Crystal Arthropathy Flashcards
Gout Pseudogout Polymyalgia Rheumatica
Presentation of gout
1st MTP most common (can be around other joints)
Swelling and redness over joint
Very painful sudden onset in morning
Untreated lasts 7-10 days before settling
What are tophi
Massive accumulations of uric acid found on bony prominences, form if persistently high levels of uric acid and gout
How is purine related to gout
Purine (2/3 from DNA breakdown, rest from diet) is broken down into urate which is mostly excreted in the kidney and rest from biliary tract by colonic bacterial uricase to allantoin.
How do high levels of urate cause gout
If too much rate is made and not enough excreted plasma urate levels rise and crystals form around joints - it becomes acute gout when it builds up and breaks through the joint, irritating the synovium and becoming symptomatic
What is usually the cause of hyperuricaemia
Decreased efficiency of renal urate excretion
Hyperuricaemia causes
Overproduction
- malignancy (lymphoproliferative, tumour lysis syndrome)
- Severe exfoliative psoriasis
- Drugs (ethanol, cytotoxic drugs)
- Inborn errors of metabolism
- HGPRT deficiency
Underproduction
- Renal impairment
- HTN
- Hypothyroidism
- Drugs - alcohol, low dose aspirin, diuretics, cyclosporin
- Exercise, starvation, dehydration
- Lead poisoning
How is alcohol related to gout
Alcohols are rich in purines (i.e. beer contains guanine) and ethanol –> acetyl CoA which leads to adenine nucleoside degeneration resulting in increased adenosine monophosphate formation (precursor of uric acid)
Alcohol also increases lactic acid level in the blood leading to inhibition of uric acid excretion
What is Lesch Nyan syndrome
HGPRT deficiency, x-linked recessive intellectual disability causing:
- aggressive and impulsive behaviour
- self-mutilation
- gout
- renal impairment
What does HGPRT do
Role in recycling of purine bases
Without it they are excreted as uric acid
Triggers of gout
Obesity Alcohol Increased cholesterol and BP Diuretics Dehydration
Which sex does gout usually affect and why
Males - they have higher urate levels and oestrogen has a uricosuric effect
Why is ageing a risk factor for gout
- Increased sUA mainly due to reduced renal function
- Increased diuretic use and drugs which increase sUA
- Age-related connective tissue changes which can encourage crystal formation
Diagnosis of gout
Hx and Exam - 1st MTP (obviously gout), Knees and ankles (could be a septic joint)
Investigations
- Aspiration (see crystals and exclude infection)
- Gram stain and culture (infection)
- Polarising Microscopy (crystals)
What is the main crystal seen in gout
monosodium urate
Management of acute flare of gout
NSAIDs
Colchicine (can cause diarrhoea and takes longer to work)
Steroids (IA, IM, oral) - 2nd line
When to treat hyperuricaemia
If 2 symptomatic attacks in 1 year Prophylactically prior to treating certain malignancies 1st attack if: - single attack of polyarticular gout - tophaceous gout - urate calculi - renal insufficiency
Wait until acute attack has settled before trying to reduce urate levels with allopurinol as can trigger an attack of gout
Treatment of hyperuricaemia
Allopurinol (xanthine oxidase inhibitor) - 1st line
Febuxostat (same as above but metabolised by liver instead of kidney)
Uricosuric agents (sulphinpyrazone, probenecid) - 2nd line
Address lifestyle factors
- HTN, smoking, fizzy drinks, alcohol, obesity, purine rich foods, dehydration, more F&V (cherries), yoghurt
Presentation of pseudogout
Affects knee
Mainly in elderly females
Triggered by trauma or intercurrent illness
What crystal is commonly found in pseudo gout
Calcium pyrophosphate dihydrate (CPPD)
Investigations for pseudo gout
X-ray - if trauma in person with acutely swollen joint, shows chondrocalcinosis commonly in knee and wrist
Aspiration - shows pyrophosphate crystals on microscopy (rhomboid shape, positively birefringent)
Management of pseudo gout
NSAIDs IA steroids (if confident of no infection) Rest, Splinting, analgesia
What is polymyalgia rheumatica
Inflammatory condition of elderly (females>males)
Presentation of polymyalgia rheumatica
SUDDEN onset STIFFNESS of shoulder / pelvic girdle
Malaise, weight loss, fever, depression
Arthralgia, synovitis occasionally
What is polymyalgia rheumatic associated with
GCA
- 20% with PMR may have GCA
- 50% with GCA may have PMR
High ESR, anaemia
Diagnosis of polymyalgia rheumatica
By history
- Age >50
- ESR >50
- Dramatic steroid response within ~24-48hours
Treatment of PMR
Prednisolone 15mg per day for 18-24 months
Bone prophylaxis as on long term steroids (bone loss greatest in 1st 3 months of onset of steroids) - do DEXA scan
Differential diagnosis of PMR
Myalgic onset inflammatory joint disease
Malignancy (multiple myeloma, lung cancer)
Hypo and Hyperthyroidism (check TFTs)
Inflammatory muscle disease (check creatinine)
Bilateral Shoulder Capsulitis (Frozen shoulder) - more mechanical pain
Fibromyalgia
