Endocrinology - ADH and Calcium Flashcards
What is polyuria?
Increased urine production - 50 ml/kg/day
What is the normal urine production of a small animal?
20-45 ml/kg/day
What is polydipsia?
Increased thirst - 100 ml/kg/day
What is the normal water intake of a small animals?
20-70 ml/kg/day
True or false: The vast majority of animals are polydipsic first.
false - they are polyuric first
How does polyuria lead to polydipsia?
Polyuria leads to volume depletion which leads to polydipsia to prevent dehydration
True or False: Water restriction is not the answer to treat PU/PD.
TRUE
What are the major differential diagnoses for PU/PD?
Osmotic diuresis, diabetes insipidus, renal medullary solute washout, drug-induced, and primary polydipsia
What is osmotic diuresis?
It is when there is an increase in urine solutes resulting in water pulled into the tubule and thus increased water loss through the urine
What are some disease processes that can cause osmotic diuresis?
Diabetes mellitus/DKA, Fanconi syndrome or primary renal glucosuria, CKD/AKI, and post-obstructive diuresis
What is diabetes insipidus?
A disorder characterized by the production of a large amount of dilute urine that occurs when water is not able to be reabsorbed from the renal tubule (action of ADH)
What are the two manifestations of diabetes insipidus?
central and nephrogenic
What is central diabetes insipidus also known as?
primary pituitary DI
What is central diabetes insipidus caused by?
A lack of ADH production - there is some issue with the pituitary gland
What is nephrogenic diabetes insipidus?
There is partial or complete lack of renal response to ADH
What are the two forms of nephrogenic diabetes insipidus?
Primary and secondary/acquired
What is primary nephrogenic diabetes insipidus?
Congenital lack of ADH receptors or lack of response to ADH- it has not been described in small animals
What can cause acquired NDI?
bacterual endotoxins, hypercalcemia, hyperadrenocorticism, hypokalemia, and others
What is renal medullary solute washout?
The loss of renal medullary solutes due to an impaired ability of the nephron to concentrate urine
What are the potential causes of renal medullary solute washout?
Hepatic disease, chronic diuretic use, and many other causes of PU/PD
What drugs are the ‘common offenders’ of causing PU/PD?
Anticonvulsants, glucocorticoids, and diuretics
What is primary polydipsia?
It is polydipsia that cannot be explained as a compensatory response to excessive whater loss
What is psychogenic polydipsia?
Behavioral compulsive water consumption - diagnosis of absolute exclusion
Why does polyuria develop in cases of psychogenic polydipsia?
to prevent overhydration
What is the clinical approach to PU/PD?
Get a history to verify, do a thorough PE, do a minimum database to rule out easy causes, use a UA to look for hyposthenuria or concentrated urine, and do additional diagnostics
What additional diagnostics can be done to diagnose the underlying cause of PU/PD?
UCCR, LDDST, T4, imaging, urine culture, leptospirosis testing, bile acids
What is a Desmopressin (DDAVP) trial?
It is a synthetic ADH analog that is used to tread CDI - if given and there is a positive response it is suggestive of CDI
What is a water deprivation test used for?
To determine if the patient has the ability to concentrate urine
What is the water deprivation test used to differentiate between?
Primary/psychogenic polydipsia and diabetes insipidus
When should the water deprivation test only be performed?
If all other causes of PU/PD have been ruled out
What is the biologically active form of calcium?
ionized calcium
What does the maintenance of normal calcium depend on the interaction of?
parathyroid hormone, vitamin D, and Calcitonin
What is PTH secreted by?
chief cells of the parathyroid gland
What does PTH do in the bone?
Increase calcium mobilization
What does PTH do in the kidney?
Increases renal tubular calcium reabsorption, increase vitamin D conversion to the active form, and increases phosphorus excretion
What is the net effect of PTH action?
Increase Ca and decrease P
What does vitamin D do in the intestine?
Increaes phosphorus absorption and increases calcium absorption
What is the net effect of Vitamin D action?
Increases calcium and phosphorus
What is calcitonin secreted by?
C cells of the thyroid gland
Where is the primary site of action of calcitonin?
the bone
What is hypercalcemia?
When blood inionized calcium levels increase - PTH falls, vitamin D conversion stops, there is decreased Ca absorption from GI tract, increased renal calcium excretion, and calcium is deposited in bones
What are the etiologies of hypercalcemia?
HARDIONS G - Hyperparathyroidism, Addison’s, Renal disease, Hypervitaminosis D, Idiopathic, Osteolysis, Neoplasia, Spurious, Granulomatous disease, and Growth
What etiologies are the highest calcium levels seen with?
Primary hyperparathyroidism, neoplasia, and vitamin D toxicity
What clinical signs are associated with hypercalcemia?
PU/PD, weakness, lethargy, exercise intolerance, and inappetance
What is the clinical approach to hypercalcemia?
Complete history, physical exam, minimum data base, imaging, lymph node aspiration, bone marrow evaluation, and PTH panel/malignancy panel/vitamin D panel
What is primary hyperparathyroidism?
Excessive secretion of PTH by autonomously functioning parathyroid gland
What is the etiology of primary hyperparathyroidism?
parathyroid adenoma
What is the signlament for primary hyperparathyroidism?
Older dogs, Keenshond is overrepresented
What clinical signs are associated with primary hyperparathyroidism?
PU/PD, can present with lower urinary tract signs, clinical signs can be subtle
What will you find on diagnostic evaluation of primary hyperparathyroidism
PE is often normal and there is an elevated or inappropriately normal PTH level in the face of high ionized calcium
How is primary hyperparathyroidism treated?
Surgery, percutaneous ablation, and monitor/treat for hypocalcemia following definitive therapy
What causes hypercalcemia of malignancy in dogs?
Lymphoma, anal sac adenocarcinoma, and multiple myeloma
What causes hypercalcemia of malignancy in cats?
lymphoma and squamous cell carcinoma
What is hypercalcemia of malignancy often mediated by?
parathyroid hormone
What causes vitamin D toxicosis?
Cholecalciferol rodenticides, psoriasis medications, some plants, and iatrogenic
What are the clinical effects of vitamin D toxicosis?
Severe hypercalcemia and severe hyperphosphatemia
How is vitamin D toxicosis diagnosed?
history of exposure or vitamin D assay
How is vitamin D toxicosis treated?
non-specific treatment of hypercalcemia + salmon calcitonin
What are some non-specific treatments for hypercalcemia?
IV fluids, furosemide, biphosphonates, and glucocorticoids
What is hypocalcemia?
When blood ionized calcium levels decrease - PTH rises, Vitamin D conversion occurs, increased GI calcium absorption, decreased renal calcium excretion, and calcium mobilized from bones
What are the etiologies for hypocalcemia?
LEANCHAP - Lack of PTH, Eclampsia, Acute renal failure, Renal, Chronic kidney disease, Hypoalbuminemia, Acute pancreatitis, and phosphate enemas
Also - Sepsis, malabsorption, and blood transfusions
What clinical signs are associated with hypocalcemia?
Seizure/tetany, stiff gait, muscle fasciculations, hyperthermia, cardiac arrhythmias, facial pruritus, and chewing on paws
What is hypoparathyroidism?
Lack of PTH due to loss of functional parathyroid tissue
What are the causes of hypoparathyroidism?
Iatrogenic with thyroidectomy, parathyroidectomy, and primary immune-mediated destruction
When should you have a high index of suspicion in hypoparathyroidism cases?
Profound hypocalcemia, hypomagnesemia, hyperphosphatemia, normal renal parameters, and low to undetectable PTH levels in the face of hypocalcemia
What is the goal of hypoparathyroidism treatment?
To increase calcium level to a point that eliminates clinical signs
What is the emergency treatment for hypocalcemia?
IV calcium administration very slowly to avoid causing arrhythmias
What is the chronic therapy for hyothyroidism?
oral calcium, vitamin D (calcitriol), and to treat the clinical signs
What is eclampsia?
Hypocalcemia resulting from lactation and calcium loss into milk
