Morphologic and immunocytochemical study of young dogs with diabetes mellitus associated with pancreatic islet hypoplasia.

In 11 dogs (7 males, 4 females; 10 purebred, 1 mixed breed), diagnosed as having diabetes mellitus before the age of 6 months, the pancreas was evaluated histologically; in 6, the pancreas also was examined by use of electron microscopy and/or immunocytochemical methods. Each dog was placed in 1 of 3 groups (A through C) on the basis of pancreatic histopathologic findings: Group A (n = 3)--no recognizable islets, but the pancreas in 2 dogs contained scattered endocrine cells detectable by use of immunoperoxidase staining or electron microscopy; Group B (n = 4)--no recognizable islets, but the pancreas had severe vacuolation of ducts and acini, as well as acinar atrophy; Group C (n = 4)--scant shrunken islets; 1 pancreas had reduced numbers of recognizable islets, hydropic beta-cell vacuolation attributable to glycogen deposition, and islet and nonislet endocrine cells in expected proportions. Insulitis was not observed in any pancreas, although scattered lymphocytes were seen in the pancreatic interstitial fibrous tissue of 3 dogs. Histologic pancreatic lesions in these young dogs were distinct from those of type-I (insulin-dependent) diabetes mellitus in human beings, as well as from those of diabetes mellitus in aged dogs, but were similar to those described in other young diabetic dogs. This uncommon syndrome is distinct from commonly recognized canine diabetes mellitus, on the basis of age of onset, predisposition for purebred dogs, lack of predisposing endocrinopathies or obesity, and pancreatic histologic features. The cause(s) is unknown, but is related to pancreatic endocrine hypoplasia and not to insulitis or to exocrine pancreatic inflammation. The term pancreatic islet hypoplasia is chosen as best describing this disorder.