Abstract
Pituitary dwarfism has been described in more than 20 German shepherd dogs. Some cases probably were caused by persistent cysts of Rathke's pouch. This is the first histopathological, immunohistochemical and endocrinological study.
A 13-month-old, 7-kg, dwarf purebred German shepherd bitch with alopecia and hyper pigmentation was admitted to the clinic for euthanasia. Retardation of growth was noticed when the dog was about two months old. No littermates had this condition. Two subsequent breedings from the same parents produced normal offspring.
The clinical parameters in our dog (hematology, function of liver and kidney) were normal. Grossly, the pituitary gland had small and large multiple cysts, which light microscopy showed to be exclusively within the adenohypophysis. The latter had pressure atrophy, and immunohistochemically showed only remnants of the hormone-producing cells (growth hormone—GH; prolactin—PRL; thyrotropin—TSH; luteinizing hormone—LH; adrenocorticotrophin—ACTH/MSH). The thyroid was relatively small, and histologically showed focally resting follicles without lumen.
Endocrinological studies showed a surprisingly high value for serum growth hormone (cGH 4.1 ng/ml; normal range 1.8–3.8 ng/ml as determined by a specific homologous radioimmunoassay) and a pathologically low serum somatomedin (SM 0.132; normal value more than 0.50 unit/ml, determined by 35S incorporation in piglet rib cartilage). Hypothyroidism was verified by a low T4 binding value (T4 0.9 μg/100 ml; normal 4.1 ± 0.9 μg/100 ml) and a low thyroid binding index (TBI 0.54; normal 0.61 ± 0.05). While ACTH was lowered (ACTH <10 pg/ml; normal 74–210 pg/ml), cortisol was normal (0.81 μg/100 ml; normal 0.5–2.5 μg/100 ml).
Pituitary dwarfism in the 13-month-old bitch can be ascribed to the persistence of one end of the ductus craniopharyngeus. Rathke's pouch. Pressure atrophy of the adenohypophysis led to the loss of most of the hormone-producing tissue. An increase in growth hormone with lowered somatomedin raises questions. We have no conclusive explanation for this, due to the present lack of knowledge of how growth is regulated. High growth hormone and low somatomedin values are found in Laron's syndrome in infants. The literature indicates that pituitary dwarfism in German shepherd dogs may be a hereditary autosomal recessive trait.