cells in diabetic, normoglycaemic glucose-intolerant and normal cats

The anatomical distribution and volume fractions of pancreatic A cells (glucagon), B cells (insulin) and D cells (somatostatin) were evaluated by an immunoperoxidase technique in 6 diabetic cats, 6 normoglycaemic glucose-intolerant cats and 6 normal control cats. Islets lacking A cells were observed in some sections from the right lobe of the pancreas which correlated with a significantly lower A cell volume fraction in the right pancreatic lobe. Endocrine cell volume fractions in normoglycaemic glucose-intolerant cats were not significantly different from controls. Thus, a reduction in B cell volume fraction was not necessary for the occurrence of impaired glucose tolerance in these cats. However, the reduction of B cell volume fraction in the 2 normoglycaemic glucose-intolerant cats with insular amyloidosis may in part explain the more severely impaired glucose tolerance previously observed in these cats. Insular amyloidosis in our feline diabetics, as in human type II diabetics, was associated with a significant decrease in A and B cell volume fractions. In both human type II and feline diabetes mellitus, however, the reduction in B cell mass does not appear sufficient alone to lead to diabetes mellitus. Therefore, amyloid replacement of functional endocrine cells does not appear to be the primary diabetogenic event in feline diabetes mellitus, but may contribute to progression of the condition due to loss of functional B cell reserves. We thus postulate that a B cell defect precedes deposition of islet amyloid and that these amyloid deposits may thus provide an important biochemical clue to specific B cell derangements occurring in adult-onset diabetics.

Feline insular amyloid: association with diabetes mellitus.

Of 31 domestic cats with diabetes mellitus, 20 (65%) had amyloid deposits in their pancreatic islets (i.e., insular amyloid). The incidence of insular amyloidosis (p = 0.34) was not significantly different between diabetic and age-matched, non-diabetic cats from our previous study. Diabetic cats, however, had a significantly higher mean percentage of islets with amyloid (p = <.005) and a significantly higher mean percentage of islets with abundant amyloid deposits (p = <005) than did non-diabetic cats. These results suggest that insular amyloidosis and diabetes are causally related and are not simply concurrent diseases associated with aging. Although the specific relationship of insular amyloidosis to the pathogenesis of diabetes mellitus was not determined, a functional islet cell abnormality probably precedes the diabetic state and the deposition of insular amyloid.

Morphologic Changes in the Mammary Gland of Megestrol Acetate-treated and Untreated Cats: A Retrospective Study

Abnormal mammary gland growth is a side effect of progestin therapy in some cats. In this retrospective study, the nature and significance of morphologic changes in the mammary gland of 17 megestrol acetate (MA)-treated cats were compared to mammary lesions in 97 untreated cats. Fourteen out of 17 MA-treated cats had non-neoplastic mammary lesions including fibroepithelial hyperplasia (nine cats), lobular hyperplasia (three cat), and duct ectasia (two cats); whereas three MA-treated cats had mammary neoplasms including one adenoma and two carcinomas. Although MA has been causally linked to mammary cancer in cats, only mammary fibroepithelial hyperplasia was clearly associated with MA therapy in this study. Fibroepithelial hyperplasia occurred in older (average age 8.1 years) neutered male and female cats in the MA-treated group and in younger (average age 2.1 years) female cats in the untreated group. Morphologically, both intraductal and solid fibroepithelial growth patterns were seen. Intraductal fibroepithelial hyperplasia was further subdivided into papillary and circumferential types. An apparent greater association between MA therapy and the intraductal types of fibroepithelial hyperplasia was noted. Furthermore, it appears likely that mammary lobular byperplasia also is linked to MA therapy. Possible mammatrophic effects of MA and other growth-promoting agents in the cat are discussed.

High dose intravenous glucose tolerance test and serum insulin and glucagon levels in diabetic and non-diabetic cats: relationships to insular amyloidosis.

The high dose intravenous glucose tolerance test and concurrent immunoreactive serum insulin and glucagon levels were measured and the results related to the presence or absence of pancreatic insular amyloid in 16 cats, seven of which were known to be diabetic. Control values for all parameters were established using seven additional clinicopathologically normal cats. Nine of the 16 cats had normal fasting blood glucose levels (less than 120 mg/dl) and impaired glucose tolerance. These cats had attenuated (3/9) or normal (6/9) 0 to 5 minute glucose-stimulated insulin secretion, rising 45 to 60 minute insulin secretion (7/9), low mean insulin/glucose ratio, and normal mean serum glucagon. Three of the nine cats with impaired glucose tolerance had insular amyloidosis. These three cats had significantly higher mean blood glucose levels during the glucose tolerance test than did cats with impaired glucose tolerance and no insular amyloid deposits. Also, these three cats accounted for three of the four longest glucose disappearance one-half times (T 1/2 s), three of the four lowest glucose disappearance coefficients, and three of the four lowest 0 to 5 minute insulin responses. The seven diabetic cats (fasting blood glucose levels greater than 120 mg/dl) had either low to low normal (6/7) or above normal (1/7) fasting insulin levels, no insulin response to intravenous glucose stimulation (6/7), and elevated mean serum glucagon levels. Insular amyloid was present in six of the seven diabetic cats. Three diabetic cats with marked insular amyloid deposits had glucose disappearance T 1/2 and K (coefficient) values, serum insulin levels, serum glucagon levels, and insulin/glucose ratios which were not significantly different from the other three diabetic cats with slight to moderate insular amyloidosis. These results confirm a strong association between the occurrence, but not the extent of insular amyloidosis and diabetes mellitus in adult diabetic cats, although amyloid replacement of pancreatic islets does not appear to be the primary diabetogenic event. Rather, these results appear to be consistent with our hypothesis that insular amyloid deposition is a morphologic marker of primary B-cell dysfunction that is basic to the pathogenesis of the diabetic condition, and is reflected clinically by impaired glucose tolerance.

Disseminated Malignant Histiocytosis in a Golden Retriever: Clinicopathologic, Ultrastructural, and Immunohistochemical Findings

Diagnosis of malignant histiocytosis (MH), a disorder characterized by systemic proliferation of morphologically atypical histiocytes and their precursors, in an 8-year-old neutered female Golden Retriever was based on light and electron microscopic and immunohistochemical findings. Clinically, the dog presented with unilateral forelimb lameness. Eight days after surgical exploration of a swollen brachium, the dog developed sudden onset of posterior paresis, fecal and urinary incontinence, and a flaccid tail. Necropsy revealed infiltrative and nodular lesions in the right forelimb and regional lymph nodes, thoracic and abdominal cavities, and lumbar epidural space. Gross lesions were not found in the lungs or integument. Histopathologic examination showed infiltrates of atypical histiocytes in skeletal muscle, joint, and regional lymph nodes of the right forelimb; intercostal muscle; lung; liver; spleen; pancreas; kidneys; and spinal dura. Most tumor infiltrates were nodular and composed of loosely aggregated cells that were 10-30 μm in diameter with abundant eosinophilic to foamy cytoplasm, had central or eccentric nuclei, and were periodic acid-Schiff negative. Many binucleated cells, multinucleated giant cells, and mitotic figures were seen. Tumor cells contained phagocytosed erythrocytes, mononuclear cells, and some leukocytes. Ultrastructural features of tumor cells included cytoplasmic lipid droplets, lysosomes, and phagolysosomes. Immunohistochemical studies on paraffin-embedded sections showed positive reactivity to human T-cell Ag (clone UCHL-1) and for lysozyme, α-1-antitrypsin, and cathespin B. Polyclonal intracellular immunoglobulin reactivity and lectin binding (peanut, soybean, and wheat germ agglutinins and concanavalin A) were also demonstrated. Criteria for diagnosis of malignant histiocytic tumors and differential diagnosis are discussed.

Prostatic intraepithelial neoplasia in dogs with spontaneous prostate cancer

Prostatic intraepithelial neoplasia (PIN) is the most likely precursor of human prostate cancer. The prevalence and immunophenotype of PIN in dogs with spontaneous prostate cancer has not been previously described. To investigate the association between PIN and prostate cancer, we evaluated the prostates of dogs with spontaneous prostate carcinoma. The prevalence of PIN was determined in formalin‐fixed prostates from 29 dogs with spontaneous prostate cancer. Using immunoperoxidase techniques, we compared basal cell layer integrity (high molecular weight keratin 34 beta‐E12), proliferative index (MIB‐1), and microvessel density (Factor VIII‐related antigen) in 14 prostates which contained benign epithelium, PIN, and carcinoma. PIN was present in 19 of 29 (66%) prostates from dogs with spontaneous prostate cancer. The basal cell layer was intact in benign epithelium, disrupted in 72% of acini with PIN, and absent in carcinoma. The mean proliferative index was 17%, 25%, and 40% for benign epithelium, PIN, and carcinoma, respectively, and these differences were significant. The mean microvessel density in foci of PIN and carcinoma (32 and 39 vessels per mm2, respectively) was greater than in benign epithelium (23 vessels per mm2). High‐grade PIN is common in the prostates of dogs with spontaneous carcinoma. The basal cell layer is partially disrupted in PIN, whereas it is absent in prostate cancer. The proliferative index and microvessel density of PIN are intermediate between benign epithelium and cancer. These results are similar to those reported for human PIN and prostate cancer, and indicate that PIN is part of a morphologic continuum in the progression of prostate cancer. To our knowledge, this is the first description of high‐grade PIN spontaneously occurring in animals. The canine prostate may serve as a useful model for examining factors that modulate PIN and prostate cancer progression. Prostate 30:92–97, 1997.

Canine Pancreatic Endocrine Tumors: Immunohistochemical Analysis of Hormone Content and Amyloid

Thirty-one primary canine pancreatic endocrine tumors and their metastases were studied histologically and immunohistochemically for the presence of insulin, glucagon, somatostatin, pancreatic polypeptide (PP), gastrin, and adrenocorticotrophic hormone (ACTH). Tumors were also evaluated for the presence of amyloid. The cytoarchitectural pattern of 25 of 31 primary tumors was predominantly solid, whereas three tumors were mostly glandular, two were unclassified, and one had a gyriform pattern. Cells with insulin immunoreactivity were found in 30 of 31 tumors and were found in all cases in which there was clinical evidence of inappropriate insulin secretion. Insulin was the only hormone demonstrable in three of the 30 tumors, but cells immunoreactive for other hormones were also present in various combinations in most tumors [i.e., glucagon (13 of 30), somatostatin (17 of 30), PP (25 of 30), and gastrin (2 of 30)]. One tumor contained only cells with glucagon and PP immunoreactivity. Amyloid was found in ten of 31 primary tumors but was not detected in metastases. Cells with insulin immunoreactivity were the only cell type consistently present in tumors containing amyloid. Amyloid deposits did not immunoreact with any of the antisera. Seventeen of 31 dogs had metastasis of the pancreatic endocrine tumor to regional lymph nodes, liver, or both. All metastases available for study (15 of 17) contained cells with insulin immunoreactivity and some contained cells with PP or somatostatin immunoreactivity. No statistically significant (P > 0.05) differences in tendency to metastasize were found when pancreatic endocrine tumors were compared by region of origin, cytoarchitectural pattern, presence of amyloid, or by number of hormones contained within the tumor.

Comparison of Histopathologic Criteria and Skeletal Muscle Fixation Techniques for the Diagnosis of Polysaccharide Storage Myopathy in Horses

The purpose of the study reported here was to determine the effect of three methods of fixation of skeletal muscle biopsy specimens on the histopathologic appearance of muscle sections and to determine criteria that were most consistently associated with a diagnosis of polysaccharide storage myopathy (PSSM) in horses. Surgically excised semimembranosus muscle biopsy specimens were obtained from nine horses previously diagnosed with PSSM and from 15 control horses. Portions of each specimen were fixed in formalin, frozen immediately, and chilled for 24 hours prior to freezing. Sections stained with hematoxylin and eosin (HE), periodic acid-Schiff (PAS), and amylase-PAS were scored for histopathologic criteria by three investigators blinded to the sample origin. The presence of amylase-resistant, abnormal polysaccharide was found to be the most sensitive and specific diagnostic indicator for PSSM, and was readily detected regardless of the fixation technique or investigator. Other less-specific features associated with PSSM included atrophy and cytoplasmic and subsarcolemmal vacuoles; however, their histologic scores varied among fixation technique and investigators. Scores for subsarcolemmal and cytoplasmic amylase-sensitive glycogen in horses with PSSM were similar to those for control horses and varied among fixation techniques. In conclusion, PSSM is most accurately diagnosed in muscle biopsy specimens on the basis of appearance of amylase-resistant, abnormal polysaccharide, not amylase-sensitive glycogen, regardless of fixation technique. In general, frozen sections appeared to be better suited for studying myopathies because many histopathologic features of skeletal muscle were obscured by formalin fixation.

Pyogranulomatous meningoencephalitis associated with dematiaceous fungal (Cladophialophora bantiana) infection in a domestic cat.

A 6-month-old, castrated male domestic cat with progressive neurological signs of 2–3 weeks duration was necropsied. Macroscopic findings were restricted to the brain and included irregularly shaped, well-delineated but unencapsulated areas of intense black pigmentation involving the rostral portion of both cerebral hemispheres. Microscopically, numerous brown, oblong, segmented branching hyphae and conidial-like structures and extensive pyogranulomatous inflammation were identified throughout the cerebral lesion and in adjacent blood vessels. Hyphae and oval conidia were best demonstrated with either Gomori methenamine silver or periodic acid–Schiff stain. Fungal infection in the brain of this cat was unrelated to any concurrent immunodeficiency syndrome or immunosuppressive treatment. This report deals with a case of cerebral phaeohyphomycosis from which a different species of dematiaceous fungus, Cladophialophora bantiana, was isolated and identified.

Feline Insular Amyloid: Incidence in Adult Cats with No Clinicopathologic Evidence of Overt Diabetes Mellitus

Pancreatic tissues from 93 adult domestic cats with no clinicopathologic evidence of overt diabetes mellitus were examined for islet amyloid. Amyloid deposits were found in the pancreatic islets of 44 cats. Approximately one-third of these deposits were not seen with HE, but subsequently were identified with Congo red stain. The proportion of islets with amyloid, the intra-islet location of amyloid, and the amount of amyloid in individual islets also were characterized. In this select population of adult cats, the presence or absence of islet amyloid was not linked significantly (p = > 0.05) to age, breed, sex or primary anatomic diagnosis. Results of this study indicate that: the incidence of islet amyloid in cats is higher than previously recognized; as in man, islet amyloid can occur in cats without concurrent overt diabetes mellitus; and islet amyloid should not be considered pathognomonic for diabetes mellitus.