Congenital Panhypopituitarism

• Rare in animals, reported in German Shepherd Dogs
• Deficiency of growth hormone
• Proportionate dwarfism
• Growth plates remain open for up to 4 years
• Disorganised proliferating chondrocytes

Also known as Pituitary Dwarfism, Congenital Panhypopituitarism is defined by failure of differentiation of oesophageal ectoderm from which the pituitary is derived. The pituitary is replaced by a cystic dilatation of Rathke's Cleft which replaces normal tissue with multilocular cysts- lined with non-secretory cuboidal epithelium.

Cystic Rathke's Pouch. Courtesy of A. Jefferies

Incidence:

• Seen in German Shepherd Dog. Inherited as a simple autosomal recessive trait in affected dogs.
• Congenital hypoplasia of the pituitary in the cat has also been reported.

Clinical signs:

Variable with degree of involvement of the pituitary. Most obvious signs are due to the lack of GH during the growing phase of the puppy's life:

• Pups appear normal at birth as the placenta supplies the foetus' need for GH.
• Retarded growth and proportionate dwarfism.
• Delayed growth plate closure; long bone physes normally close at 7-12 months but those of a pituitary dwarf will remain open until 3-4 years.
• Delayed dental eruption.
• Prognathism; undershot lower jaw as GH needed for mandible length.
• Pups are quieter, more nervous and perhaps slower to learn.
• Retention of puppy coat; wooly. Adult coat does not develop and a bilaterally symmetric, non-pruritic alopecia occurs over areas of friction E.g. neck and trunk.
• Hyperpigmentation with comedomes.
• Reproductive signs E.g. failure to cycle, testicular atrophy.

May also see signs of

• Secondary hypothyroidism
• Secondary hypoadrenocorticism

Diagnosis:

• Presumptive diagnosis based on signalment and clinical signs.
• Radiography to detect growth plate closure.
• GH stimulation test; Use alpha-2 agonist E.g. Xylazine which inhibit somatostatin and so induce GH production and release. Normal dogs will have 2-4X increased GH after 20 mins while a pituitary dwarf will show little change in GH upon stimulation.
• Somatomedin Assay; Also called insulin-like growth factors. GH mediates its effects by stimulating the production of IGFs which can be more easily measured. Low levels will be found in pituitary dwarfs.
• May also need to consider TSH and ACTH stimulation tests.

Treatment:

Need to treat early or will remain dwarfs.

• Sub-cut bovine/human GH can induce the growth of an adult haircoat.
  Nb. GH is diabetogenic so overdose will induce Diabetes Mellitus.
• Progestagens may induce GH production from the mammary gland.
• May need to replace thyroid hormones and/or glucocorticoids.