Rheumatological Diagnostics Flashcards
What are the basic Rheumatology blood tests?
Full blood count (FBC) Urea and electrolytes (U&E) Liver function tests (LFT) Bone profile Erythrocyte sedimentation rate (ESR) C-reactive protein (CRP)
What are the blood results for Inflammatory arthritis?
Low Hb (anaemia) or normal
Normal MCV
Normal WCC
Normal/raised PLT
What are the blood results for Osteoarthritis?
Normal;
Hb, WCC, MCV, PLT
What are the blood results for Septic arthritis?
Normal Hb, MCV
Raised WCC - Leukocytosis
Normal/raised PLT
What do Urea & electrolytes show?
Urea (U)
Creatinine (Cr)
Sodium
Potassium
Higher Cr = worse renal clearance (indicating kidney problem)
What is the relevance of Urea & electrolyte test?
Rheumatological diseases can affect the kidneys
Examples:
a) Systemic lupus erythematous (SLE) -> lupus nephritis
b) Vasculitis -> nephritis
c) Chronic inflammation in poorly controlled inflammatory disease
-> high levels of serum amyloid A (SAA) protein -> SAA deposits in organs (AA amyloidosis)
Non-steroidal anti-inflammatory drugs (NSAIDs) (eg ibuprofen) can cause kidney impairment
What is measured in Liver function tests LFTs?
Bilirubin
Alanine aminotransferase (ALT)
Alkaline phosphatase (ALP)
Albumin
What is the relevance of LFTs?
Disease modifying anti-rheumatic drugs (DMARDs) (eg methotrexate) can cause liver damage.
Key point: patients on methotrexate need regular blood tests (eg every 8 weeks).
Low Albumin: can either reflect problem of synthesis (in liver) or problem of leak from kidney (eg in lupus nephritis)
What is shown in a bone profile?
Calcium
Phosphate (PO4)
Alkaline phosphatase (ALP)
nb also in LFTs – confusingly the source of ALP can be bone OR liver
What can a bone profile show?
Paget’s disease of bone: ALP ↑↑
Paget’s = disease caused by abnormality of high bone turnover.
Clinical features: bone pain, excessive pain growth, fracture through area of abnormal bone
Osteomalacia (soft bones due to vitamin D deficiency): ALP normal or ↑, Ca and PO4 normal or ↓
Osteoporosis (low bone density): usually calcium, PO4 and ALP normal
What do ESR & CRP show?
Both ESR and CRP are useful markers of inflammation
However, ESR can be up for other reasons:
- Elevated immunoglobulin level
- Paraprotein (myeloma)
- Anaemia
- Tends to rise with age
Usually CRP is more specific for inflammation
What is the rule of thumb in SLE?
ESR usually high but CRP normal
Exceptions to the rule: CRP high in SLE if there is significant synovitis or there is an inflammatory pleural or pericardial effusion
If CRP in lupus, have a low index of suspicion for infection
What are Anti-nuclear antibodies?
Antibodies directed at nuclear component of the cell
Non-specific:
Relatively common in general healthy population at low titre (level)
Prevalence of ANA increases with age in the general population
Sometimes transiently positive following infection
What is the use of ANA in Rheumatology?
High titre ANA in combination with the correct clinical features may indicate one of the autoimmune connective tissue diseases (eg SLE, Sjogren’s syndrome, scleroderma)
Learning point: important to order this test judiciously. If you order it indiscriminately you will cause many healthy people to have an abnormal test result which will lead to anxiety and unnecessary referral to hospital and further investigation. Only order if you suspect autoimmune connective tissue disease clinically
What is the presentation of Sjorgen’s syndrome?
Dry eyes
Dry mouth
Extra-articular features
What is the presentation of SLE?
Arthritis Skin rash Mouth ulcers Kidney disease Haematological Pleural effusion Pericardial effusion
What is the presentation of Scleroderma?
Vasculopathy (esp. Raynaud’s phenomenon)
Skin thickening
Organ fibrosis
What is the presentation of Polymyositis?
Muscle inflammation
Weakness
High CK
How do you interpret ANA?
- Strength of ANA is reported as maximal dilution at which it is still detectable
eg 1:80 (weak), 1:320, 1:640, 1:1280 (strong) - Negative test rules out SLE
- Positive test does not necessarily mean SLE, but suggestive IF there are other clinical and lab features to support the diagnosis. A stronger test is more likely to be clinically significant
What should you do if ANA is positive?
If ANA is positive, other tests to order
ENA (extractable nuclear antigens): a panel of 5 autoantibodies
Ro Lupus or Sjogrens syndrome
La Lupus or Sjogrens syndrome
RNP Lupus or mixed connective tissue disease
Smith Lupus
Jo-1 Polymyositis
Double stranded (dsDNA) antibodies: highly specific for lupus, associated with renal involvement, useful for tracking lupus activity over time Complement levels C3 and C4: may be ↓ in active lupus
What are the diagnostic indications for joint aspiration?
a) Diagnostic: to obtain synovial fluid for analysis
b) Therapeutic: to relief symptoms (+/- concurrent steroid injection)
What are the main diagnostic uses for aspiration?
- Suspected septic arthritis
- gold standard for diagnosis
- send for MC&S
- enables causative organism to be identified
- sensitivities from culture guide antibiotic choice
- Diagnosing crystal arthritis
What is different for treatment of reactive arthritis compared to septic arthritis?
sterile synovial fluid culture
no antibiotic therapy
no joint lavage
What imaging tests are done in rheumatology?
X-rays: first line, cheap, widely available
CT scans: more detailed bony imaging
MRI:
Best visualization of soft tissue structures like tendons and ligaments
Best for spinal imaging: can see spinal cord and exiting nerve roots
Expensive and time-consuming
Ultrasound:
Like MRI can visualize soft tissue structures.
Good for smaller joints, less good for deep/large joints like knee or hip
What are the radiographic features of OA?
Joint space narrowing
Subchondral bony sclerosis
Osteophytes
Subchondral cysts
What are the X-ray features of RA?
Joint space narrowing Osteopenia Soft tissue swelling Peri-articular osteopenia Bony erosions
NB erosions occur only in established disease. The aim of modern therapy is to treat EARLY before erosions (permanent damage) has occurred
What are the US features of RA?
Ultrasound (US) is a much better test for detecting synovitis. US changes in RA: Synovial hypertrophy (thickening) Increased blood flow (seen as doppler signal) May detect erosions not seen on plain X-ray
US (usually of hands and wrists) can be performed alongside clinical assessment in a dedicated early arthritis clinic
Would you use MRI for RA?
you can but its expensive/time-consuming
