Equine Endocrine and Metabolic Diseases Flashcards
Adrenal, Thyroid and Parathyroid Diseases
What are the 3 main Adrenal diseases of horses?
1) Adrenal Insufficiency
2) Pheochromocytoma
3) Anhidrosis
What are the 2 main Thyroid gland diseases of horses?
- Neonatal hypothyroidism
- Thyroid tumors
What are the 2 main Parathyroid gland diseases of horses?
- Hyperparathyroidism
- Pseudohyperparathyroidism
What are the 2 main Pancreatic diseases of the horse?
- Diabetes mellitus: rare
- Hypoglycemia: rare, but may occur due to pancreatic tumor
What are the causes of Adrenal Insufficiency in the horse?
Adrenal glands are known as the ‘shock’ organs in the horse, therefore causes include:
- Endotoxemia
- Colic
- Chronic use of corticosteroids, or at higher doses
Both of which lead to hemorrhage and necrosis of the adrenals
What are the common risk factors associated with Adrenal Insufficiency?
- Just off the track
- Intensive training
- Steroid use
- Recent colic
What are the clinical signs associated with Adrenal Insufficiency?
- Poor condition
- Poor performance
- Lethargy
- Depression
- Anorexia
- Weight loss
What are the typical findings on serum biochemistry of a horse with Adrenal Insufficiency?
- Hyponatremia
- Hypochloremia
- Hyperkalemia
- Hypoglycemia
How can Adrenal Insufficiency be diagnosed in the horse?
- ACTH gel 1 IU/kg given IM
Serum cortisol levels taken pre- and 2-4hours post administration
note: normal horse will see a 2-3x increase in cortisol conc
note: a horse with Adrenal Insufficiency will see less than this
What is the treatment for Adrenal Insufficiency in the horse?
- Rest and reduction of stress
- Long term corticosteroid administration should be weaned off
What is a Pheochromocytoma?
Functional adrenal medullary tumour, which causes an excess of catecholamine production from the adrenal medulla
- Catecholamines: Epinephrine, Norepinephrine and Dopamine
What are the clinical signs associated with Pheochromocytoma in the horse?
- Usually present similar to acute colic
- Increase HR
- Increase RR
- Dilated pupils
- Sweating
- Anxiety
- Diarrhea
- Muscle tremors
- PU/PD
How can Pheochromocytoma be diagnosed in the horse?
- Diagnostic imaging: limited access though
- Hematology and biochemistry: non-specific
Neutrophilia, lymphopenia: stress response
Hemo-concentration: splenic contraction
Hyperglycemia, uremia, hyper-kalemia
note: usually diagnosed on the table while the horse is undergoing colic surgery- since this is similar to how they present
What is the treatment of Pheochromocytoma in the horse?
Supportive Tx: address renal function with fluids
Medical Tx: not usually attempted
Surgical Tx: high risk of cardiac arrhythmias, rhabdomyolysis and excess bleeding
What is Anhidrosis?
The inability to sweat normally, which can lead to hyperthermia and heat exhaustion
A horse that came from a relatively cold climate to a warmer climate is more predisposed to _______
Anhidrosis within 1-3 months of arrival
This is thought to be due to sweat glands shrinking due to environmental stress or exercise
What are the clinical signs associated with Anhidrosis in the horse?
- Poor stamina and exercise intolerance
- Panting, distress and lethargy after exercise
- Heat overload + collapse
How can Anhidrosis be diagnosed in the horse?
- Usually clinical signs and a history of moving to a warm climate is enough
- Intradermal injection of Beta2-agonists
What is the treatment/ management for Anhidrosis in the horse?
- Move horse to a milder, less humid climate
- Compete during the winter months only
- Daily electrolyte supplementation
- Provide a cool environment: fans or AC, shade
- Body clipping
- Hosing with cool, water after exercise
What can Neonatal Hypothyroidism be caused by?
Neonatal goiter due to:
- Iodine deficiency in the diet of the mare
- Excess nitrates in the diet of the mare
- Ingestion of goitrogens by the dam: plant goitrogens will cross the equine placenta and interfere with iodine uptake in the gland
Where in the world is Neonatal Hypothyroidism most commonly reported?
Canada
What are the two presentations of a foal with Neonatal Hypothyroidism?
1) Foal is in hypo-metabolic state with low thyroid hormone concentration
2) Developmental lesions are found with normal thyroid hormone concentrations: this happened due to hormone deprivation during the critical period of development
What are the clinical signs associated with Neonatal Hypothyroidism?
- Dysmature
- In-coordiantion
- Poor suckling reflex and unable to right itself: neurological presentation due to hypomyelination
- Hypothermia and a low BMR
- Tendon contracture/ rupture
- Retarded bone development
- Undershot jaw: parrot mouth
How can Neonatal Hypothyroidism be diagnosed?
What is the prognosis of this disease?
- Clinical signs + history of mares diet
- TSH response test
- Post-mortem
Prognosis: poor to guarded- don’t often make it as athletes.
However it has been seen of foals with only a goiter as a presenting problem to ‘grow out’ of it and perform normally
Can adult horses get hypothyroidism?
Yes, but it is extremely rare and often over diagnosed
Typically what the horse (or pony) has is Equine Metabolic Syndrome
How can Adult Hypothyroidism be diagnosed in the horse/ pony?
- Low serum T3 and T4
- TSH stimulation test
note: other factors can lead to low T3 and T4 including- Bute (pain-killer), Food deprivation, illness
How can Adult Hypothyroidism be treated in the horse/ pony?
- Thyroxine (T4) 20mcg/kg SID po
Used for the Tx of EMS too
What are the two types of Hyperparathyroidism (aka Bran Disease)?
- Primary: rare
- Secondary: Nutritional, due to diets high in phosphorus or oxalates, which decrease the absorption of Ca in the GIT leading to Ca deficiency and PTH is secreted
What are the clinical signs associated with Hyperparathyroidism (aka Bran Disease)?
- Limb and Facial bone demineralization: loose teeth and a shifting intermittent lameness
- Weanlings and Yearlings will fail to reach their expected height
- Swollen facial bones, thickened jaw bones and difficulty chewing
- Ruptured tendons and increased risk of fractures
- Obstruction of nasal passages, which may cause a nice and/or a discharge
How can Hyperparathyroidism (aka Bran Disease) be diagnosed?
- Serum Ca and PO4: but are usually normal
- Urinary PO4 is typically elevated
What is the treatment and prevention of Secondary Nutritional Hyperparathyroidism (aka Bran Disease)?
- Tx: Dietary management
note: it can take up to 12 months for re-mineralization of the bone
Prevention: Calcium supplementation if pastures are high in oxalates
What are the most common causes of Diabetes Mellitus in the horse?
A rare condition in horses, but when it happens it is associated with Pancreatic destruction
- Abscesses: Strep equi or Corynebacterium
- Migrating Strongyles
What are the most common Metabolic Diseases of the Horse?
- Calcium: hyper and hypocalcemia
- Copper and Selenium deficiencies
- Hyperlipidosis/ Hyperlipemia
- Hepatic Encephalopathy
Why might Hypercalcemia be seen in a horse?
Paraneoplastic syndrome to:
- Lymphoma
- Gastric SCC
- Mesothelioma
Vit D Toxicosos: eating too much Vit D, leading to increase absorption of Ca and P from the GIT and reabsorption from the kidneys
How can Hypercalcemia be diagnosed in the horse?
- Serum biochemistry: elevated Ca but normal PO4
- Pathological calcification of the soft tissues
Why might Hypocalcemia be seen in the horse?
- At peak lactation, especially in draft mares: ~10 days after foaling and due to inadequate feed supplementation
- Prolonged Transportation
- Endurance-type exercise
- Severe colitis: e.g. blister beetle toxicosis
What are the clinical signs associated with Hypocalcemia?
- Tetany
- Profuse sweating
- Anxious appearance
- Tachycardia
- Cardiac arrhythmias
- Synchronous Diaphragmatic Flutter: “Thumps”- diaphragm contracts with the heart beat
What is the treatment for Hypocalcemia?
- SLOW IV Calcium supplementation
note: must monitor the heart as you do this
Why might Copper and Selenium deficiency occur in horses?
- grazing copper and selenium deficient pastures
What are the clinical signs associated Copper deficiency
- Dull, brown hair coat
- Developmental Orthopedic Disease in foals
What are the clinical signs associated Selenium deficiency?
- Muscle disease: rhabdomyolysis or white muscle disease in foals born to Cu deficient mares
- Poor growth and poor performance
- Reproductive problems
- Immune deficiency
What is another name for Selenium toxicity, and why does it occur?
Selenium toxicity = Alkali disease
- When horses ingest too much Selenium in the diet
What are the clinical signs of Alkali disease in horses?
- Fatigue
- Loss of mane and tail hairs
- Cracking of hoof and coronary band: sloughing of hooves
note: this is a life-threatning disease
What is the difference between Hyperlipidemia and Hyperlipemia in the horse?
Hyperlipidemia: mild condition, clear serum, no hepatic dysfunction
Hyperlipemia: severe condition, with fat accumulation in the liver
What are the predisposing risk factors to Hyperlipemia in horses, donkeys and ponies?
- Obesity!
- Certain equid breeds: miniature horses, pony breeds, donkeys- they are all relatively insulin resistant already, which worsens the disease
- Negative Energy Balance:
Malnutrition, starvation, anorexia or inappetance
Stress (transport, weaning, or disease)
Advanced pregnancy
Enforced feed restriction
Lactation
Pituitary pars intermedia dysfunction (PPID)
What are the clinical signs associated with Hyperlipemia?
- Depression, weakness, in-coordination, anorexia, decreased gut motility
All of which can mask the underlying disease process that is more commonly the cause for the hyperlipemia in horses
How can Hyperlipemia be diagnosed in horses?
- Serum: may be white or yellow and opaque
- Biochem: Increased hepatic enzymes, bile acids and bilirubin
Increased TGIs and FFAs
Azotemia
Metabolic acidosis can develop in late stage
What is the treatment for Hyperlipemia in horses?
- Treat the primary disease
- Nutrition: IV glucose to correct NEB +/- insulin
- Fluid therapy: correct electrolyte and acid-base imbalance
What is Hepatoencephalopathy?
Considered to be a clinical syndrome in horses, defined by an abnormal mental status, accompanied by severe hepatic insufficiency
What is the most common presentation and causes of Hepatoencephalopathy in the horse?
- Presentation: Diffuse acquired liver disease
- Causes:
Hepatic cirrhosis
Hepatic necrosis
Hepatic lipidosis –> Hyperlipemia
Cholangiohepatitis
Phytotoxic hepatitis
Mycotoxicosis
What is the most common cause of Hepatic cirrhosis in the horse?
- Ingestion of pyrrolizidine alkaloid containing plants: ragweed or ragworth
note: damage is irreversible to the liver
How can liver cirrhosis be diagnosed in the horse?
- Liver biopsy + histopathology: presence of megalocytes, portal fibrosis, biliary hyperplasia, necrosis
What are the clinical signs associated with liver cirrhosis in horses?
1) Bizarre behaviour: depression, lethargy, excessive yawning, agitation, head pressing, ataxia, compulsive walking, circling, blindness, collapse and coma
2) Laryngeal dysfunction
3) Gastric Impaction: due to vagal nerve dysfunction
What are the clinical signs associated with Hepatoencephalopathy in the horse?
- Depression
- Anorexia
- Weight Loss
- Jaundice
- Photosensitization
- Intravascular hemolysis
- Pyrexia
How can Hepatoencephalopathy be diagnosed in the horse?
- Presence of encephalopathy
- Evidence of impaired liver function: elevated serum bile acids and liver enzymes
- U/S
- Biopsy + Histopathology
- Hyperammonemia
What is the Treatment and Prognosis of Hepatoencephalopathy in the horse?
Supportive:
- I/V dextrose + electrolytes
- Monitor and correct acid-base balance
Dietary:
- Low-protein diet with a readily digestible CHO, high in branched-chain amino acids
Prognosis: poor to guarded
