Nephrology Flashcards
What is the pathophysiology of neprotic syndrome?
Description of a group of associated symptoms
Results from some form of injury to the podocytes (often due to immune complex or complement deposition). This damages their capacity to prevent protein +/- blood from crossing the glomerulus (loss of anionic charge), allowing protein to leak into the urine. This results in loss of oncotic pressure within the plasma, causing fluid to leak into tissues.
Why do those with nephrotic syndrome tend to have hypoalbunaemia?
Due to urinary losses of protein, although a contribution from protein catabolism by tubular epithelial cells may also be relevant.
White bands in the nails (Muehrcke’s bands) are a characteristic sign of hypoalbuminaemia.
Why can hypercholesterolaemia and hypercoagulability occur in nephrotic syndrome?
In response to hypoalbuminaemia, there is a non-specific increase in liver protein synthesis in an attempt to compensate. However, by doing this, it also increases it’s synthesis of lipoproteins and clotting factors. As these are not lost in the urine, they accumulate, causing hyperlipidaemia and hypercoagulability
Why does oedema occur in nephrotic syndrome?
Underfill Model
- Reduced oncotic pressure leads to fluid shift from vascular to extracellular fluid compartment.
- Reduced PV stimulates activation of RAAS and release of ADH -> sodium and water reabsorption in the distal nephron.
- Capillary hydrostatic pressure is increased -> promotes further fluid shift into extravascular space
Overfill model
- Results from defect of sodium excretion in distal nephron.
- Sodium retention -> increased blood volume due to suppressed vasopressin and angiotensin/aldosterone levels.
- Increased capillary hydrostatic pressure and low oncotic pressure favours fluid movement into the extravascular space
What are clinical signs of nephrotic syndrome in children?
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Oedema
- Periorbital (earliest sign)
- Scrotal, vulval, leg, ankle
- Ascites
- SOB - due to pleural effusions + abdominal distention
- Infections - loss of protective immunoglobulins in urine
- Frothy urine - due to albumin/lipurea
- May have haematuria
- GI disturbance
- Anorexia
What investigations would you do if you thought that a child had nephrotic syndrome?
- Bloods - FBC, ESR, U+Es, creatinine, albumin, complement C3/4
- Urine dipstick - Protein ++++
- Protein-Creatinine ratio
- 24 hr urine collection (GOLD STANDARD)
- Urine microscopy and culture
- Hep B/C screen
What is normal for protein/creatinine ratio?
<20mg/mmol
What is regarded as being in the nephrotic range when looking at protein creatinine ratio?
>200mg/mmol
For 24 hour urine collection, what is regarded as being a normal level of protein in the urine?
<60mg/m2/24 hrs
For 24 urine collection, what is regarded as being in the nephrotic range for protein in the sample?
>1g/m2/24hrs
What are the main causes of nephrotic syndrome in children?
-
Steroid sensitive
- Minimal change disease
-
Steroid resistant
- Focal segmental glomerulosclerosis
What is minimal change disease?
There is diffuse loss of podocyte foot processes (known as effacement). This is thought to occur due to abnormal secretion lymphokines by T cells, which leads to a reduction in electrostatic repulsion of negatively charged molecules (such as proteins) by the podocytes, leading to increased glomerular permeability to certain proteins -> selective proteinuria
What findings would you see on electron microscopy with minimal change disease?
- Podocyte effacement
- Vacuolation
- Microvilli on visceral epithelium
What percentage of those with nephrotic syndrome have steroid sensitive disease?
85-90%
What age range does minimal change disease occur in?
1-10 yrs
What would suggest that it is not minimal change disease causing nephrotic syndrome?
- Evidence of autimmune disease
- Steroid resistance
What clinical features would indicate that the nephrotic syndrome may be steroid sensitive?
- No macroscopic haematuria
- Normal BP
- Normal complement
- Normal renal function
What is the definition of steroid resistant nephrotic syndrome?
Not responding to high dose steroids for 4 weeks
What is the definition of preoteinuria?
>3.5 g protein in 24 hrs
If you had confirmed the nephrotic syndrome as steroid sensitive (i.e. MCD), how would you manage the child?
-
Oral corticosteroids - 8-12 weeks
- 60mg/m2/day - reduce to 40mg/m2/day after 4 weeks
What proportion of steroid sensitive nephrotic syndromes resolves?
95% within 2-4 weeks
What proportion of those with steroid sensitive nephrotic syndrome relapse?
80%, of which 50% are frequent
What are complications of nephrotic syndrome at presentation/relapse?
- Hypovolaemia
- Thrombosis
- Infection
- Hypercholesterolaemia
Why does hypovolaemia occur in nephrotic syndrome?
During the initial phase of oedema, the intravascular compartment becomes depleted. This causes peripheral vasoconstriction and sodium retention. Low urinary sodium and high packed cell volume indicate hypovolaemia
What is a child at risk of in hypovolaemia caused by nephrotic syndrome?
- Shock
- Thrombosis
Why are children with nephrotic syndrome at risk of thrombosis?
Hypercoagulable state caused by:
- Urinary losses of antithrombin III
- Thrombocytosis which may be exacerbated by steroid therapy
- Increased clotting factor synthesis
- Increased blood viscocity
What is hypoalbuminaemia and what does it cause?
Reduced serum albumin concentration -> decreased intravascular oncotic pressure which leads to fluid shifts into ECF
What is the pathophysiology of FSGS?
Podocytes become damaged, allowing proteins and lipids to pass into the urine, resulting in proteinuria and lipiduria. Over time, the accumulation of lipids and proteins around the focally affected areas cause hyalinosis which leads to sclerosis
What are examples of steroid resistant nephrotic syndromes?
- FSGS
- Membranoproliferative glomerulonephritis
- Membranous nephropathy
If treating a child for suspected steroid sensitive nephrotic syndrome, and it didn’t respond to treatment, what would be your next step?
Renal biopsy
What is haematuria?
Urine that is red in colour or tests positive for haemoglobin on urine sticks - should be examined under microscope
Defined as >10 RBCs per high-powered field
How can you distinguish glomerular haematuria from lower urinary tract haematuria?
Glomerular haematuria is more brown (due to deformed RBC’s and casts), and is often accompanied by proteinuria
Lower urinary tract haematuria is bright red, and occurs at the beginning of end of the urinary stream. This is not normally accmpanied by proteinuria
What is the most common cause of haematuria?
UTI - seldom as only symptom
What are causes of proteinuria?
- Orthostatic proteinuria
- Glomerular abnormalities
- Febrile illness - transient
- After exercise - transient
- Increased glomerular filtration pressure
- CKD
- HTN
- Tubular proteinuria
- UTI/STI
What are non glomerular causes of haematuria?
- Infection
- Trauma
- Stones
- Tumours
- Sickel cell disease
- Bleeding disorders
- Renal vein thrombosis
- Hypercalciuria
What are glomerular causes of haematuria?
- Acute glomerulonephritis
- Chronic glomerulonephritis
- IgA nephropathy
- Familial nephritis - alports syndrome
- Thin basement membrane disease
What is nephritic syndrome?
Clinical syndrome which shows signs of nephritis. Defined by haematuria, varying degrees of proteinuria, dysmorphic RBCs, and often RBC casts on microscopic examination of urinary sediment