Acromegaly

Question 1

What causes acromegaly?

Answer 1

(Hypersomatotropism)
Excessive secretion of growth hormone and effects on target organs
Anabolic effects
Also d/t intermediary effects of IGF1, released by the liver in response to GH

Cats = pituitary adenoma, Dogs = from mammary tissue

Question 2

What is the classic signalment of an acromegalic?

Answer 2

older male cat with uncontrollable DM

Question 3

Outline the pathophysiology of Acromegaly

Answer 3

Decrease in insulin receptors and increase in insulin receptor binding
Post receptor antagonism - GH antagonises the peripheral action of insulin
B cell hyperplasia
AM leads to DM d/t insulin secretory capacity being exceeded

Question 4

Outline the anabolic effects of GH

Answer 4

Increase in lean body mass
GH promotes ketogenesis
Somatomedins increase glucose uptake by adipocytes and inhibit lipolysis
Increased IGF1 = growth and enlargement of all organs in the body

Question 5

Outline the effects of IGF1 on different organs

Answer 5

Heart - increased collagen content in cardiac muscle - hypertrophy of individual cells - HCM

Acromegalic arthropathy - IGF1 induces cartilage hyperplasia and hypertrophy

Skin - increased proliferation of fibroblasts/ collagen - can look like myxoedema, get large skin folds

Question 6

What are the main clinical signs of acromegaly

Answer 6

PUPD
PP
Hepatomegaly
Cardiomegaly
Insulin resistance

Question 7

What are some of the visible changes that can be seen in acromegalic cats?

Answer 7

Increased weight when DM uncontrolled
Enlargement of extremities (paw/ chin/ skull)
Clubbing of feet
Increased interdental spaces
Poss high PB
Neuro signs d/t pituitary tumour

Question 8

What may you see on clin path with an acromegalic?

Answer 8

Poss erythrocytosis
High BG
High fructosamine
High cholesterol
CKD can develop later in course in 50% cats

Question 9

What can you see on rads?

Answer 9

Heart - increased chamber size/ cardiomegaly/ signs of CHF
Hepatosplenomegaly/ renomegaly
Periosteal reactions, osteophytosis, joint space alterations, hyperostosis of skull and other bones, signs of degenerative arthropathy, hyperostosis of skul and other bones

Question 10

What are the ddx for an acromegalic?

Answer 10

Drugs
Poor administration
HAC
hyperthyroidism
Uraemia
Obestiy
Infection
Anti insulin Abs
Glucagonoma/ phaeochromocytoma

Question 11

What are the main ways of ix?

Answer 11

IGF1
Ix for DM
GH assays - not commercially available, possibly good sens and spec
Pituitary imaging (CT/ MRI, 10% wont have visible lesion)

Question 12

Outline IGF1 testing

Answer 12

Normally v high in AM cats
high does not equal definitive dx
Can be low until the cat has been tx for DM so can’t be used as a screening test
V cost effective

Question 13

What are the tx options?

Answer 13

Radiotherapy - most widely done, multiple fractions over 4 weeks, minimal tox although high cost and limited availability. Can cause acute onset neurosigns d/t swelling, low BG, poss long term damage to nervois tissue

Sx - transphenoidal hypophysectomy, v rare

Medical tx for insulin - must be on appropriate diet, sometimes need short acting insulin at meal times

Question 14

What is the prognosis for acromegaly

Answer 14

Short term - good

Long term poor - oft die of HCM/ renal dz or neuro signs