Lupus Autoantibodies
ANA (> 95% sensitive, screening); Anti-dsDNA (specific, correlates with lupus nephritis & disease activity); Anti-Smith (most specific).
Rheumatoid Arthritis
Symmetric polyarthritis of MCP and PIP joints (spares DIPs); morning stiffness > 1 hr; Anti-CCP antibody (most specific).
Gout Crystals
Monosodium urate; needle-shaped, negatively birefringent (yellow under parallel polarized light); acute therapy: Indomethacin / Colchicine / Steroids.
Pseudogout (CPPD)
Calcium pyrophosphate; rhomboid-shaped, positively birefringent (blue under parallel light); chondrocalcinosis on knee X-ray.
Comprehensive Rheumatology Autoantibody Master Table
| Antibody | Associated Disease | Clinical & Board Significance |
|---|---|---|
| Anti-dsDNA | Systemic Lupus Erythematosus (SLE) | High specificity; titers fluctuate with disease activity and renal involvement (Lupus Nephritis) |
| Anti-Smith (Sm) | Systemic Lupus Erythematosus (SLE) | Most specific antibody for SLE; does not correlate with disease activity |
| Anti-Histone | Drug-Induced Lupus (DILE) | Positive in > 95% of DILE (Hydralazine, Procainamide, Isoniazid, Minocycline) |
| Anti-CCP (ACPA) | Rheumatoid Arthritis | Highest specificity (> 95%); predicts aggressive, erosive disease course |
| Anti-Ro (SSA) / Anti-La (SSB) | Sjögren Syndrome & Neonatal Lupus | Risk of Congenital Complete Heart Block in neonates born to SSA+ mothers |
| Anti-Centromere | Limited Cutaneous Systemic Sclerosis (CREST) | Calcinosis, Raynaud, Esophageal dysmotility, Sclerodactyly, Telangiectasia |
| Anti-Scl-70 (Topoisomerase I) | Diffuse Cutaneous Systemic Sclerosis | Extensive skin thickening, high risk of Pulmonary Interstitial Fibrosis and Renal Crisis |
| Anti-Jo-1 (Histidyl-tRNA synthetase) | Polymyositis / Dermatomyositis | Associated with interstitial lung disease and 'mechanic's hands' |
Synovial Fluid Analysis & Crystal Arthropathies
Arthrocentesis is mandatory in any acute monoarthritis to distinguish crystal-induced disease from infectious septic arthritis:
| Condition | WBC Count (/ μL) | Crystal Morphology | Birefringence Under Polarized Light |
|---|---|---|---|
| Gout | 2,000 – 50,000 (> 50% PMNs) | Needle-shaped monosodium urate | Negatively birefringent (Yellow when parallel to compensator) |
| Pseudogout (CPPD) | 2,000 – 50,000 (> 50% PMNs) | Rhomboid-shaped calcium pyrophosphate | Positively birefringent (Blue when parallel to compensator) |
| Septic Arthritis | > 50,000 (often > 100,000; > 75-90% PMNs) | No crystals (unless coexisting) | Gram stain positive in 50-75% of staphylococcal infections |
OMM Board Correlate: Cervical Spine Safety in Rheumatoid Arthritis
- Atlantoaxial (AA) Instability: Rheumatoid pannus formation targets the synovial bursa surrounding the odontoid process (dens), leading to laxity or erosion of the transverse ligament of the atlas.
- Absolute Contraindication: High-Velocity Low-Amplitude (HVLA) thrusting to the cervical spine is strictly contraindicated in patients with Rheumatoid Arthritis or Down syndrome due to the risk of dens dislocation and fatal brainstem / spinal cord compression.
- Safe Modalities: Indirect techniques such as Counterstrain and gentle Myofascial Release are safe and effective for periarticular tension.
Board Traps & Common Distractors
- Any acutely hot, swollen, erythematous monoarticular joint must undergo emergent arthrocentesis to rule out septic arthritis; never start intra-articular steroids before excluding infection.
- In patients with Rheumatoid Arthritis undergoing elective surgery, flexion and extension cervical spine radiographs are mandatory prior to intubation to assess for occult AA subluxation.
- Do not initiate allopurinol or febuxostat during an acute gout flare; rapid shifts in serum uric acid worsen joint inflammation. Continue existing urate-lowering therapy if already taking it, but initiate acute anti-inflammatory agents first.