Monoarthritis

Today we discussed acute monoarthritis. Some points about the general approach and specific causes:

First question: Is this really arthritis (i.e. is it articular)? Important because non-articular causes are completely different (edema, ligamentous, tendon injury, etc)

Articular: Pain with any range of motion, effusion, morning stiffness, jt line tenderness. If multiple areas involved, more likely articular
Non-articular: Pain with specific ranges of motion, none of above.

Common causes of acute mono or pauciarthritis:
Septic arthritis- S. aureus, N. gonorrhea, S. pneumo
Crystal- gout/CPPD
Seronegative arthritis- esp. reactive, IBD-associated
RA (mono-articular)
Sarcoidosis (often bilateral ankle)
Trauma (fracture, hemarthrosis)

Common causes of acute polyarticular arthritis:
Endocarditis
Viral (HBV, HIV, parvo)
Serum sickness (drug rxn)
RA
SLE
Lyme (may also be monoarticular)

Some general features of specific causes:

Septic arthritis:
Risk factors: age, diabetes mellitus, rheumatoid arthritis, joint surgery, hip or knee prosthesis, skin infection, HIV, IV drug use
Clinical features: Joint pain in ~85%, joint welling in ~80%, and fever in ~60%
There are no physical exam findings that reliably rule in or out septic arthritis according JAMA Rational Clinical Exam paper linked below
Joint aspirate:
WBC over 100,000- Positive LR 28
WBC over 25,000- Positive LR 2.9
WBC less than 25,000- Negative LR 0.32
PMN over 90%- Positive LR 3.4; Negative LR 0.34
Also send for Gram stain, C+S, crystals
Common organisms:
St. aureus, St. pneumo, N. gonorrheae, Gram neg bacilli
Empiric tx: vancomycin and ceftriaxone

Crystal arthritis:
NB- finding crystals does not rule out septic joint! Can present the same way with fever, high WBC.
Gout vs pseudogout:
Gout: needle-like crystals, negatively birefringent, 1st MTP/ankle/knee. Risk factors are hyperuricemia, obesity, culprit meds (HCTZ, low dose ASA, others)
CPPD: rhomboid crystals inside macrophages, often hemorrhagic synovial fluid, positively birefringent. Knee, wrist, other. Risk factors: hypercalcemia, hemochromatosis, CKD.

Gout therapy
Acutely: Options are NSAID/colchicine/intra-articular steroid/systemic steroid
NSAID: Not in CHF or renal failure
Colchicine: Works, but often limited by GI side effects
Steroid:
Intra-articular highly effective with 1-2 jts. Confirm the diagnosis first.
Systemic- Prednisone 30-50mg PO x 3-5d then stop. Works well, but side effects.

Chronically: if 3 or more attacks per years, consider allopurinol

Links:
Click here for CMAJ review of monoarthritis
Click here for JAMA: Does this Patient have Septic Arthritis?