Crystal Arthropathies

Question 1

What are the common crystal deposition diseases?

Answer 1

Monosodium urate - gout
Calcium pyrophosphate dehydrate - pseudo gout
Basic calcium phosphate hydroxyl-apatite - calcific periarthritis/tendonitis

Question 2

What are crystal deposition diseases characterised by?

Answer 2

Deposition of mineralised material within joints and peri-articular tissue

Question 3

What are the features of gout?

Answer 3

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

Question 4

How do you diagnose gout?

Answer 4

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

Question 5

How long do gout flare ups tend to last?

Answer 5

Flares tend to last 3-10 days and settle spontaneously

Question 6

What joint is most commonly affected by pseudogout?

Answer 6

Knee

Question 7

What are the features of pseudogout?

Answer 7

Typically elderly females - fall/UTI causing admission

Erratic flares

Question 8

What is the aetiology of pseudogout?

Answer 8

Idiopathic
Familial
Metabolic

Question 9

What are the triggers of pseudogout?

Answer 9

Trauma

Intercurrent illness

Question 10

When are x-rays useful in pseudogout?

Answer 10

Useful to exclude trauma and look for chondrocalcinosis but generally not otherwise useful in acute setting

Question 11

What is the management of an acute flare of gout?

Answer 11

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

Question 12

What is the management of pseudogout?

Answer 12

NSAIDs
Intra-articular steroids
No prophylactic therapies

Question 13

Endogenous production of uric acid from degradation of purines usually contributes to how much of the body urate pool?

Answer 13

2/3

The remainder from diet

Question 14

Where is the majority of uric acid that is produced daily excreted?

Answer 14

Via the kidney (about 70%)

The remainder is eliminated into the biliary tract and subsequently converted by colonic bacterial uricase to allantoin

Question 15

In the vast majority of people with gout, hyperuricaemia results from what?

Answer 15

Reduced efficiency of renal urate clearance

Question 16

What are the causes of over-production of uric acid?

Answer 16

Malignancy 
Severe exfoliative psoriasis 
Drugs e.g. ethanol, cytotoxic drugs 
Inborn errors of metabolism
HGPRT deficiency

Question 17

What are the causes of under-excretion of uric acid?

Answer 17

Renal impairment 
Hypertension
Hypothyroidism 
Drugs 
Exercise, starvation, dehydration 
Lead poisoning

Question 18

Why is alcohol thought to increase the risk of gout?

Answer 18

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

Question 19

What are the features of Lesch Nyan Syndrome?

Answer 19

HGPRT deficiency 
X-linked recessive 
Intellectual disability 
Aggressive and impulsive behaviour 
Self-mutilation 
Gout 
Renal disease

Question 20

What is the enzyme defect in Lesch Nyan Syndrome?

Answer 20

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

Question 21

What is the management of hyperuricaemia?

Answer 21

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

Question 22

What is the treatment for lowering uric acid?

Answer 22

Xanthine oxidase inhibitor e.g. allopurinol first line
Febuxostate
Uricosuric agents e.g. sulphinpyrazone
Canakinumab

Question 23

What are the rules for lowering uric acid?

Answer 23

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

Question 24

What is the presentation of polymyalgia rheumatica?

Answer 24

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

Question 25

What are the similarities between polymyalgia rheumatica and giant cell arteritis?

Answer 25

Both characterised by high ESR and anaemia and both affect elderly women

Question 26

How do you diagnose polymyalgia rheumatica?

Answer 26

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

Question 27

What are the differential diagnoses for polymyalgia rheumatica?

Answer 27

Myalgic onset inflammatory joint disease
Underlying malignancy e.g. multiple myeloma
Inflammatory muscle disease
Hypo/hyperthyroidism
Bilateral shoulder capsulitis
Fibromyalgia

Question 28

What is the treatment of polymyalgia rheumatica?

Answer 28

Prednisolone 15mg per day, tapered down slowly over 18-24 month course
Bone prophylaxis