Unusual Endocrine Disorders in Small Animals Flashcards
Insulinomas are tumors of the _____
Beta cells of the pancreas
- Which secrete excess insulin
Most insulinomas are ________
Malignant, and most will have already spread to the local lymph nodes, liver or omentum
Note: in humans, insulinoma is usually a benign tumor
How can an insulinoma be definitively diagnosed?
1) Measure fructosamine levels: if low it is suggestive of an insulinoma
2) Fast the animal, pushing them into a hypoglycemic state, then measure insulin levels: if insulin remains high, you can confirm an insulinoma
3) Abdominal ultrasound to confirm a tumor
You notice a dog is hypoglycemic, what are the potential DDx for hypoglycemia?
- Insulinoma
- Paraneoplastic syndrome
- Hepatic disease
- Sepsis
- Hypoadrenocorticism
- Toxicosis: ethylene glycol or xylitol
less commonly:
- Hunting dog hypoglycemia
- Glycogen storage disease
- Neonatal/ toy dog breeds: are often hypoglycemic in any diseased state
- Drug therapy: propranolol, salicylate and insulin overdose
- Poor sample handling: delayed separation or erythrocytosis
You fast a dog who you suspect has an insulinoma, you then measure insulin levels which are 29+ uIU/mL, what is your diagnosis?
This is absolute hyperinsulinemia, insulinoma can be diagnosed
You fast a dog who you suspect has an insulinoma, you then measure insulin levels which are between 15-29 uIU/mL, what is your diagnosis?
This is relative hyperinsulinemia, insulinoma can be diagnosed
You fast a dog who you suspect has an insulinoma, you then measure insulin levels which are between 12-15 uIU/mL, what is your diagnosis?
This is equivocal hyperinsulinemia, insulinoma is possible but further investigation should be done
You fast a dog who you suspect has an insulinoma, you then measure insulin levels which are <12 uIU/mL, what is your diagnosis?
This is the appropriate level of insulin in a hypoglycemic state, therefore this is not an insulinoma
How can an insulinoma be treated/ managed?
- Diet: frequent feeding of diabetic diets (high fibre, high protein)
- Prenisolone: 0.2-0.5 mg/kg/day (below anti-inflammatory levels)
- Diazoxide: 10-60 mg/kg/day but very expensive
- Surgical removal of the tumor is the treatment of choice in dogs
- Streptozocin treatment: chemotherapeutic
- Toceranib: chemotherapeutic
Why is Xylitol toxic to dogs?
While xylitol is an artificial sweetener, without calories. In humans it will NOT trigger the release of insulin, however, in dogs, it will trigger the release of insulin and therefore can lead to a hypoglycemic crisis, neurological deficit and death
How can hypoglycemia be managed in a patient (regardless of cause)?
- Provide food if the animal is eating, force feed honey or Dextrose gels.
Neonatal animals may require a stomach tube - IV Dextrose
First: dilute 50% Dextrose with saline in a 1:1 ratio, creating a 25% solution
Administer at a rate of 2mL/kg slowly, regularly checking BG
We may then switch to a 2.5-5% dextrose solution by mixing 100mL of 50% dextrose into a 1L bag of fluids, provide to effect, measure BG every hour until stable then administer every 4-6 hours
Describe Pituitary dwarfism in dogs, and why it happens
Pituitary dwarfism occurs most frequently in German Shepherds but has been reported in other breeds such as the Spitz, Miniature Pinscher, and Karelian Bear Dog. It is inherited and results in failure of the pars distalis of the pituitary to develop during gestation. This leads to a deficiency of all the pituitary trophic hormones (GH, TSH, Prolactin, FSH/LH, however not in ACTH)
note: ACTH producing cells have already differentiated and therefore they are unaffected, this means cortisol levels will not be altered
How can Pituitary Dwarfism be diagnosed?
- Clinical signs are usually enough as it is quite obvious
- Measure IGF-1 concentrations: low value = pituitary dwarfism
- Genetic test (identifies carriers)
How can Pituitary Dwarfism be treated?
- Growth Hormone (human or porcine available): this has side effects though, it is potentially antigenic and the dog may develop antibodies against the GH
GH is also insulin-antagonistic, and there is a high chance the dog will develop DM
GH supplementation will NOT increase the size of the dog because the growth plates have closed already
–> NOT AVAILABLE IN IRELAND - Progestagens: these will stimulate mammary GH production and is known to improve coat condition, however it can induce DM. Also, females need to be spayed because long term use of progestagens can be problematic
- Thyroid hormone supplementation
What is the prognosis of Pituitary Dwarfism in dogs?
Most only live to 2-5 years or are euthanized due to the lack of renal development and subsequent renal failure, or due to the progression of DM (from treatment therapies)
Can cats develop hyperadrenocorticism?
Yes its possible, same etiology as dogs- usually older cats that develop a pituitary tumor or functional adrenal tumor
However, it is very rare and <150 cases have been documented
What are the clinical signs associated with hyperadrenocorticism in cats?
- Diabetic: almost all cats are diabetic
- PU/PD
- Weight loss
- Polyphagia
- Severe skin changes, alopecia and fragile skin due to the excess secretion of glucocorticoids
What are the key differences in canine and feline hyperadrenocorticism?
- Almost all cats are diabetic, meanwhile, only 10% of dogs are diabetic
- Cats develop extremely fragile skin, but this is not seen in dogs
- Cats urine SG is rarely low
- Liver enzyme elevations are not as pronounced in cats as it is in dogs. This is because there is no steroid-induced ALP isoenzyme in cats like there is in dogs. Also, the half-life of ALP in cats is very short compared to the weeks-to-months half-life in dogs
How can feline hyperadrenocorticism be diagnosed?
Same as dogs: ACTH stim test and Low Dose Dexamethasone Suppression Test
However, we use a higher dose of Dex in cats than we do in dogs
We may also combine the two tests into one to hurry up the diagnosis in cats
e. g.
1) Measure basal cortisol level
2) Inject 0.1 mg/kg Dex IV
3) Cortisol measurement 3-4 hours later
4) Inject 125 ug of ACTH IV
5) Measure cortisol 1 hour later
6) Looking for lack of suppression after Dex administration, and excess stimulation after ACTH administration
- Abdominal U/S can also help measure the adrenal glands and depict if both or one adrenal gland is affected
What is the treatment of hyperadrenocorticism in cats?
Same as dogs
- Bilateral adrenalectomy: but must then be maintained as a hypoadrenocorticism patient
- Mitotane: slow and unpredictable response
- Trilostane: variable response but most useful than Mitotane
Why does Acromegaly occur in dogs, compared to why it occurs in cats?
Cats: acromegaly occurs due to a pituitary tumor which secretes excess GH
Males predisposed
Dogs: Excess GH is induced by endogenous progesterone or exogenous progestagens
Females predisposed
What are the clinical signs associated with Acromegaly in cats compared to dogs?
Cats: clinical signs associated with diabetes as almost all are diabetic, prognathism, more masculine appearance, large paws, hypertrophic cardiomyopathy, arthritis (due to cartilage changes)
Dogs: prognathism, widened interdental spaces, respiratory stridor (due to cartilage changes), and arent always diabetic
How can Acromegaly be diagnosed?
- Measure IGF-1 concentrations: a value 1000 ng/mL or above is suspicious of acromegaly
- Advanced diagnostic imaging: CT scan
What is the treatment difference between dogs and cats with Acromegaly?
Dogs: remove the source of progesterone/ progestagens = Spay or can do a mammary strip but this is far more invasive
Cats: treat the diabetes, radiotherapy or hypophysectomy
Hyperaldosteronism (aka Conn’s Syndrome) is mainly a disease of ______
- Cats
Only 1 has been reported in dogs in the literature, could be under recognized
What is the underlying cause of Hyperaldosteronism (aka Conn’s Syndrome) in cats?
- usually an adrenal adenoma
- less commonly an adrenal carcinoma
Either way, excess aldosterone is produced and secreted
What are the clinical signs associated with Hyperaldosteronism (aka Conn’s Syndrome) in the cat?
Signs associated with hypokalemia: weakness, lethargy, ventral flexion of the head, prolonged Q-T interval leading to ventricular fibrillation
Signs associated with hypertension: retinal degeneration or detachment, blindness, cardiac or neurological issues
How can Hyperaldosteronism (aka Conn’s Syndrome) be diagnosed?
There are many other and more frequently seen causes of hypokalemia and hypertension
Diagnosis of Hyperaldosteronism is usually based on the exclusion of other diseases first since they are far more common
- Ultrasound can aid in finding a mass on the adrenal glands
What is the treatment for Hyperaldosteronism (aka Conn’s Syndrome)?
- Potassium supplement: IV or orally
- Aldosterone antagonist: Spironolactone
- Hypertensive medication
- Surgical removal of adrenal tumor
What is the most common form of Feline Hypothyroidism?
- iatrogenic: either due to radioactive thyroid therapy or a thyroidectomy
However adult-onset primary hypothyroidism and congenital causes have been documented
How is hypothyroidism diagnosed in cats?
- Measurement of a low T4, but elevated TSH
How is hypothyroidism treated in cats?
- L-thyroxine supplementation (same as it is in dogs)
What is the most common underlying cause of canine hyperthyroidism?
- Thyroid carcinoma: usually locally aggressive and metastatic
Unless food-induced due to low iodine
What is the treatment of choice for canine hyperthyroidism caused by a thyroid carcinoma?
- Surgical removal +/- chemotherapy
What is Alopecia X and what breeds are predisposed?
Alopecia X is a syndrome in dogs characterized by hair cycle arrest, endocrine alopecia (non-pruritic, symmetric along the trunk, sparing of the head and legs), and hyperpigmentation
Predisposed dogs: Poodles, Pomeranian, chow, samoyed, and keeshond
Alopecia X is somewhat of an umbrella term that encompasses previously named syndromes such as growth hormone (GH)–responsive dermatosis, castration-responsive dermatosis, biopsy-responsive dermatosis, and congenital adrenal hyperplasia–like syndrome
How is Alopecia X usually diagnosed?
- Clinical signs, and ruling out other endocrine causes of alopecia listed below:
- Hypothyroidism
- Hyperadrenocorticism
- Seasonal alopecia: common in Boxers
- Sertoli cell tumor
- Hypo/ Hyperestrogenism
- Telogen effluvium: temporary hair loss after a stressful event, trauma, or shock
- Follicular dysplasia
- Pattern baldness
- Post clipping alopecia
note: a skin biopsy will point towards an endocrine alopecia, but pathologists will not be able to differentiate Alopecia X specifically. However, the regrowth of hair around the biopsy site is indicative of Alopecia X
What is the treatment for Alopecia X?
- Melatonin: the least innocuous and nonspecific treatment option. Melatonin controls the circadian and seasonal reproductive and hair growth cycles
- Spay/ Castration
- Low dose Mitotane or Trilostane
- Wear a winter coat: this is an aesthetic disease, it has no systemic effects and no detriment on survival
