Urinary 7 - Urinary Stones Flashcards
In what form is Calcium and Phosphate stored in bone?
Hydroxyapatite crystals [Ca10(PO4)6(OH)2]
How many grams of Calcium is stored within an adult skeleton and teeth?
~1000g
Which 2 hormones control serum calcium levels?
1) Parathyroid hormone
2) Calcitriol
What stimulus causes increased secretion of PTH?
Fall in serum Calcium levels
What tissues does PTH affect?
Kidneys
Bones
What affect does PTH have on the kidneys?
- Increases Calcium resorption
- Decreases Calcium excretion
- Increases conversion of Calcidiol to Calcitriol via 1alpha-hydroxylase
What affect does PTH have on bones?
- Increases osteoclast activity = increased bone resorption
- Decreases osteoblast activity
How does Calcitriol increase serum Calcium levels?
Acts on bone: Increases Osteoclast activity
Acts on small intestine: Increases Calcium absorption
How does Calcitriol increase Calcium absorption from the small intestine?
Increases the expression of Calcium Binding Proteins on apical gut wall
What enzymes converts Calcidiol to Calcitriol?
1alpha-hydroxylase
What is the function of 1alpha-hydroxylase?
Converts Calcidiol to Calcitriol
Where does the majority of Calcium and Phosphate resorption take place?
Proximal Convoluted Tubule
What are the 4 types of Calcium stones?
1) CaOx + CaP
2) CaP only
3) Struvite (Magnesium Ammonium Phosphate Hexahydrate)
4) Uric acid
Name 3 types of stones which are not made up of Calcium:
1) Cysteine stones
2) Drug stones
3) Ammonium acid urate stones
Name 3 drugs which may cause urinary stones:
1) Indinavir (for HIV)
2) Triamterene (Diuretic)
3) Sulphadiazine (Antibiotic)
What are the most common causes of hypercalcaemia?
- Primary hypersecretion of PTH
- Destruction of bone tissue due to Myeloma or diffuse metastases
What is the most common type of urinary stone?
CaOx + CaP
Give 5 symptoms of hypercalcaemia:
1) Painful bones
2) Abdominal groans
3) Renal stones
4) Psychic moans
5) Severe muscle weakness
Are urinary stones more common in men or women?
Men 2:1
Except struvite stones which are more common in women due to increased incidence of UTIs in women
Which urinary stone can grow very quickly?
Struvite stones
What causes a Struvite stone?
Bacterial UTI, with bacteria which have Urease
What type of stone is often caused by hyperparathyroidism, or renal tubular acidosis?
CaP only stones
Name some causes of hypercalciuria:
- Increased Calcium absorption from GIT
- Increased Calcium resorption from bone (immobilisation/weightlessness)
- Excessive dietary Calcium intake
- Hypercalcaemia
What type of diuretics can cause hypercalcaemia?
Thiazide diuretics
Name some causes of hyperoxaluria:
- Primary = rare autosomal recessive genetic disorder
- Increased intestinal Oxalate absorption (secondary to Crohns post resection usually)
- Increased Oxalate intake and decreased Calcium intake
Name some foods high in Oxalate:
Tea
Rhubarb
Spinach
Nuts
What are the 2 common causes of CaP-only urinary stones?
1) Hyperparathyroidism
2) Renal tubular acidosis
What condition predisposes to cysteine stones?
Cysteinuria
Rare genetic disorder
What is Milk-Alkali syndrome?
Excessive intake of Calcium and absorbable alkali, resulting in hypercalcaemia, metastatic calcification and renal failure. Most commonly caused by post-menopausal women ODing on Calcium supplements
Who is particularly at risk of developing uric acid stones?
- Gout sufferers
- People with an increased cell turnover (Lympho-/Myelo-proliferative disorders, or chemotherapy patients)
- Dehydrated people
What is the most common bacteria which causes Struvite stones?
Proteus mirabilis
What shape do Struvite stones usually take, and where do they develop?
Staghorn shape
Renal pelvis and several calyces
Who are predisposed to UTI’s?
- Women (shorter urethra)
- Spinal cord injury
- Neurogenic bladder
- Vesicoureteric reflux
- Obstructive uropathy (enlarged prostate/pregnancy/stones/tumours)
Describe renal colic:
Excruciating pain from flank radiating to iliac fossa or inner thigh (L1 distribution)
Bouts ~ 20-60 min
Untreated usually subsides within ~ hrs
Often with nausea/vomiting/pallor/sweating/restlessness/haematuria
What causes renal colic?
Ureteric stone
Peristaltic contractions or spasm of ureter trying to expel stone
What is the name of the pain associated with a ureteric stone?
Renal colic
What type of pain is associated with a kidney stone?
Dull loin ache
What is the maximum diameter of a urinary stone which can be passed?
< 5 mm
At what diameter do urinary stones usually require intervention?
> 7 mm
List some presentations associated with a urinary stone:
- Man (or woman with recurrent UTIs)
- Renal colic or dull loin ache
- Urinary retention
- Haematuria
- Renal failure (fluid retention, drowsiness, SOB, fatigue, nausea)
Why are many sufferers of urinary stones resistant to increasing their water intake?
Causes increased pain
- Most have urinary retention due to obstruction, so more fluid will increase the pain
- May be painful to urinate due to inflammation from obstruction/UTI
What does MSU stand for?
Mid-Stream Urine sample
Why would you want an MSU from a patient with suspected urinary stone?
Microscopy for casts/RBCs/crystals
Culture bacteria
What type of stones are radio-opaque?
- CaOx + CaP
- CaP-only
- Struvite
What type of stones are radio-lucent?
- Uric acid stones
- Triamterene stones
Name some investigations performed when urinary stones suspected:
- MSU (culture/microscopy)
- Plain abdo X-Ray
- Ultrasound
- CT scan of kidney, ureter and bladder
- Blood: FBC, CRP, renal function, electrolytes, calcium, phosphate and urate, creatinine
- Ureteroscopy
List some complications of urinary stones:
- Acute pyelonephritis +/- septicaemia (Gram +ve)
- Pressure necrosis of renal parenchyma
- Urinary obstruction –> hydronephrosis
- Ulceration through wall of collecting system
What are the management options for someone with a urinary stone?
- Analgesia (IV Diclofenac/Pethidine if in hospital, or NSAIDs if not)
- Percutaneous nephrolithotomy
- Extracorporeal Shock Wave Lithotripsy (ESWL)
Describe ESWL (Extracorporeal Shock Wave Lithotripsy):
External focused high-intensity ultrasonic waves used to break up stones near renal pelvis
~ 30-60 mins
What does ESWL stand for?
Extracorporeal Shock Wave Lithotripsy
Which analgesia is usually given to patients admitted to hospital with a painful urinary stone?
IV Diclofenac/Pethidine
Potassium citrate salts may promote the formation of which type of stones?
CaP-only
How do Thiazide diuretics decrease the excretion of Ca2+?
Increase Ca2+ reabsorption
Name some urinary stone preventions:
- Increase water intake
- Thiazide diuretics (decrease Ca2+ excretion)
- Potassium citrate to alkalinise urine (can induce CaP stones)
