Veterinary Endocrine and Metabolic-Small Animal

Endocrine and Metabolic Disorders in Small Animals – Comprehensive Study Notes

  • Adrenal gland anatomy and hormone production

    • Adrenal cortex vs medulla
    • Cortex: produces glucocorticoids (e.g., cortisol), mineralocorticoids (e.g., aldosterone), and adrogenic hormones
    • Medulla: produces epinephrine and norepinephrine
    • Functional take-home: know where each class of hormones is produced and their primary roles

  • Glucocorticoids (cortisol) – key points

    • Role in medicine: broadly used as anti-inflammatory steroids at low doses; can promote gluconeogenesis (glucose production) at baseline physiologic levels
    • Immunomodulation: at higher doses, suppress the immune system
    • Dosing caution: dosing determines whether anti-inflammatory effects or immunosuppression dominate
    • Not essential for life: glucocorticoids are not required for life, but mineralocorticoids are essential
    • Clinical implication: iatrogenic Cushing’s syndrome results from excess glucocorticoids

  • Mineralocorticoids

    • Primary example: aldosterone
    • Function: regulate electrolytes, fluid balance
    • Essential for life; deficiency leads to Addison’s disease (hypoadrenocorticism)

  • Addison’s disease (hypoadrenocorticism) vs Cushing’s disease (hyperadrenocorticism)

    • Addison’s (hypoadrenocorticism)
    • Pathophysiology: cortex atrophy → decreased glucocorticoids and mineralocorticoids
    • Disease rarity: rare, often underdiagnosed; Addisonian crisis is the most common way diagnosed
    • Typical clinical signs: vague, primarily gastrointestinal (vomiting, diarrhea), lethargy, anorexia, weight loss; signs can wax and wane due to fluctuating aldosterone production
    • Signal phrases: important to consider in differential for GI signs in middle-aged, female dogs
    • Diagnostics: CBC not pathognomonic; chemistry may show electrolyte abnormalities (Na+ and K+ imbalance); Na:K ratio is a key clue
    • Definitive test: ACTH stimulation test
      • Procedure: draw baseline cortisol, administer ACTH, draw cortisol at 30 minutes post-injection
      • Interpretation: Addison’s → low cortisol that fails to rise after ACTH; normal animals show cortisol rise
    • Acute management (Addisonian crisis): saline bolus IV, dexamethasone (glucocorticoid) or other steroid, supportive care (oxygen if cyanotic, warming if hypothermic)
    • Chronic management: lifelong therapy
      • Glucocorticoid replacement (daily)
      • Mineralocorticoid replacement (e.g., long-acting injectable; monthly) – note: “Florineph” in notes is a reference to a long-acting mineralocorticoid; in small animals, DOCP (desoxycorticosterone pivalate) is commonly used; practice notes suggest this monthly injection approach though some products/regions may differ
      • Prognosis: generally good with proper replacement therapy
    • Cushing’s disease (hyperadrenocorticism)
    • Pathophysiology: overproduction of cortisol; common in dogs
    • Common clinical signs related to steroid excess or metabolic effects
      • Abdominal distention (pot-bellied appearance)
      • Polyuria (PU) and polydipsia (PD), polyphagia, weight gain, panting
      • Edema and bilateral truncal alopecia
      • Possible calcinosis cutis in long-standing cases
      • Possible reproductive effects in intact animals
    • Diagnostic hints
      • Liver enzymes often elevated (ALP and ALT)
      • Possible hyperglycemia; decreased BUN
      • Hypercholesterolemia can be present (not explicitly stated but common in practice)
      • Low-dose dexamethasone suppression test (LDDST) as historical or common diagnostic approach; MRI/CT/adrenal imaging and ACTH stim are also used depending on the case
    • Diagnostic test of choice (per notes): low-dose dexamethasone suppression test (LDDST)
      • Procedure: measure baseline cortisol, inject dexamethasone, measure cortisol at 6 hours and 8 hours
      • Interpretation: suppression of cortisol at 6 hours with rebound by 8 hours is abnormal and suggests hyperadrenocorticism; suppression can persist for up to 24 hours in normal animals
    • Treatment options
      • Medical management is common; surgical adrenalectomy is an option but less common
      • Trilostane (brand examples: Trilostane/Vetoryl) is widely used; previously used mitotane (Lysodren) and related therapies
      • Some cases may require a combination of therapies; medical management is most common in primary care
      • The need for veterinary internal medicine or endocrinology referral for complex cases or surgical decisions
    • Practical notes
      • Mineralocorticoids are life-sustaining; glucocorticoids are less critical but still necessary to manage cortisol excess and symptoms
      • tapering of glucocorticoids is important to avoid adverse effects and to minimize stress

  • Parathyroid glands and calcium balance

    • Anatomy and function
    • Parathyroid glands sit on or near the thyroid; regulate calcium via parathyroid hormone (PTH)
    • PTH promotes bone resorption and renal calcium reabsorption to raise serum calcium
    • Primary hyperparathyroidism
    • Cause: tumor on the parathyroid gland causing excess PTH
    • Clinical signs: often found on routine blood work; hypercalcemia, often with concurrent hypophosphatemia
    • Diagnostic pointers: hypercalcemia usually > 12extmg/dL12 ext{ mg/dL}; phosphorus often low; direct PTH measurement is expensive; diagnosis often inferred from response to treatment or imaging
    • Other causes of hypercalcemia to consider: thyroid disease or other bone disease
    • Hypercalcemia of malignancy: anal gland adenocarcinomas can cause significant hypercalcemia
      • Diagnostic approach if hypercalcemia detected: consider parathyroid vs malignancy; assess for anal gland tumor when calcium is elevated
    • Hyperparathyroidism treatment considerations
    • Surgical removal of the tumor is possible when a tumor is identified
    • Debulking and partial resection may reduce PTH secretion
    • Post-treatment management may require vitamin D and calcium supplementation rather than calcium binders alone
    • Ultrasound or imaging may help locate the parathyroid gland tumor; refer to internal medicine for surgical planning when needed
    • Hypoparathyroidism and hypocalcemia
    • Causes: reduced PTH leading to low calcium; chronic hypocalcemia may follow acidosis or pancreatitis; eclampsia is a post-partum risk in nursing mothers
    • Clinical signs: neurological signs (tetany, seizures), muscle tremors, facial pruritus; neuromuscular irritability is common
    • Diagnosis: serum calcium concentration; no single pathognomonic test; treatment guided by calcium levels
    • Hypocalcemia management: IV calcium gluconate (10% solution) slowly via vein with close EKG monitoring; may require oral supplementation depending on cause (e.g., ongoing hypoparathyroidism)
    • Eclampsia management: ensure adequate dietary calcium; in some cases, puppy/milk production demands are met with dietary adjustments rather than long-term supplementation
    • Pancreatitis and calcium interactions
    • Pancreatitis can cause or influence calcium abnormalities; lipase testing may be indicated
    • Clinical signs: vomiting, abdominal pain, anorexia; abdominal palpation pain can be present; consider pancreatitis in differential for vomiting

  • Calcium and nutrition counseling

    • Pregnancy and lactation: hypocalcemia risk rises around 2–4 weeks post-whelping; high-calcium nutrition around this time helps mitigate risk
    • Nutritional balancing resources
    • Balance.it is a veterinary nutritionist–designed site to help balance home-cooked diets; can prompt supplementation if meals are deficient in calcium or excessive in phosphorus

  • Diabetes mellitus – overview

    • Disease basics
    • Pancreas and insulin: insulin produced by pancreatic beta cells; without insulin, glucose remains in the bloodstream
    • Can lead to diabetic ketoacidosis (DKA) if not controlled
    • Differences between species
    • Dogs: always type 1 diabetes (insulin-dependent for life)
    • Cats: about half insulin-dependent; half may go into remission and become non-insulin-dependent over time
    • Insulin types and dependence: cats may respond to non-insulin options (e.g., glipizide) in some cases; dogs typically require lifelong insulin
    • Insulinomas: insulin-secreting tumors; rare in small animals, common in ferrets; poor prognosis in small animals when present
    • Clinical signs
    • PU/PD is the most common presentation in both dogs and cats
    • Weight loss with preserved or severe appetite in some cases; cats may appear weight stable or overweight before losing weight
    • Cataracts in diabetics; rapid development of cataracts in dogs and cats can lead to sudden vision loss in cats in particular
    • In diabetic cats, plantigrade stance may be observed
    • Diabetic ketoacidosis (DKA)
    • A severe complication presenting with dehydration, weakness, vomiting, ketotic odor, progressive decline; can be life-threatening

  • Diagnosis of diabetes mellitus

    • Core diagnostic criteria
    • Hyperglycemia: blood glucose > 200extmg/dL200 ext{ mg/dL} (in many species and settings; refer to lab reference ranges)
    • Glucosuria on urinalysis
    • Challenges and adjuncts
    • Stress hyperglycemia can confound diagnosis, especially in hospital/admission settings; more common in cats
    • Fructosamine testing reflects average glucose over ~2 weeks and helps avoid stress-related misdiagnosis
    • Continuous glucose monitoring options (e.g., Freestyle Libre) provide home or outpatient curve data and reduce the need for in-hospital glucose curves
      • Freestyle Libre: typically stays in place up to about 2 weeks; uploads data periodically to a mobile device
    • In-hospital vs home monitoring
    • If owner can collect at-home data, consider sending results to the clinic; avoid extended in-hospital glucose curves when possible

  • Diabetes mellitus treatment and management

    • Diet strategies
    • Mild cases may respond to high-fiber, complex carbohydrate diets
    • Prescription diets (e.g., RD, WD) can be effective
    • Pharmacologic therapy
    • Insulin therapy: diverse options; commonly used in dogs and cats; dosing individualized by clinician
    • Veterinary insulin products (examples mentioned: Vetsalin) and syringe compatibility must match insulin type (U-100 syringes or other specified devices)
    • Cats often start at about 1 unit of insulin twice daily; dogs typically start a lower dose than cats
    • Glipizide (oral) can be used in some cats as a glucose-lowering agent when insulin is not yet necessary or when partial response is seen; not universally effective and studies continue
    • Insulin therapy notes
    • Refrigerate insulin; avoid shaking/breaking the bottle; adhere to a strict dosing schedule (e.g., every 12 hours)
    • Many clinicians advocate feeding at least three meals per day to stabilize glucose
    • Rotate injection sites to prevent tissue discomfort or lipodystrophy
    • Avoid client-initiated dose changes without veterinary guidance; hypoglycemia is a major risk with insulin excess
    • Hypoglycemia management
    • Signs: lethargy, weakness, pale appearance, altered mentation
    • Immediate intervention: if hypoglycemic, provide quick source of glucose (e.g., Karo syrup) and contact a veterinarian
    • Owner and client education
    • Emphasize regular administration, consistent meals, and no unsupervised dose changes
    • Provide a plan for monitoring and when to seek veterinary help
    • Typical client education pathway includes a diabetic consult with hands-on training by a technician

  • Special note: Interactions and clinical pearls

    • Anal gland adenocarcinoma and hypercalcemia of malignancy
    • Anal gland adenocarcinoma can cause marked hypercalcemia; in cases of hypercalcemia, consider parathyroid or anal gland tumor as etiologies
    • Seizure management and emergency meds
    • Midazolam recommended for seizure control in clinical scenarios
    • Eclampsia and lactation-related hypocalcemia
    • Postpartum risk in nursing mothers; dietary management and monitoring are important

  • Quick reference thresholds and practical numbers (as cited in the notes)

    • Hypercalcemia threshold for primary hyperparathyroidism: typically greater than 12extmg/dL12 ext{ mg/dL} (lab reference ranges vary by lab)
    • Diabetes diagnostic criterion: fasting or random blood glucose > 200extmg/dL200 ext{ mg/dL} with glucosuria
    • Fructosamine: reflects average glucose over roughly the past two weeks
    • Freestyle Libre: continuous glucose monitor, lasts up to about two weeks
    • Insulin administration basics: cats often start around 1extunit1 ext{ unit} twice daily; dogs start lower; insulin syringes labeled for use with specific insulin concentrations (e.g., U-100)

  • Connections to foundational principles

    • Endocrine feedback loops: how pituitary and hypothalamic signals regulate adrenal and parathyroid hormones
    • Electrolyte and acid-base balance interplay with adrenal and parathyroid disorders (e.g., Na+/K+ balance in Addison’s, calcium balance in parathyroid disorders)
    • Metabolic consequences of insulin deficiency and glucocorticoid excess (e.g., hyperglycemia, lipolysis, protein catabolism, cataract formation)
    • The importance of thorough differential diagnoses when presented with nonspecific signs (vomiting, lethargy, polyuria/polydipsia, abdominal distention)

  • Practical considerations for exam preparation

    • Be able to distinguish Addison’s vs Cushing’s scenarios by clinical signs, typical lab clues (Na:K ratio, ALP/ALT patterns), and confirmatory tests (ACTH stim vs LDDST)
    • Recognize the emergency management steps for endocrinopathies (Addisonian crisis, DKA) and the rationale for rapid stabilization
    • Memorize common treatment options and their relative roles (glucocorticoid and mineralocorticoid replacement; trilostane vs mitotane; insulin types and catabolic/anaerobic considerations)
    • Understand the diagnostic pathways for calcium disorders (hyperparathyroidism vs hypoparathyroidism vs pancreatitis-related calcium derangements) and their therapeutic implications
    • Be prepared to discuss client education topics, including dosing safety, home glucose monitoring options, and the importance of consistent routines for chronic diseases