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
hyperpigmentation 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 micrograms/100 ml; normal 4.1 +/- 0.9 micrograms/100 ml) and a low thyroid binding index (TBI 0.54; normal 0.61 +/- 0.05). While
ACTH was lowered (
ACTH less than 10 pg/ml; normal 74-210 pg/ml),
cortisol was normal (0.81 micrograms/100 ml; normal 0.5-2.5 micrograms/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.