CRYSTAL ARTHROPATHIES & DEGENERATIVE JOINT DISEASE

Gout

•    Cause: deposition of monosodium urate crystals in joints (hyperuricaemia)

•    Crystals:

o    Needle-shaped

o    Negatively birefringent under polarised light

•    Typical presentation:

o    Sudden onset monoarthritis (e.g. 1st MTP — podagra)

o    Erythema, severe pain, swelling

•    Risk factors:

o    Male, obesity, alcohol, thiazides, CKD, high-purine diet

•    Tests:

o    Serum uric acid (can be normal in acute attack)

o    Joint aspiration: diagnostic (rule out septic arthritis)

o    U&E (check for CKD), consider urate crystals in tophi

•    Management:

o    Acute:

    NSAIDs (first-line if no contraindications)

    Colchicine (GI side effects common)

    Steroids (oral or intra-articular)

o    Chronic (urate lowering therapy):

    Allopurinol (xanthine oxidase inhibitor) – start 2 weeks after flare settles

    Febuxostat (if allopurinol not tolerated)

    Aim for serum urate <360 µmol/L

    Co-prescribe colchicine 500 mcg OD–BD for flare prophylaxis when initiating urate-lowering therapy

Calcium Pyrophosphate Deposition Disease (CPPD / Pseudogout)

•    Crystals:

o    Rhomboid-shaped

o    Positively birefringent

•    Typical joints:

o    Knee, wrist, shoulder

•    Radiology:

o    Chondrocalcinosis (calcification of cartilage) on X-ray

•    Associated conditions:

o    Haemochromatosis

o    Hyperparathyroidism

o    Hypomagnesaemia

o    Hypothyroidism

•    Management: similar to gout

o    NSAIDs, colchicine, steroids

o    No long-term urate-lowering therapy

Osteoarthritis (OA)

•    Features:

o    Affects weight-bearing joints: knees, hips, spine

o    Also affects DIPs, PIPs, 1st CMC (unlike RA)

o    Morning stiffness <30 minutes, worsens with use

•    Signs:

o    Heberden’s nodes (DIP)

o    Bouchard’s nodes (PIP)

o    Joint crepitus, reduced range of motion

•    X-ray findings:

o    Joint space narrowing

o    Subchondral sclerosis

o    Osteophytes

o    Subchondral cysts

•    Management:

o    Non-pharmacological: weight loss, exercise, physio

o    Pharmacological: paracetamol ± topical NSAIDs → oral NSAIDs ± PPI → intra-articular steroids

o    Consider surgery if severe (e.g. joint replacement)

Basic Calcium Phosphate (BCP) Deposition

•    Includes hydroxyapatite deposition disease

•    Not birefringent, not seen on standard microscopy

•    Requires electron microscopy or special stains for identification

•    Presentation:

o    Often affects shoulder (“Milwaukee shoulder”)

o    May cause destructive arthropathy, effusions

•    Treatment: conservative, NSAIDs, physiotherapy; joint lavage in severe cases