crystal arthropathy Flashcards
what is the normal function of crystals within the body?
to strengthen the skeleton
to attract XS ions for removal from the body
describe what a crystal is
a homogenous solid where the ions are bonded closely in an ordered, repeating, symmetric arrangement
stable
hard
high density
what is a crystal arthropathy?
arthritis caused by crystal deposition in the lining of the joint
Describe the crystals seen in gout
negatively birefringent
needles
Describe the crystals seen in pseudogout
positively birefringent
rhomboids
more sparse distribution under the microscope
What is the name given to the crystals in gout?
monosodium urate crystals
what is the name given to the hard deposits formed in chronic gout?
tophaceous gout / tophi
What should you be concerned about when you see gout in a young person?
inborn metabolic errors
What is the most commonly affected joint in gout?
the first metatarsophalangeal joint (ie base of the big toe_
Name some joints that gout can affect
big toe ankle/foot knee finger elbow wrist
what is the key enzyme in the uric acid formation pathway that can be targeted by treatment?
xanthine oxidase
What is the serum level of uric acid that under which, there is negligible risk of gout?
0.3 mmol/L
At what serum level of uric acid is there some risk of crystal deposition?
0.36 mmol/L
at what level of uric acid is the serum supersaturated and urate crystal deposition likely?
0.42 mmol/L
What is the primary method of excretion of uric acid?
renal
What are the sources of purines in the body
diet
purine synthesis
tissue nucleic acids eg DNA and RNA
What does xanthine oxidase do?
converts purines to uric acid
specifically converting purines to hypoxanthine and hypoxanthine to xanthine
What type of cells are responsible for the inflammatory response seen in gout?
WBCs eg macrophages
What is the main reason for hyperuricaemia?
underexcretion of uric acid
What is the major risk factor for gout?
hyperuricaemia
when would you not measure the level of uric acid in the blood?
during an acute attack as it can be paradoxically low
List some causes of under excretion of uric acid
alcohol renal impairment hypertension metabolic syndrome obesity diabetes drugs: low dose aspirin, diuretics esp thiazides, cyclosporin, tacrolimus, ethambutol and pyrazinamide
What are the causes of overproduction of uric acid?
alcohol drinks
diet - XS meat, shellfish, offal, fructose sweetened
metabolic syndrome
myeloproliferative disease and cytotoxic drugs
psoraisis
Name a differential diagnosis of gout and why it is a differential
joint sepsis - it is the only other condition where the skin is red and shiny
What are the common precipitants of an attack?
aggressive treatment for hypouricaemia alcohol or shellfish binges sepsis acute MI dehydration
What is the appearance of gout on XR?
punched out periarticular erosion
joint space narrowing
soft tissue calcification and crystal deposition
What is the long term preventative treatment for gout?
allopurinol or febuxostat ie the xanthase oxidase inhibitors
what must you do when you start sb on long term preventative treatment for gout?
Give them drugs for acute gout treatment initially as starting sb on preventative treatment can precipitate a gouty attack - so start on colchidine or NSAID
what is the aim of preventative treatment?
To bring serum uric acid level to <300mmol/L
What is the principle for allopurinol dosing?
start low, go slow - aka start with a low dose and titrate upwards according to the serum uric acid level
What would you do if you were giving allopurinol to sb with renal failure and why?
reduce the dose - as allopurinol is excreted by the kidneys and if the kidneys can’t excrete, then levels of the drug build up in the body
What is the name given to the crystals deposited in pseudogout?
calcium pyrophosphate crystals
What are the typical joints affected by pseudogout?
the MCPs in the hand wrists knees ankles most common in knee
How does pseudogout present?
acute monoarthritis severe pain stiffness swelling redness
How would you distingush OA from pseudogout?
pseudogout:
joints that are involved
inflammation - 4 pillars
superimposition of acute attacks on chronic
What are the triggers of an acute attack in pseudogout?
direct trauma to the joint
surgery
blood transfusion, IV fluid
spontaneous - no obvious trigger
What would an XR of the knee show in pseudogout?
chondrocalcinosis - deposition of calcium in the cartilage
Name some metabolic disorders that may be associated with pseudogout esp. in a young person?
haemochromatosis
hyperparathyroidism/hypoparathyroidism
acromegaly
hypomagnesaemia and hypophosphataemia
How is pseudogout managed?
acute attacks - NSAIDs, analgaesia, aspirate the joint and give steroid injections
long term - trial of methotrexate, hydrochloroquine, synovectomy or surgery
What is the critical diagnostic test in gout/pseudogout?
joint aspiration!
Give some points you would mention to a pt to educate them about prevention of gout
prevent dehydration lose weight reduce alcohol intake reduce red meat intake add more dairy products to the diet
