PATHOLOGY - Polyuria Polydipsia (PUPD) Flashcards
(49 cards)
What is polyuria?
Polyuria is an increase in both the frequency and volume of urine
What is a key factor when supporting PUPD patients?
It is essential to provide PUPD patients with continuous access to water as most PUPD cases begin with polyuria and the polydipsia is secondary to compensate
Really important to get this across to owners as often they will restrict water because they think it will prevent accidents in the house
What is required for the concentration of urine?
Functional nephrons
Generation and persistance of renal corticomedullary gradient
Appropriate renal tubule filtrate osmolality
Production and release of ADH
Response to ADH at the level of the renal tubules
Appropriate water intake
How do the kidneys establish a renal corticomedullary gradient?
For water to be conserved from the renal tubules, a hypertonic medullary interstitium must be maintained. The ultrafiltrate entering the renal tubules has a similar osmolality to plasma. The difference in osmolality between the medullary interstitium and the renal tubular filtrate produce an osmotic gradient allowing for passive reabsorption of water from the decending loop of henle. The ascending loop of Henle is impermeable to water, however it reabsorbs sodium chloride, maintaining the hyperosmolarity of the medullary interstitium. When the urine reaches the collecting duct, it is hyposthenuric. In response to increased plasma osmolality, the pituitary gland releases ADH which triggers urea reabsorption, and increases the permeability of the collecting ducts of the nephrons to increase reabsorption of water into the bloodstream to concentrate the urine
Why is renal tubular filtrate osmolality important for urine concentrating?
The passive reabsorption of water and sodium chloride into the renal medulla depends on the osmolality of the renal tubular filtrate. Should the renal tubular filtrate have a higher osmolality, the gradient between the renal tubular fluid and medullary interstitium may no longer facilitate passive reabsorption of water and solutes
What are the differential diagnoses for PUPD in dogs?
Diabetes mellitus
Chronic renal failure
Hyperadrenocorticism (Cushing’s disease)
Hypercalcaemia
Neoplasia
Hepatic failure
Pyogenic foci
Hypoadrenocorticism (Addison’s disease)
Diabetes insipidus
Psychogenic polydipsia
What are the differential diagnoses for PUPD in cats?
Chronic renal failure
Hyperthyroidism
Diabetes mellitus
Pyogenic foci
Hepatic failure
Neoplasia
Hypercalcaemia
Diabetes insipidus
How does diabetes mellitus cause PUPD?
Diabetes mellitus results in glucosuria. Glucose is a high molecular weight substance resulting in the increases osmolality of the renal tubular filtrate and consequently will generate an osmotic gradient where water is moved into the tubules rather than reabsorbed into the plasma, resulting in PUPD
How does hyperthyroidism cause PUPD?
Hyperthyroidism results in an increased metabolic rate, increased cardiac output and thus increased renal blood flow and glomerular filtration rate, resulting in increased urine production and polyuria. This chronic polyuria can result in renal medullary washout, resulting in reduced urinary concentration and further PUPD
How does renal failure cause PUPD?
Renal failure causes a loss of functional nephrons which decreases urine concentrating ability, resulting in PUPD
How does cushing’s disease cause PUPD?
Cushing’s disease results in increased serum cortisol levels, and cortisol results in a failure of the nephron to respond to ADH
How does hypercalcaemia cause PUPD?
Hypercalcaemia results in a failure of the nephron to respond to ADH
How does hepatic failure result in PUPD?
When the liver is dysfunctional, there will be reduced conversion of ammonia into urea resulting in low serum urea levels. Urea is a major component of the hypertonic renal medullary interstitium and thus without the corticomedullary gradient, the urine cannot be concentrated, resulting in PUPD
How does addison’s disease cause PUPD?
Addison’s causes reduced aldosterone production resulting in decreased renal sodium reabsorption, resulting in hyponatremia and thus the loss of the hypertonic medullary interstitium and renal concentrating ability, resulting in PUPD
Which history questions are important when investigating PUPD?
Have there been any behavioural changes? (i.e. is the dog lethargic, normal, had any episodes of collapse etc)
How is the patient’s appetite?
Have you noticed any weight loss?
Have there been any dermatological changes?
Has there been any vomiting or diarrhoea?
Has there been any discharge?
Is the patient on any medications?
Recent medical history?
What is the volume, frequency and timing of urination? (try to differentiate between PUPD, pollakuria and urinary incontinence)
Which drugs can result in PUPD?
Diuretics
Corticosteroids
What should you particularly focus on when doing a clinical examination on a PUPD patient?
Full clinical examination
Lymph nodes
Dermatological changes
Assess for purulent discharges (vulva, anus, prepuce)
Abdominal palpation
Rectal examination
Thyroid palpation
Why is a rectal examination particularly important when investigating PUPD?
A rectal examination is particularly important when investigating PUPD as anal sac adenocarcinomas can cause hypercalcaemia and consequently PUPD
Which initial diagnostic tests can you do when investigating PUPD?
Urinalysis
Biochemistry
Haematology
Which differential diagnoses can be ruled out based on a urine specific gravity (USG)?
- PUPD can be ruled out if the USG is above 1.035 as the body is incapable of producing large volumes of concentrated urine
- Isosthenuria and hypersthenuria rules out diabetes insipidus as this would result in hypostheuria (however be aware that hyposthenuria does not confirm a diagnosis of diabetes of insipidus)
Which differential diagnoses can be ruled out based on a urine dipstick?
No glucose in the urine can rule out diabetes mellitus
Which parameters should you assess on biochemistry when investigating PUPD?
Glucose
Calcium
Urea
Creatinine
Electrolytes (sodium, potassium, chloride)
Phosphate
Thyroid hormones
Which parameters are the most important to assess on biochemistry when investigating PUPD?
Glucose
Calcium
What can be indicated by a mild hyperglycaemia on biochemistry?
Mild hyperglycaemia can indicate stress, however this is not a cause of PUPD
