Pituitary disease in small animals

Question 1

Hypersomatotrophism (‘Acromegaly’) - Pathogenesis

Answer 1

incr pituitary gland activity
autonomus production of GH - elevated levels of IGF1 and its binding proteins - induces tissue proliferation & hyperplasia
cats - pituitary tumour
dogs - no reported case of a functional pituitary tumour causing hypersomotrophism - all cases d/t incr GH secretion from mammary tissue
juveniles - incr length of long bones, once growth plates have fused changes confined to soft tissue and flat bones
GH is an insulin antagonist - glucose intolerance + many have diabetes mellitus - difficult to control due to insulin resistance

Question 2

Hypersomatotrophism - Hx + clinical signs

Answer 2

PU/PD & polyphagic with weight gain
‘thick-set’ facial features
incr interdental spaces
some signs d/t poorly controlled diabetes mellitus -hepatomegaly & cataracts (dogs)

Question 3

Hypersomatotrophism - diagnostic aids

Answer 3

serum GH estimation
serum IGF1 estimation - useful for dogs, not cats
serum progesterone levels + abdominal ultrasound in dogs
CAT or MRI scan in cats

Question 4

Hypersomatotrophism - therapy

Answer 4

dogs - remove progesterone influence

cats - dopamine agonists, local irradiation, somatostatin analogues

Question 5

Hyposomatotrophism (‘Dwarfism’) - pathogenesis

Answer 5

decr pituitary gland activity
congenital malformation of the pituitary adenohypohysis or in trophic hormone producing cell lines
decr secretion of GH + TSH.
sometimes decr gonadotrophin secretion
ACTH production is usually adequate and posterior pituitary structure & function remain normal

Question 6

Hyposomatotrophism - Hx + clinical signs

Answer 6

small stature and immature hair coat
changes evident at 6-8weeks - earlier with concurrent hypothyroidism
non chondrodystrophic dwarfism, generally less than 50% normal size
persistent oestrus
normal life expectancy

Question 7

Hyposomatotrophism - diagnostic aids

Answer 7

serum GH estimation - relatively unavailable
serum IGF1 estimation – possibly valuable in dogs
delayed growth plate closure

Question 8

Hyposomatotrophism - therapy

Answer 8

none required

consider progestin therapy

Question 9

Diabetes insipidus - pathogenesis

Answer 9

decr vasopressin secretion from the posterior pituitary
Occasionally secondary to an expanding mass lesion or congenital abnormality - most commonly idiopathic
decr ADH = collecting tubules impermeable to water - urine is persistently & unremmitingly hyposthenuric

Question 10

Diabetes insipidus - Hx + clinical signs

Answer 10

marked and unremitting PU/PD

otherwise unremarkable both on history and PE

Question 11

Diabetes insipidus - diagnostic aids

Answer 11

urine sg < 1.008
biochemical screen to preclude other causes of PU/PD
an inability to concentrate urine with confirmed dehydration; documented by a water deprivation test
marked incr in urine sg after subcutaneous administration of desmopressin
low dose dexamethasone suppresion test to preclude hyperadrenocorticism

Question 12

Diabetes insipidus - therapy

Answer 12

desmopressin nasal spray administered onto the ocular conjunctiva every 12 – 24 hours
injectable desmopressin given subcutaneously every 12 –24 hours
adjust dose on the basis of water consumption, urine conc and body weight