Crystal Arthropathy Flashcards
What are common crystal deposition diseases characterised by?
Deposition of mineralised material within joints and peri-articular tissue
What is the crystal responsible for gout?
Monosodium urate
What is the crystal responsible for pseudo gout?
Calcium pyrophosphate dihydrate (CPPD)
What is the crystal responsible for calcific periarthritis/tendonitis?
Basic calcium phosphate hydroxy-apatite (BCP)
What are the 2 most common crystal arthropathies?
Gout and pseudogout
What fractions of uric acid in the body comes from dietary purines?
- 1/3
- (2/3 - DNA, RNA, HGPRT)
What is the breakdown process for purines?
purines -> hypoxanthine -> xanthine -> plasma urate
How is uric acid excreted from the body?
- 70% via kidneys
- 30% into the biliary tract (subsequently converted by colonic bacterial uricase to allantoin)
How does hyperuricaemia occur in the vast majority of people with gout?
Reduced efficiency of renal urate clearance
What are the 2 causes of hyperuricaemia?
Overproduction and under-excretion
What are the underlying causes of overproduction?
- Malignancy e.g lymphoproliferative, tumour lysis syndrome
- Severe exfoliative psoriasis
- Drugs e.g. ethanol, cytotoxic drugs
- Inborn errors of metabolism
- HGPRT deficiency
What are the underlying causes of under-excretion?
- Renal impairment
- Hypertension
- Hypothyroidism
- Drugs e.g. alcohol, low dose aspirin, diuretics, cyclosporin
- Exercise, starvation, dehydration
- Lead poisoning
Why is alcohol thought to increase the risk of gout?
As the metabolism of ethanol to acetyl CoA leads to adenine nucleotide degradation resulting in increased formation of adenosine monophosphate, a precursor of uric acid
What is Lesch Nyan syndrome?
Genetic HGPRT deficiency
What are the features of Lesch Nyan syndrome?
•X-linked recessive •Intellectual disability •Aggressive and impulsive behaviour •Self mutilation •Gout •Renal disease
What is the importance of HGPRT deficiency?
- HGPRT - hypoxanthine-guanine phosphoribosyl transferase
- Plays a key role in the recycling of the purine bases (hypoxanthine and guanine) in the purine nucleotide pools
- In absence of HGPRT, the purine bases cannot be salvaged and they are degraded and excreted as uric acid
- There is also an increased synthesis of purines (presumably to compensate for purines lost) which also contributes to the over-production of uric acid
Who gets gout?
- Predominantly older men
- Men always > women
- Men have higher rate levels
How does oestrogen affect uric acid?
It has a uricosuric effect making gout very rare in younger women
How does ageing affect prevalence of gout?
- There is an increased in sUA levels mainly due to reduced renal function
- Increased use of diuretic and other drugs that raise sUA
- Age-related changes in connective tissues which may encourage crystal formation
- Increased prevalence of OA
How is gout diagnosed?
•History •Examination •Differential Diagnosis •Investigations
Where do gout episodes classically occur?
The 1st metatarsophalangeal joint
What is the history of a gout episode?
•Classically overnight onset •May have been on holiday - alcohol and dehydration •Erythema •Unbearably painful •Lasts 5-7 days •If severe - inflammation of the overlying skin •Potentially discharges f chalky material
What are tophi?
A tophus is a massive accumulation of uric acid
Where do tophi occur?
•Bony prominences •Ear
