Renal (Other conditions) Flashcards
Renal artery stenosis (RAS)
describes the narrowing of the renal arteries and is most commonly due to atherosclerosis, followed by fibromuscular dysplasia (FMD). RAS generally presents with accelerated or difficult-to-control hypertension.
Pathogenesis of hypertension in RAS
Narrowing of the renal artery lumen can lead to decreased perfusion to the kidneys. This leads to the activation of the renin-angiotensin-aldosterone system (RAAS) which leads to the secretion of renin. Renin converts angiotensinogen to angiotensin I, which is then converted to angiotensin II by angiotensin-converting enzyme (ACE). Angiotensin II acts on the adrenal glands leading to aldosterone secretion, which leads to sodium and water retention and increased blood pressure.
Renal artery stenosis in <30
fibromuscular dysplasia
Renal artery stenosis in >55
suggests RAS due to atherosclerosis
presentation of RAS
many asymptomatic or only have hypertension
- Severe, accelerating, and/or difficult-to-control hypertension
- Biochemical and/or clinical evidence of renal dysfunction when starting ACE inhibitors or angiotensin II receptor blockers (ARBs) – they reduce renal perfusion even more
- Sudden or unexplained recurrent acute heart failure in a hypertensive patient (‘flash’ pulmonary oedema)
investigations for RAS
UEs
- urea and creatinine may be deranged
- potassium may be low or low-normal due to RAAS activation
Aldosterone:renin ration
- >20 (renin>aldosterone) -> rules out primary hyperaldosteronism
CT angiography or MR angiography
- first line if FMD suspected
- may show string of beads appeaance
management of RAS
Management involves optimising cardiovascular risks (e.g. smoking cessation, control of blood pressure, lipids and blood glucose etc.), avoiding ACE inhibitors or ARBs, and avoiding other nephrotoxic medications. Other management steps include:
- Atherosclerotic RAS: angioplasty with stenting, particularly in flash pulmonary oedema. It may be considered in refractory or severe hypertension
- FMD: percutaneous transluminal angioplasty with balloon dilatation with or without stenting
complications of RAS
- Chronic kidney disease
- Acute kidney injury – e.g. if rapidly worsening or another cause of renal dysfunction is present
- End-organ damage due to hypertension
- Flash pulmonary oedema
Acute interstitial nephritis (AIN)
describes inflammation of the kidney interstitium usually triggered by a hypersensitivity reaction to drugs.
It classically presents with a triad of
- rash
- fever
- eosinophilia
common drugs which can cause acute intestitial nephritis
- Nearly all penicillins and cephalosporins
- NSAIDs
- Rifampicin
- Proton pump inhibitors
- Allopurinol
non-drug causes of AIN
- Infections (e.g. HIV and Epstein-Barr virus (EBV))
- Systemic autoimmune diseases (e.g. systemic lupus erythematosus (SLE) and Sjögren’s syndrome)
- Idiopathic
presentation of AIN
Patients classically have a reduction in kidney function without oliguria within days of starting a causative drug. Other features include:
The classic triad of AIN – rarely appears as all three (<10% of cases):
- Rash
- Fever
- Eosinophilia
- Elevated serum immunoglobulin E (IgE)
acute interstitial nephritis vs acute tubular necrosis
Acute tubular necrosis (ATN)
* Eosinophilia, rash, and elevated IgE make ATN less likely
* Urinalysis may show muddy brown casts in ATN
investigations of AIN
UEs
- urea and creatinine are elevated
Urinalysis
- may show sterile pyuuria - white cells with negative bac culture
- mild- mod proteinuria
Full blood count
- eosinophilia
Trail of discontinuing suspected causative medication
- AKI resolves
Kidney biopy- only test for definitive diagnosis
- only if AKI does not improve when medication stopped or if treatment involving immunosuppessants e.g. steroids is being considered
management of AIN
- Withdrawal of the offending drug
- Supportive care (e.g. correcting derangements in U&Es and fluid balance)
- Corticosteroids may be considered in some cases
complication of AIN
CKD
Acute tubular necrosis (ATN)
is the most common cause of acute kidney injury (AKI). It describes the death of tubular epithelial cells in the kidney and occurs due to ischaemia or nephrotoxic drugs. The presence of ‘muddy brown casts’ is pathognomonic for ATN.