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Investigations

X-Rays

RA Hands and feet Jointspace narrowing, erosions
OA   Inter-bone distance
Ank spondy AP pelvis Pseudowidening/blurring of lower 2/3 of SI joint.
Erosion of vertebral end-plates ("squared off").
Psoriatic arthropathy   Asymmetrical small joint erosions (DIP) and periosteal reaction.
Chondrocalcinosis AP knees  
Chronic tophaceous gout   "Punched-out" sclerotic erosions

RA: acute phase

Inflammation results in release of soluble mediators (cytokines, including interleukins 1-6 and TNF) which results in:

Antibodies

Anti nuclear antibody (ANA) +ve in
  • Systemic lupus erythematosus (active) 99%
  • Systemic lupus erythematosus (inactive) 95%
  • Drug induced lupus  99%
  • Mixed connective tissue disease 99%
  • Rheumatoid arthritis 32%
  • Juvenile rheumatoid arthritis 76%
  • Chronic active hepatitis 75% %
  • Sjorgen's syndrome 68%
  • Progressive systemic sclerosis 64%
  • "Normal" controls 0-2% (Increase with age - 20% at 70yrs)
  • Scleroderma 20% (speckled or nuclear staining pattern)
  • Polymyositis and dermatomyositis (80%)
  • CAH, TB, malignancy, old age
  • Speckled: overlap syndromes, CREST.
  • Discoid lupus 25%

More on antinuclear antibodies

Anti-CCP antibodies
  • Better sensitivity and specificity than RF
  • +ve in 50-60% of patients with early RA (within 3-6m of onset of symptoms)
  • 95% of patients with +ve anti-CCP will develop RA in the future
Double stranded DNA (dsDNA) +ve in
Antiphospholipid antibody Associated with venous and arterial thrombosis as well as first trimester abortions. Collagenosis, SLE. Characterised by either its ability to inhibit platelet dependent coagulant reactions (when it is known as lupus anticoagulant) or as an anticardiolipin antibody, detected by its binding in vitro to cardiolipin.
Cardiolipin antibodies +ve in
  • SLE
  • Connective tissue diseases.
Smooth muscle antibody +ve in
  • Chronic active hepatitis 40-90%
  • Primary biliary cirrhosis 30-70%
  • Idiopathic cirrhosis 25-30%
  • Viral infections 80% (low titres)
  • "Normal" controls 3-12%
Gastric parietal cell antibody +ve in
  • Pernicious anaemia (adults) 90-100%
  • Atrophic gastritis:
    • females 60%
    • males 15-20%
  • Autoimmune thyroid disease 33%
  • "Normal" controls 2-16%
Mitochondrial antibody +ve in
  • Primary biliary cirrhosis 60-94%
  • Chronic active hepatitis 25-60%
  • Idiopathic cirrhosis 25-30%
  • "Normal" controls 0.8%
Antibody to reticulin +ve in
  • Coeliac disease 37%
  • Crohn's disease 24%
  • Dermatitis herpetiformis
  • 17-22% "
  • Normal" controls 0-5%
Thyroid antibodies
Microsomal Thryroglobulin
  • Hashimoto's thyroiditis 70-91% 75-95%
  • Grave's disease 50-80% 33-75%
  • Myxoedema 40-65% 50-81%
  • Thyrotoxicosis 37-45% 40-75%
  • Juvenile thyroiditis 91% 72%
  • Pernicious anaemia 55% ?
  • "Normal" controls 10-13% 6-10% (50% in older women)
Rheumatoid factor +ve in
  • Rheumatoid arthritis 70-80%
  • SLE up to 40%
  • Sjorgen's syndrome up to 100%
  • Felty's sndrome up to 100%
  • Progressive systemic sclerosis 30%
  • Still's disease rare
  • Infective endocarditis up to 50%
  • "Normal" controls 5-10%
  • Connective tissue diseases, systemic sclerosis, sjogrens (60%)
  • Cryoglobulinaemia
  • Chronic active hepatitis (CAH)
  • Myeloma (10%)
  • Sarcoid, SBE, TB (40%)
  • Chronic infection
  • Also associated with viral hepatitis, infectious mononucleosis, TB, and leprosy
ANCA (anti-neutrophil cytoplasmic antibody)
  • Wegener's granulomatosis >95% +ve
    (2 types: eANCA against elastase 1, and pANCA against myeloperoxidase. The latter is associated with non-granulomatous small vessel vasculitis. There is a cross-reaction between ANA and pANCA.)
ENA screen  
  Ro (SS-A)
  La (SS-B)
  Sm
  • SLE (30%: associated with membranous nephritis)
  RNP
  • SLE
  • Mixed connective tissue disease
  • Raynauds
  • Myositis
  SCl (PM1)
  • Myositis/scleroderma overlap
  Centromere
  • CREST
  Jo-1 PL7 PL12
  • Myositis and fibrosing alveolitis with raynaud
  • Sicca

Specificity and sensitivity of ANCA serology testing for Wegener's granulomatosis and microscopic polyangiitis (adapted from Hagen et al, Kidney Int 1998;53:743.53)

Specificity of assays (related to disease controls) Specificity/

sensitivity (%)
Indirect immunofluorescence: cANCA  95
pANCA  81
ELISAs: PR3.ANCA  87
MPO.ANCA  91
Combined indirect immunofluorescence and ELISA: cANCA/PR3.ANCA positive  99
pANCA/MPO.ANCA positive  99

 
Sensitivity of combined testing
Wegener's granulomatosis  73
Microscopic polyangiitis  67