Crystalline Arthritis

What crystal causes gout?

Monosodium urate (MSU)

What crystal causes pseudogout?

Calcium pyrophosphate dihydrate (CPPD)

What crystal causes Milwaukee shoulder syndrome?

Basic calcium phosphate (BCP)

What is the shape and birefringence of monosodium urate crystals?

Needle-shaped and negatively birefringent

How do Monosodium Urate crystals appear under polarized light when parallel to the compensator?

Yellow (Yellow = Parallel)»Gout»Use aLLupurinol

What is the shape and birefringence of CPPD crystals?

Rhomboid-shaped and positively birefringent

How do CPPD crystals appear under polarized light when parallel to the compensator?

Blue (opposite)

How are basic calcium phosphate crystals identified?

Not seen on polarized microscopy, use scanning EM

What crystal is described as a "shiny coin"?

Basic calcium phosphate crystal

What is the gold standard for diagnosing gout?

Joint aspiration with crystal identification

What is the classic crystal finding in gout?

Negatively birefringent needle-shaped monsodium urate crystals

What is the classic presentation of acute gout?

Acute monoarticular red, hot, swollen, painful joint

What is podagra?

Gout involving the 1st MTP joint

What triggers gout flares?

Changes in uric acid levels, illness, surgery, trauma, alcohol, seafood, red meat, fructose

What are the common causes of hyperuricemia?

Underexcretion of uric acid (renal dysfunction or meds)
Overproduction (Lesch-Nyhan-HGPRT deficiency, Tumor Lysis, Cell turnover increase)

What genetic disorder causes uric acid overproduction and gout?

Lesch-Nyhan syndrome (HGPRT deficiency)

What is first-line treatment for an acute gout flare? Next step in treatment?

Use NSAIDs/indomethacin to stop inflammatory flare(can also use colchicine to abort flare. Then need to lower uric acid for prevention via Allupurinol/febuxostat/Rasburicase

Problem causing gout

High tissue urate level (not serum urate level)>crystals form in the tissue (often at colder temps) causing painful swollen presentation

What is the mechanism of colchicine? ****

Inhibits microtubule assembly, inhibits neutrophil adhesion and chemotaxis, AND blocks activation of NALP3 inflammasome

What are the major adverse effects of colchicine?

Diarrhea, nausea, vomiting, myopathy, bone marrow suppression

What characterizes chronic gout?

Polyarticular disease, incomplete resolution of attacks, tophi

What enzyme is inhibited by allopurinol and febuxostat?

Xanthine oxidase

Which uricosuric drug inhibits URAT1?

Probenecid

Probenecid MOA

Inhibits URAT1 in the proximal tubule resulting in more uric acid excretion

What is a contraindication to probenecid?

Nephrolithiasis (because peeing out more uric acid) and CKD

Why is colchicine often given when starting urate-lowering therapy?

Changes in uric acid can precipitate flares

CPPD (Pseudogout) Arthropathy (Blue P’s, Sx, Imaging, Causes, TX)

Blue P’s: Blue when Parallel, Positive bifringence, calcium Pyrophopshate Pseudogout. Sx: arthritis on knees/wrists; Chondrocalcinosis on imaging

Causes: Inc age, Hyperparathyroidism, Hemochromatosis, )

Tx: NSAIDs, steroids,

Xanthine oxidase inhibitor Allupurinol AE and drug interactions Why?

AE: Hypersensitivity reaction can be deadly. Interacts with Azathioprine/6MP and warfarin

Azathioprine/6MP are converted to inactive metabolites by Xanthine oxidase but if you inhibit it»leads to high concentration of active metabolites

What metabolic diseases are classically associated with CPPD?

Hyperparathyroidism, hemochromatosis, hypomagnesemia, hypothyroidism

What population classically develops Milwaukee shoulder syndrome?

Elderly women

Basic Calcium Phosphate Crystal Deposition (Deposit locations, clinical presentation)

Small non-bifringement crystals depositing in tendons, joints and cartilage. Presents as Milwaukee Shoulder Syndrome, or calcific periarthritis/tendinitis

Milwaukee shoulder syndrome (demographic, presentation, imaging)

Elderly female with dominant shoulder swelling and tenderness; rapid glenohumeral joint destruction and soft tissue calcification and low WBC count in synovial fluid

What crystal is found in Milwaukee shoulder syndrome synovial fluid?

Basic calcium phosphate crystals

What is the key board-style distinction between gout and pseudogout crystals?

Gout = needle-shaped negative birefringence»Yellow Parallel in Gout