Cushings SA

Presenting signs

·    PUPD

·    Abdominal enlargement, pot belly

·    Polphagia

·    Skin changes – bilateral, symmetrical alopecia, thin skin, reduced elasticity, scale/comedones, slow healing, calinosi cutis, non-pruritic

·    Hepatomegaly

·    Muscle wasting/weakness, lethargy, exercise intolerance

·    Reproductive changes

Risk factors

·    PDH – middle-aged, small dog breeds

·    ADH – older, large dog breeds

Diagnosis

·    Need to be suspicious

·    Blood sample for H+B

o  Haematology – stress leukogram

o  Biochemistry – incr. ALKP, ALT, hyperglycaemia, hyperphosphataemia, incr. cholesterol and triglyceride

·    Imaging – abdominal radiographs (hepatomegaly, calcinosis cutis, distended bladder), thoracic radiographs (tracheal/bronchial mineralisation)

·    Urinalysis – USG <1.030, despite dehydrated status (as cortisol inhibits ADH action)

Specific tests:

·    Low dose dexamethasone suppression test

o  Method: starve overnight, measure baseline cortisol, inject dexmeth, measure cortisol at 3 and 8h

o  Normal result = reduced cortisol release from adrenal gland (cortisol <50nmol/l at 8h)

o  Positive result = reduced/absent response

o  Good sensitivity (if negative, rule out cushings), but low spec

·    ACTH stimulation test:

o  Method: starve animal overnight, test plasma cortisol at time 0, inject synthetic ACTH, collect sample 60m later and re-test

o  Normal result = pre-stim <200nmol/l, post-stim <600

o  Positive = post-stim >600

o  High specificity (if positive, defo has cushings), okay sens

o  If no increase post-stim = iatrogenic HAC

·    Urinary cortisol:creatinine ratio

o  Low ratio = rule out HAC

o  High ratio = could be HAC, but could be something else

·    To differentiate between ADH and PDH

o  Exogenous ACTH

§ PDH = tumour releasing ACTH, so ACTH will increase

§ ADH = tumour releasing cortisol, so ACTH will decrease

o  Adrenal imaging

§ PDH = symmetrical enlargement

§ ADH = one enlarged gland, one atrophied gland

Management

·    Medical management – Trisolastane

o  Prevents conversion of pregnelone ® progesterone, so less cortisol is produced

o  Can have increase in adrenal gland size as consequence

·    Surgical treatment

o  Adrenalectomy for ADH

o  Hypophysectomy for PDH

o  But requires life-long hormone replacement therapy

·    Prognosis – better for PDH