Rheumatology Diagnostics Flashcards
What are rheumatology diagnostic options?
Blood tests, Synovial fluid analysis, Imaging tests (X-ray, MRI, CT, ultrasound)
What are the general principles of ordering blood tests?
1) Is it required - diagnosis may be clear from history and examination
2) Start with basic blood tests
What is a basic blood test?
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 major divisions of arthritis?
Osteoarthritis (degenerative arthritis)
Inflammatory arthritis (main type being rheumatoid arthritis)
Septic arthritis
What is measured in FBC and what does it indicate?
Inflammatory arthritis - low haemoglobin (anaemia) or can be normal, normal MCV, normal WCC, normal or raised platelet count
Osteoarthritis - normal FBC
Septic arthritis - usually normal haemoglobin, normal MCV, raised WCC due to neutrophils (leucocytosis), normal or raised platelet count.
What is measured in urea and electrolytes test?
Urea (U)
Creatinine (Cr)
Sodium
Potassium
Higher Cr = worse renal clearance (indicating kidney problem)
Why is urea and electrolytes test relevant?
Rheumatological diseases can affect the kidneys
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 an LFT?
Bilirubin
Alanine aminotransferase (ALT)
Alkaline phosphatase (ALP)
Albumin
Why is an LFT relevant?
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 does a bone profile take into account?
Calcium
Phosphate (PO4)
Alkaline phosphatase (ALP) - also in LFTs – the source of ALP can be bone OR liver
Why is a bone profile relevant?
- Paget’s disease of bone: raised 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 raised, Ca and PO4 normal or decreased in very severe cases
- Osteoporosis (low bone density): usually calcium, PO4 and ALP normal
Why are ESR and CRP useful?
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 a 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 low in lupus, have a low index of suspicion for infection
What autoantibodies are found in rheumatoid arthritis?
1) Rheumatoid factor (RF) - Antibodies that recognize the Fc portion of IgG as their target antigen typically IgM antibodies i.e. IgM anti-IgG antibody. Positive in 70% at disease onset and further 10-15% become positive over the first 2 years of diagnosis.
2) Cyclic citrullinated peptides (CCP) antibodies - More specific than RF and associated with worse prognosis
What are the non-specific indications of ANA?
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).
Why should ANA be ordered 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 are features of SLE?
Arthritis Skin rash Mouth ulcers Kidney disease Haematological Pleural effusion Pericardial effusion
PASH KPM
What are features of Sjorgen’s syndrome?
Dry eyes
Dry mouth
Extra-articular features
What are features of polymyositis?
Muscle inflammation
Weakness
High CK
What are features of scleroderma?
Vasculopathy (esp. Raynaud’s phenomenon)
Skin thickening
Organ fibrosis
How is ANA result interpreted?
- 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 other tests should be ordered if ANA is positive?
- 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 low in active lupus
What is the purpose of joint aspiration and what are the two main diagnostic uses for aspiration?
Purpose:
a) Diagnostic: to obtain synovial fluid for analysis
b) Therapeutic: to relief symptoms (+/- concurrent steroid injection)
Diagnostic uses:
- 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 are the microscopic findings for crystal arthritis?
The diagnosis of crystal arthritis is made by aspirating fluid from the affected joint and examining it under a microscope using polarized light.
Gout: needle shaped crystals with negative birefringence
Pseudogout: rhomboid shaped crystals with positive birefringence
What are the key differences between septic arthritis and reactive arthritis?
Synovial fluid culture positive for septic arthritis but sterile for reactive arthritis. Antibiotic therapy required for septic arthritis but not for reactive arthritis. Joint lavage needed in septic arthritis in large joints but not required for reactive arthritis.
What are the pros and cons of X-rays and MRIs?
X-rays: first line, cheap, widely available
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
What are the pros and cons of CT scans and ultrasound?
CT scans: more detailed bony imaging
Ultrasound:
Like MRI can visualize soft tissue structures.
Good for smaller joints, less good for deep/large joints like knee or hip
What are radiographic features of osteoarthritis?
Joint space narrowing
Subchondral bony sclerosis
Osteophytes
Subchondral cysts
What radiographic information do X-rays provide about rheumatoid arthritis?
Radiographic features of RA:
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
Information from X-rays is limited to bony structures
What radiographic information does ultrasound provide about rheumatoid arthritis?
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.
Compare radiographic changes in osteoarthritis in rheumatoid arthritis?
- Joint space narrowing occurs in both due to articular cartilage loss. This can occur in osteoarthritis (primary abnormality) and in Rheumatoid Arthritis (secondary damage due to synovitis).
- Subchondral sclerosis occurs in osteoarthritis but not rheumatoid arthritis.
- Osteophytes occur in osteoarthritis but not rheumatoid arthritis. Osteophytes at the distal inter-phalangeal joints are termed Heberden’s nodes, those at the proximal inter-phalangeal joints are called Bouchard’s nodes.
- Osteopenia occurs in rheumatoid arthritis but not osteoarthritis. Juxta-articular osteopenia is common early radiographic sign in inflammatory arthritis of any cause.
- Bony erosions common in RA but not OA. erosions occur initially at the margins of the joint where the synovium is in direct contact with bone.
What are radiographic features of gout?
X-rays show juxta-articular ‘rat bite’ erosions at the MTPJ of the great toe
What are radiographic features of psoriatic arthritis?
Asymmetrical pattern of joint involvement, erosions of interphalangeal joints, MCPJs not affected
