Crystal Arthropathies Flashcards by Aimee Love

What are crystal arthropathies characterised by?

Deposition of mineralised materials within the joints and periarticular tissue

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What is gout?

Inflammatory joint disease where MONOSODIUM URATE crystals are deposited in a joint

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What is the pathophysiology of gout?

Hyperuricaemia (too much uric acid in blood) –> formation of needle-like crystals in area of low BF (joints/kidney tubules)

Purines (from nucleic acid) are broken down into uric acid to be excreted in the urine, however in hyperuricaemia, the level of uric acid exceeds its solubility

XS uric acid loses H to form urate which receives Na to become monosodium urate crystals

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What is the presentation of gout?

1st MTP

Onset overnight, patient’s wake up with v. severe burning pain in joint

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What is the appearance of a joint with gout?

Red, shiny skin over joint

Hot and swollen

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How long does a gout attack last for?

Untreated attack lasts 7-10 days

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What are your DDx for gout?

Septic arthritis (must exclude SA in any monoarthropathy!)
Cellulitis

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What is podagral gout?

Gout of the big toe

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What things are characteristic of chronic gout?

Tophi

Hard chalky nodules caused by deposition of urate crystals in tissues (incl. bone) due to massive accumulations of uric acid
TEND TO BE OVER BONY PROMINENCE (may also be on ear!)

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How do you Rx tophi?

Don’t tend to remove surgically

Just treat underlying gout

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Where does uric acid in the body come from?

2/3rd comes from degradation of purines (from DNA/RNA)

Purines are converted into hypoxanthine and then into xanthine and then into uric acid

Other 1/3rd comes from dietary purines

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How is uric acid normally excreted?

70% via kidney, rest via biliary tract (converted into colonic bacterial uricase to allantoin)

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What are the categories of things that can cause hyperuricaemia?

Overproduction

Underexcretion

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What can cause overproduction of uric acid?

Malignancy 
Severe exfoliative psoriasis 
Drugs
Inborn errors of metabolism 
HGPRT deficiency

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How can malignancy increase risk of gout?

E.g. in lymphoproliferative disorders, tumour lysis syndrome

Faster turnover of cells –> more DNA/RNA broken down –> more purine metabolism

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How does severe exfoliative psoriasis lead to increased risk of gout?

Increased cell breakdown

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What drugs increase risk of gout and why?

Alcohol, cytotoxic drugs

Some alcohols high in purine (e.g. beer contains guanosine)

Metabolism of alcohol produces acetyl CoA which leads to adenine nucleotide degradation –> increased adenosine monophosphate (precursor of uric acid)

Alcohol also leads to increased blood lactate which prevents uric acid secretion

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What sort of inborn errors of metabolism will increased risk of gout?

Rare enzyme defects leading to overproduction of uric acid

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What is HGPRT deficiency?

HGPRT enzyme main function is to salvage purines from degraded DNA to reintroduce into purine synthetic pathways (mostly hypoxanthine & guanine)
Deficiency –> inability to recycle bases –> increased purine degradation –> v. high uric acid levels in blood

(purine synthesis rate accelerated to compensate for failure of salvage process)

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What is an e.g. of HGPRT deficiency?

Lesch-Nayhan syndrome

HGPRT deficiency due to X-linked recessive mutation
Intellectual disability, aggressive and impulsive behaviour, self mutation, gout, renal disease

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What things may cause underexcretion of uric acid?

Renal impairment
Hypertension
Hypothyroidism
Drugs, e.g. alcohol, low dose aspirin, diuretics, cyclosporin
Exercise, starvation, dehydration (inc. lactate)
Lead poisoning

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Who does gout tend to affect?

Older men

Oestrogen as a uricosuric effect (increases uric acid secretion) - so rare in woman until after menopause)

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How common is gout?

Affects 2.5% of adults

What are the risk factors for gout?

DM 
Obesity
High BP and cholesterol
Metabolic syndrome (i.e. things above) 
Alcohol consumption
Diuretic Rx
Dehydration (trigger) 
Ageing

Why are diabetics more at risk of gout?

Decreased ability to excrete uric acid

What causes the majority of gout?

Reduced efficiency of renal urate clearance

What are most gouty attacks triggered by?

RFs

Why is gout more common with age?

Due to decreased renal function, age related changes in connective tissue may encourage crystal formation and increased prevalence of OA

What must you ask in your hx of suspected gout?

Episodic gouty attacks? | RFs?

How do you investigate gout?

Aspirate joint (send for gram stain & culture) Exclude infection Visualise crystals to get definitive diagnosis Check uric acid levels generally unhelpful during attack, but may want to see where they sit at chronically

What sort of crystals do you get in gout?

Needle shaped crystals with negative bifringence

How do you visualise the crystals?

Polarised light microscopy

How do you Rx an acute attack of gout?

NSAIDs Colchicine Steroids (IA (only IM/oral if polyarticular)

When do you Rx hyperuricaemia?

First attack not treated unless single attack of polyarticular gout, tophaceous gout, urate calculi, renal insufficiency Rx second attack within 1y Prophylactically prior to Rx certain malignancies DO NOT RX asymptomatic hyperuricaemia ONCE ATTACK HAS SETTLED

How do you Rx hyperuricaemia?

Allopurinol (1st line, adjust dose according to renal function) Febuxostat Uricosuric agents, e.g. sulphinpyrazone, probenecid, benzbromarone Canakinumab Address RFs (avoid purine rich foods (e.g. shellfish), drinking, wt loss, quiting smoking, better management of BP, stay hydrated etc.)

What is allopurinol?

Xanthine oxidase inhibitors - blocks conversion of xanthine oxidase to hypoxanthine So xanthine not degraded into uric acid

What is pseudogout?

Acute monoarthropathy of larger joints in elderly females due to deposition of calcium pyrophosphate dehydrate

Where do people mostly get pseudogout?

Knee

What is typical in the presentation of pseudogout?

Erratic flares (usually spontaneously, may be triggered by illness, trauma, surgery etc.)

What is the aetiology of pseudogout?

``` Idiopathic - most common Familial metabolic (secondary to hyperparathyroidism, haemachromatosis) ```

What are the types of presentations you can have with pseudogout?

Asymptomatic Acute (pseudogout attack) chronic

How do you diagnose pseudogout?

X-Ray (also to exclude fracture) | Aspirate joint and polarised light microscopy to see crystals

What will you see on Xray with pseudogout?

Chondrocalcinosis (Ca deposits in cartilage of joint)

What type of crystals do you get in pseudogout?

Rhomboid shaped calcium pyrophosphate dihydrate crystals with positive bifringence

How do you Mx pseudogout?

NSAIDs IA steroids after ruling out sepsis NO prophylactic Rx - manage episodes as they come Support joint, rest, analgesia, splinting

What is polymyalgia rheumatica?

Disorder that affects multiple joints and causes pain in surrounding tissues

What is the cause of polymyalgia rheumatic?

Immune mediated | Exact cause not known but assoc. with genetic and environmental factors (?molecular mimicry)

What condition is PR closely associated with?

GCA

In which gender and age group is PR most common?

>70 and 2xF

What is the typical presentation of PR?

``` Symmetrical pain Sudden onset shoulder +/- pelvic girdle STIFFNESS ESR usually >45 Anaemia Malaise, wt loss, fever, depression Arthalgia/synovitis sometimes ``` GCA symptoms

What are the symptoms of GCA?

Headache, pain over temples, jaw claudication, visible temporal artery Can lead to vision loss

How do you diagnose PR?

No specific test Based on Hx & inflame markers raised Question diagnosis if <50 ESR should be >50 Dramatic steroid response (24-48h - 15mg prednisolone) Check for redflags of malignancy/polymyositis

What are your DDx for PR?

``` Myalgic onset inflammatory joint dx Underlying malignancy (MM, lung cancer) Inflammatory muscle dx Hypo/hyperthyroidism Bilateral shoulder capsulitis Fibromyalgia (centralised pain syndrome) ``` CK can differentiate between muscle dx, ensure to check thyroid function

How do you manage PR?

Predisolone 15mg 18-24m Bone prophylaxis - DEXA, if high risk start on Rx (bone loss greatest 3m after starting Rx)

What is calcific periarthritis/tendonitis?

Basic calcium phosphonate hydroxyl-apatite