Crystal arthritis Flashcards
Which diseases come under ‘crystal arthritis’?
- Gout
- Pseudogout
Which crystals precipitate in gout?What kind of birefringence does it have? what is the shape of the crystals?
- Urate crystals
- Negatively birefringence
- Long & needle shaped
Which crystals precipitate in pseudogout?What kind of birefringence does it have?What is the shape of the crystals?
- calcium pyrophosphate crystals
- positively birefringence
- Small rhomboid shaped
What are the characteristics of gout
- Tends to be acute monoarthritis
- Typically occurs in a peripheral joint, particularly the big toe
- When it happens, people are usually feeling well the day before i.e it is sudden
- Max peak of pain tends to peak during 24 hours
What is a common differential of gout?
Septic arthritis (but with this people usually describe a prodrome of feeling systemically unwell)
What is the role of uric acid in gout?
-Uric acid is the final product of purine metabolism
Why can’t humans break down uric acid in the body?
-Humans have inactive uricase gene
Outline the metabolism of purines
Hypoxanthine—> Xanthine (using enzyme Xanthine oxidase)
Xanthine—> Uric acid (using enzyme Xanthine oxidase)
What is the threshold(s) for hyperuricaemia
- In males is >0.42mmol/L
- In females is .0.36mmol/L
- Hyperuricaemia is more common than gout
What are the risk factors for development of gout?
- Hyperuricaemia
- Persistent alcohol consumption
- Diuretic use
- High BMI
- Lipid disorders
- Older age
- Male sex
- Genetics
Outline a high urate diet
- Shellfish(esp oysters)
- Marmite
- Red meat
- Beer(real ale)
- alcohol
- sweetened soft drinks
What can reduce fractional clearance of urate?
- Alcohol
- Donate a kidney/ have CKD
- Use of diuretics
What are the clinical features of gout
- Classic description of severe pain of rapid onset
- First attack always single joint and never axial skeleton
- Great toe MTPJ>50%
- BUT subsequently any joint/any number of joints
Define Gouty Tophi
- aka tophaceous gout
- A deposit of uric acid crystals, in the form of monosodium urate crystals
- in people with longstanding hyperuricaemia
- pathognomic for the disease
Where can Gouty Tophi typically occur
- Fingers
- ears
- bursae eg olecranon bursa
How can we distinguish between the radiographical features of gout and RA?
Gout: -periarticular 'hole punched' out lesions RA: -Marginal erosions -Not periarticular -On the joint margin
Can we distinguish between gout and septic discitis radiographically?
- NO
- Gout that has spinal involvement ( which may or may not be at multiple disc levels) cannot be radiographically distinguished from a septic discitis
How is gout diagnosed?
-Arthrocentesis
Outline the therapeutic strategies in gout
- ) Dietary restriction to reduce exogenous purines:
- eg less oysters & red meat - )Xanthine oxidase inhibitors: reduce the formation of urate; this reduces endogenous purines
- ) Recombinant uricase:
- reduces the formation of precipitates as this is more soluble
- but when you stop it it can cause rebound hyperuricaemia so we barely use these - ) Uricosuric agents:
- drugs that increase renal clearance
- But gout patients typically have renal insufficiency or failure so these agents would be useless in these pts
Outline the drugs we may use to relieve pain in gout?
- ) NSAIDs
- Most common as long as pt is healthy
- eg Naproxen 500mg bd x5d
- Avoid in renal, cardiac or liver disease - ) Colchicine:
- 1 mg STAT; 0.5mg bd x5d
- Beware of interactions - ) Prednisolone:
- 30mg od x5d
- Caution in DM/CCF
List the contraindications of NSAID use
don’t use in the following diseases…
- renal
- cardiac
- liver
What drugs are used to prevent recurrence of gout?
URATE LOWERING THERAPY: Xanthine oxidase inhibitors...(beware of azathioprine/6-MP) 1.) Allopurinol: -some pts get a rash -risk of DRESS 2.) Febuxostat -Beware theophylline
What does DRESS stand for and what isit
- Stands for drug reaction with eosinophilia and systemic symptoms
- rare, potentially life-threatening
- drug-induced
- hypersensitivity reaction
- Includes skin eruption, hematologic abnormalities, lymphadenopathy& internal organ involvement
Why should we beware of axathioprine/6-MP when using xanthine oxidase inhibitors
- 6-MP is the active metabolite of azathioprine
- azathioprine is metabolised by xanthine oxidase so if you co-prescribe, you will no longer be able to metabolise it
What are the risk factors for calcium pyrophosphate disease(pseudogout)
- ageing
- prior joint trauma
- familial chondrocalcinosis
- Haemochromotosis
- Hyperparathyroidism,hypomagnesemian and hypophosphatasia (inc Gitelman’s syndrome)
define chondrocalcinosis
calcium within the joint
What are the characteristics of CPPD
- Mono or oligoarticular disease
- Rapid onset severe joint pain
- Peak intensity within 6-24hrs(earlier than gout)
- fever in majority of pts (in contrast gout pts rarely get a fever, or are unaware of it if they do)
- overlying erythema & desquamation
- Resolution in 3-4days
What does CPPD stand for?
Calcium pyrophosphate deposition disease
compare and contrast gout crystals with those of CPPD
CPPD crystals are:
- positively birefringent
- tend to be sparse in number
- smaller
- more weakly birefringent
Outline the treatment of CPPD
- pretty much the same as gout
- Currently we have no treatment that prevents long term recurrence of the disease
- If there is significant OA you can do a joint replacement
