An 8-year-old 46.3-lb (21-kg) female spayed mixed-breed dog was referred to the Purdue University Veterinary Teaching Hospital for evaluation of lethargy, inappetence, weight loss, and alopecia of several months' duration.
An 8-year-old 46.3-lb (21-kg) female spayed mixed-breed dog was referred to the Purdue University Veterinary Teaching Hospital for evaluation of lethargy, inappetence, weight loss, and alopecia of several months' duration (Figure 1).
1. An 8-year-old mixed-breed dog with inappetence, weight loss, and alopecia.
At presentation, the dog was in poor body condition, with a score of 3/9. The dog's temperature and pulse and respiration rates were normal. The physical examination revealed erythema, ulcers, and superficial excoriations involving the footpads (Figure 2) and ventral interdigital areas, extending to the tarsus and carpus. Similar lesions were noted on the elbows, hocks (Figure 3), ears, and commissures of the mouth. No other abnormalities were identified on oral examination, abdominal palpation, or thoracic auscultation.
2. Erythema, ulcers, and superficial excoriations on the dog's footpad.
Differential diagnoses considered at this point included various autoimmune, hypersensitivity, and paraneoplastic dermatitides; erythema multiforme; toxic epidermal necrolysis; various cutaneous neoplasms; canine distemper-associated hyperkeratosis; and nutritional disorders such as zinc deficiency.
3. Erythema and crusty alopecia on the dog's dorsal paw, tarsus, hock, and stifle region.
Histologic examination of biopsy samples from the footpads and adjacent haired skin revealed severe, chronic, and regionally diffuse acanthosis with intracellular edema in the stratum spinosum, parakeratosis and crusting, and superficial lymphohistiocytic dermatitis, suggestive of superficial necrolytic dermatitis and glucagonoma-associated paraneoplastic syndrome (Figure 4). A radiographic examination revealed slightly decreased liver and cardiac silhouettes but no abdominal masses. An ultrasonographic examination did not reveal any space-occupying abdominal masses or abnormal hepatic echotexture.
4. A photomicrograph of a footpad biopsy showing parakeratotic hyperkeratosis, acanthosis, and superficial lymphohistiocytic dermatitis. Note the red upper layer of the stratum compactum (short arrow), the white middle layer of ballooning degeneration in the stratum spinosum (arrowhead), and the blue hyperplastic basal cell layer of the epidermis (long arrow) (hematoxylin-eosin stain, 100X).
To explore possible causes of the superficial necrolytic dermatitis, such as hepatic deficiency or a pancreatic glucagonoma, fasting blood samples were submitted for a complete blood count (CBC), serum chemistry profile, and plasma glucagon concentration. A bile acid assay was also done. The CBC did not reveal any clinically relevant hematologic abnormalities, and the serum chemistry profile revealed only mildly decreased blood urea nitrogen (4 mg/dl; reference interval = 5 to 28 mg/dl) and creatinine (0.4 mg/dl; reference interval = 0.5 to 1.5 mg/dl) concentrations, attributed to the poor body condition score and associated reduced muscle mass. Hepatic enzyme activities and serum preprandial and postprandial bile acid concentrations were normal.
Urinalysis of a sample obtained by cystocentesis revealed hematuria and bacteriuria (2+ blood, 1+ bacteria, > 50 RBCs/hpf, and 5 WBCs/hpf), indicating bacterial cystitis. A urine bacterial culture was positive for Escherichia coli, with a wide spectrum of antibacterial sensitivity.
Plasma samples analyzed for glucagon concentration by using a human radioimmunoassay at The Ohio State University Medical Center revealed plasma glucagon concentrations greater than 1,700 ng/L (canine reference interval = 35 to 49 ng/L).1
The physical examination findings and histopathologic changes were consistent with superficial necrolytic dermatitis, and the plasma glucagon concentration strongly suggested that a glucagon-secreting pancreatic tumor was present. An exploratory laparotomy was scheduled for 18 days after presentation. The dog's bacterial cystitis was treated.
After routine intravenous anesthetic induction, intubation, and establishment of a surgical plane of anesthesia with isoflurane, a ventral midline laparotomy was performed. A 1-cm diameter multilobular mass was identified on the caudal pole of the right lobe of the pancreas. The mass was removed (Figure 5) and submitted for cytologic and histologic evaluation. Postoperative recovery was uneventful.
5. The surgically removed mass and adjacent pancreatic tissue from the caudal pole of the right lobe of the pancreas (the hemostat tip is adjacent to the mass).
The cytologic examination revealed that the scrapings of the pancreatic mass were highly cellular. The scrapings consisted primarily of individual and small cohesive groups of neoplastic mononuclear cells mixed with many cell-free nuclei and erythrocytes (Figure 6). The mononuclear cells also had round nuclei with coarsely stippled nuclear chromatin, and many of the cells had a single, small prominent nucleolus. The mononuclear cells also had moderate amounts of light-blue to gray, indistinct cytoplasm; mild anisocytosis, anisokaryosis, and a variation in the nuclear:cytoplasmic ratios were present. A few small cohesive clusters of exocrine pancreatic glandular epithelial cells and low to moderate numbers of cytologically normal small lymphocytes were also identified. The scrapings were cytologically consistent with an endocrine neoplasm.
6. Cytologic examination of a scraping from the pancreatic mass revealed a monomorphic population of neoplastic mononuclear cells in small cohesive groups with many cell-free nuclei typical of an endocrine neoplasm (modified Wright's stain, 500X).
The histologic examination revealed that the section of pancreatic tissue consisted of a single, approximately 0.6-cm diameter, nonencapsulated, poorly delineated neoplastic mass that had infiltrated the adjacent normal exocrine pancreatic glandular tissue (Figure 7). The nodule was composed of round to polygonal neoplastic cells with lightly basophilic granular cytoplasm and round to slightly oval vesicular nuclei with a single prominent nucleolus (Figure 8). Mild anisocytosis, anisokaryosis, and a variation in the nuclear:cytoplasmic ratios were present. Mitotic figures were not seen, and no obvious vascular invasion was identified. A mild, multifocal lymphohistiocytic inflammatory infiltrate within the tumor was also identified. Small groups of atrophic exocrine pancreatic glandular epithelial cells were trapped within the neoplastic mass. The histologic examination results were consistent with a pancreatic islet cell tumor. The dog's prognosis was poor because of the local invasion.
7. Histologic examination of tissue from the resected pancreatic mass revealed a discrete population of pale uniform neoplastic cells adjacent to normal exocrine pancreatic glandular tissue (upper left and entrapped within the neoplasm) (hematoxylin-eosin stain, 100X).
The results of an immunohistochemical analysis performed at The University of Minnesota showed that the neoplastic cells were immunoreactive for insulin, glucagon, and islet amyloid polypeptide. No neoplastic cells stained positively for pancreatic polypeptide, somatostatin, or gastrin. These findings indicated that the pancreatic islet cell tumor was best characterized as a glucagonoma of alpha pancreatic islet cell origin.
8. Histologic examination of tissue from the resected pancreatic mass revealed round to polygonal neoplastic cells with lightly basophilic granular cytoplasm and round to slightly oval vesicular nuclei with single prominent nucleoli, consistent with a pancreatic islet cell tumor (hematoxylin-eosin stain, 400X).
Three weeks after the surgery, the dog's clinical condition improved. The skin lesions resolved, and the dog's appetite and attitude returned to normal. However, seven months after the surgery, the dog returned to Purdue for reevaluation because of anemia, anorexia, and vomiting. Because of the owner's financial constraints and the dog's poor clinical condition, the owner elected euthanasia.
A blood sample was obtained before euthanasia, and the dog's plasma glucagon concentration was 216 ng/L. Necropsy results showed no gross evidence of glucagonoma metastases or other primary neoplasia. A histologic examination of tissues from necropsy (pancreas, liver, kidney, spleen, adrenal glands, gastrointestinal tract, heart, lung, bone marrow) revealed splenic extramedullary hematopoiesis, mild and multifocal hepatocellular vacuolar degeneration, and cholestasis. The gross necropsy results and histologic findings did not provide an explanation for the clinical signs or elevated glucagon concentration.
Islet cell tumors, uncommon neoplasms of neuroendocrine cells within the pancreas, are classified as insulinomas, glucagonomas, gastrinomas, or somatostatinomas, depending on the predominant hormone secreted by the neoplasm.2 About 200 cases in people have been reported.2-4 A few cases of glucagonomas in dogs have been reported, but the cytologic and histologic examination results have not been reported together.5-11
About 50% of the islet cell tumors in people are immunohistochemically reactive for multiple hormones. These tumors can secrete any of the hormones known to be present in the pancreatic islets, including insulin, glucagon, somatostatin, pancreatic polypeptide, and gastrin, either singly or in any combination.12 However, a single cell type and pancreatic hormone generally predominate and usually result in the corresponding metabolic syndrome.12 This ability to produce multiple hormones is also found in canine islet cell tumors.6,12,13
In people, glucagonomas are neoplasms of alpha cells that result in a paraneoplastic disease characterized by necrolytic migratory erythema, diabetes mellitus, weight loss, anemia, glossitis, stomatitis, thromboembolism, and gastrointestinal and neuropsychiatric disturbances. These clinical findings along with hyperglucagonemia and a pancreatic islet cell tumor establish the diagnosis.
The hallmark clinical finding in people with a glucagonoma is necrolytic migratory erythema. The skin lesions have a predilection for the perioral region, perineum, lower abdomen, thighs, buttocks, and distal extremities. In all the reported cases of glucagonomas in dogs, skin lesions were also a primary complaint.5,8
In dogs, the skin lesions are most commonly identified on the footpads, elbows, hocks, face, ventral abdomen, and perineum. The terms superficial necrolytic dermatitis, metabolic epidermal necrosis, diabetic dermatosis, hepatocutaneous syndrome, and necrolytic migratory erythema have been used to describe the skin lesions in dogs.5,6,8-11,14 Unlike necrolytic migratory erythema in people, superficial necrolytic dermatitis in dogs appears to occur most commonly with a hepatopathy (hepatocutaneous syndrome) and less commonly with a glucagon-secreting tumor.15
Histologic features. In people, the skin lesions include parakeratotic hyperkeratosis and moderate epidermal hyperplasia associated with intracellular edema of the upper portion of the stratum spinosum. The lesions create distinctive layers: intensely eosinophilic, keratinous cellular debris superficially; pale-staining edematous keratinocytes in a middle layer; and a deep zone of basophilic hyperplastic basal cells. Similar histologic changes have been identified in dogs with glucagon-secreting neoplasms or hepatic disease (hepatocutaneous syndrome). Because the characteristic lesions are not seen in every punch biopsy sample from an affected patient, three to five biopsies are recommended.
Pathogenesis. In people, the pathogenesis of the skin disease is thought to be an indirect result of chronically elevated plasma glucagon concentrations. The high glucagon concentrations promote amino acid mobilization in tissues because of the need for substrate in prolonged gluconeogenesis.3 Glucagon's subsequent activation of the urea cycle enzymes carbamoyl-phosphate synthase and argininosuccinate synthase promotes the catabolism of amino acids. These pathways of protein degradation are hypothesized to cause hypoaminoacidemia, which causes cellular necrosis in the epidermis by depleting epidermal proteins.2 Liver disease along with fatty acid and zinc deficiencies may also contribute to the pathogenesis of the skin lesions in some cases.2
A similar pathogenesis may exist for superficial necrolytic dermatitis in dogs. Serum amino acid concentrations were determined in three of the eight reported cases, and 20 of 24, 13 of 18, and four of five amino acids tested were found to be decreased.5 Amino acid concentrations were not determined in this case.
Hyperglycemia or glucose intolerance in association with diabetes mellitus has been reported in people with glucagon syndrome and in some dogs with glucagonomas.2,5,15 Diabetes mellitus is hypothesized to be due to glucagon's diabetogenic actions.2 However, the development of diabetes mellitus most likely depends on the glucagon:insulin ratio, the relative proportion of other hyperglycemic hormones, and the pre-existing genetic tendency toward glucose intolerance.2 In this case report, the patient had no evidence of concurrent diabetes mellitus.
Other nonspecific clinical signs associated with glucagonomas in dogs include normocytic normochromic nonregenerative anemia and weight loss.2 When present, anemia can be explained by the suppression of bone marrow erythropoiesis (i.e. anemia of chronic disease) induced by the neoplasm, and the weight loss is a result of glucagon's catabolic effects.4
The hallmark laboratory finding in people with glucagonomas is elevated fasting serum glucagon concentrations. High metastatic rates are also commonly associated with glucagonomas in people.2
As in this case report, glucagon concentrations were markedly elevated in seven of nine previously reported cases in dogs.5,8 A pancreatic mass was identified in seven of the nine canine glucagonoma cases; however, in two dogs, a primary pancreatic tumor was not identified. The diagnosis of glucagonoma in those two dogs was reached by demonstrating glucagon immunoreactivity in hepatic metastases.5,10 Metastases were identified in five of the nine cases, most frequently involving the liver and the mesenteric or hepatic lymph nodes. In this dog, at the time of euthanasia, no metastatic disease was found despite the plasma glucagon concentration's being above the published canine reference interval, suggesting local or metastatic tumor growth.
Similar to this case and to cases in people, all previously reported cases of canine glucagonoma were immunoreactive for glucagon, either singly or in combination with insulin, somatostatin, islet amyloid pancreatic polypeptide, or pancreatic polypeptide. This finding underscores the importance of plasma glucagon concentrations in reaching a definitive diagnosis of glucagonoma and glucagonoma-associated paraneoplastic skin disease.
Although glucagonomas are uncommon tumors in veterinary medicine, they should be considered as a differential diagnosis in any patient exhibiting clinical and histologic changes consistent with superficial necrolytic dermatitis. A diagnosis of glucagonoma should be based on elevated plasma glucagon concentrations and a confirmed neuroendocrine pancreatic tumor. In addition, the characteristic cutaneous changes are strongly suggestive of the disease. Immunohistochemical analysis of tumor tissue is a helpful diagnostic tool; however, it is limited by the ability of many islet cell tumors to produce multiple hormones. Thus, plasma glucagon concentrations are necessary for a definitive diagnosis. As demonstrated by this case and from previous reports, the prognosis for patients with and without surgical excision of their neoplasm remains poor to guarded.
Kurt L. Zimmerman, DVM, PhD
Department of Biomedical Sciences & Pathobiology
Virginia-Maryland Regional College of Veterinary Medicine
Blacksburg, VA 24061
Shawn P. Clark, DVM, PhD, DACVP
2400 W. Lloyd Expressway
Evansville, IN 47721
Kate Hill, BVSc(Hons), DACVIM
Veterinary Teaching Hospital
Palmerston North, New Zealand
Peter Laverty, BVSc, MACVSc, DACVS
Melbourne Veterinary Specialist Centre
70 Blackburn Road
Glen Waverley, VIC 3150, Australia
Armando Irizarry, DVM, PhD, DACVP
Eli Lilly & CO
2001 W. Main St.
Greenfield, IN 46140
Tanya LeRoith, DVM, PhD, DACVP
Department of Biomedical Sciences & Pathobiology
Virginia-Maryland Regional College of Veterinary Medicine
Blacksburg, VA 24061
Dennis DeNicola, DVM, PhD, DACVP
1 IDEXX Drive
Westbrook, ME 04092
1. Sherwin RS, Hendler R, DeFronzo R, et al. Glucose homeostasis during prolonged suppression of glucagon and insulin secretion by somatostatin. Proc Natl Acad Sci USA 1997;74:348-352.
2. Chastain MA. The glucagonoma syndrome: a review of its features and discussion of new perspective. Am J Med Sci 2001;321:306-320.
3. Bloom SR, Polak JM. Glucagonoma syndrome. Am J Med 1987;82(5B):25-36.
4. Wermers RA, Fatourechi V, Wynne AG, et al. The glucagonoma syndrome. Clinical and pathologic features in 21 patients. Medicine (Baltimore) 1996;75:53-63.
5. Allenspach K, Arnold P, Glaus T, et al. Glucagon-producing neuroendocrine tumour associated with hypoaminoacidaemia and skin lesions. J Small Anim Pract 2000;41:402-406.
6. Turek MM. Cutaneous paraneoplastic syndromes in dogs and cats: a review of the literature. Vet Dermatol 2003;14:279-296.
7. Capen C. Tumors of the endocrine gland. In: Moulton J, ed. Tumors in domestic animals. 3rd ed. Berkeley, Calif: University of California Press, 1990;616-623.
8. Cerundolo R, McEvoy F, McNeil PE, et al. Ultrasonographic detection of a pancreatic glucagon-secreting multihormonal islet cell tumour in a dachshund with metabolic epidermal necrosis. Vet Rec 1999;145:662-666.
9. Gross TL, O'Brien TD, Davies AP, et al. Glucagon-producing pancreatic endocrine tumors in two dogs with superficial necrolytic dermatitis. J Am Vet Med Assoc 1990;197:1619-1622.
10. Miller WH, Anderson WI, McCann JP. Necrolytic migratory erythema in a dog with a glucagon-secreting endocrine tumor. Vet Dermatol 1991;2:179-182.
11. Torres S, Johnson K, McKeever P, et al. Superficial necrolytic dermatitis and a pancreatic endocrine tumour in a dog. J Small Anim Pract 1997;38:246-250.
12. Hawkins KL, Summers BA, Kuhajda FP, et al. Immunocytochemistry of normal pancreatic islets and spontaneous islet cell tumors in dogs. Vet Pathol 1987;24:170-179.
13. O'Brien TD, Hayden DW, O'Leary TP, et al. Canine pancreatic endocrine tumors: immunohistochemical analysis of hormone content and amyloid. Vet Pathol 1987;24:308-314.
14. Torres SM, Caywood DD, O'Brien TD, et al. Resolution of superficial necrolytic dermatitis following excision of a glucagon-secreting pancreatic neoplasm in a dog. J Am Anim Hosp Assoc 1997;33:313-319.
15. Byrne KP. Metabolic epidermal necrosis-hepatocutaneous syndrome. Vet Clin North Am Small Anim Pract 1999;29:1337-1355.