Crystal Arthropathies Flashcards
What are the common crystal deposition diseases?
Monosodium urate - gout
Calcium pyrophosphate dehydrate - pseudo gout
Basic calcium phosphate hydroxyl-apatite - calcific periarthritis/tendonitis
What are crystal deposition diseases characterised by?
Deposition of mineralised material within joints and peri-articular tissue
What are the features of gout?
Characteristically affects the first MTP joint, also commonly affects elbows
Generally acute onset - patient might go to bed with slight pain and wake up with flare of gout
May be confused with cellulitis but antibiotics will not help
Deposition of uric acid crystals - may be mistaken for pus, can leak, generally deposited over bony prominences = gout tophi
How do you diagnose gout?
History
Examination
Gold standard investigation is to aspirate gout fluid and look under microscope for crystals
Serum urate can be useful in chronic setting once a flare-up has settled
How long do gout flare ups tend to last?
Flares tend to last 3-10 days and settle spontaneously
What joint is most commonly affected by pseudogout?
Knee
What are the features of pseudogout?
Typically elderly females - fall/UTI causing admission
Erratic flares
What is the aetiology of pseudogout?
Idiopathic
Familial
Metabolic
What are the triggers of pseudogout?
Trauma
Intercurrent illness
When are x-rays useful in pseudogout?
Useful to exclude trauma and look for chondrocalcinosis but generally not otherwise useful in acute setting
What is the management of an acute flare of gout?
NSAIDs
Colchicine - can precipitate renal failure, be wary in patients with impairment
Steroids - IM, intra-articular or oral, direct injection useful for knees/wrists/ankles, oral useful for polyarticular
What is the management of pseudogout?
NSAIDs
Intra-articular steroids
No prophylactic therapies
Endogenous production of uric acid from degradation of purines usually contributes to how much of the body urate pool?
2/3
The remainder from diet
Where is the majority of uric acid that is produced daily excreted?
Via the kidney (about 70%)
The remainder is eliminated into the biliary tract and subsequently converted by colonic bacterial uricase to allantoin
In the vast majority of people with gout, hyperuricaemia results from what?
Reduced efficiency of renal urate clearance
What are the causes of over-production of uric acid?
Malignancy Severe exfoliative psoriasis Drugs e.g. ethanol, cytotoxic drugs Inborn errors of metabolism HGPRT deficiency
What are the causes of under-excretion of uric acid?
Renal impairment Hypertension Hypothyroidism Drugs Exercise, starvation, dehydration Lead poisoning
Why is alcohol thought to increase the risk of gout?
Because the metabolism of ethanol to acetyl CoA leads to adenine nucleotide degradation, resulting in increased formation of adenosine monophosphate, a precursor of uric acid
Alcohol also raises lactic acid level of the blood which inhibits uric acid excretion
What are the features of Lesch Nyan Syndrome?
HGPRT deficiency X-linked recessive Intellectual disability Aggressive and impulsive behaviour Self-mutilation Gout Renal disease
What is the enzyme defect in Lesch Nyan Syndrome?
Enzymatic defect is deficiency of the enzyme hypoxanthine-guanine phosphoribosyl transferase which normally plays a key role in the recycling of the purine bases, hypoxanthine and guanine, into the nucleotide pools
What is the management of hyperuricaemia?
Consider if treatment is needed
First attack not treated unless;
- single attack of polyarticular gout
- tophaceous gout
- urate calculi
- renal insufficiency
Treat if there is a second attack within 1 year
Prophylactic treatment prior to treating certain malignancies
Do not treat asymptomatic hyperuricaemia
What is the treatment for lowering uric acid?
Xanthine oxidase inhibitor e.g. allopurinol first line
Febuxostate
Uricosuric agents e.g. sulphinpyrazone
Canakinumab
What are the rules for lowering uric acid?
Wait until the acute attack has settled before attempting to reduce the urate level
Use prophylactic NSAIDs or low dose colchicine/steroids until urate level is normal
Adjust allopurinol dose according to renal function
Prophylactic treatment can be withdrawn once allopurinol is stable
Address cardiovascular and lifestyle factors/risks
What is the presentation of polymyalgia rheumatica?
Sudden onset of shoulder +/- pelvic girdle stiffness Rare in < 50s, usually > 70s ESR usually > 45, often > 100 Anaemia Malaise, weight loss, fever, depression Arthralgia Occasionally synovitis Generally won't have arthritis
What are the similarities between polymyalgia rheumatica and giant cell arteritis?
Both characterised by high ESR and anaemia and both affect elderly women
How do you diagnose polymyalgia rheumatica?
Compatible history Age > 50 ESR > 50 Dramatic steroid response - can be used as diagnostic test, if no reaction then very unlikely to be polymyalgia rheumatica No specific diagnostic test
What are the differential diagnoses for polymyalgia rheumatica?
Myalgic onset inflammatory joint disease
Underlying malignancy e.g. multiple myeloma
Inflammatory muscle disease
Hypo/hyperthyroidism
Bilateral shoulder capsulitis
Fibromyalgia
What is the treatment of polymyalgia rheumatica?
Prednisolone 15mg per day, tapered down slowly over 18-24 month course
Bone prophylaxis
