Rheumatology Diagnostics Flashcards
What are the different categories in rheumatology diagnostics?
Bloods
Joint (synovial) fluid analysis
Imaging
What blood tests should you order for a patient with painful joints? (Basic)
Full blood count (FBC) Urea and electrolytes (U&E) Liver function tests (LFT) Bone profile Erythrocyte sedimentation rate (ESR) C-reactive protein (CRP)
What should you do before ordering tests?
Do I need these tests?
Can we make a diagnosis on history and examination alone
e.g. osteoarthritis of the knee
What are the three types of arthritis?
Osteo
Inflammatory
Septic
What should be done first when ordering bloods?
Basic tests before ‘fancy’ ones
What are the main components of a FBC?
Hb
MCV
PLT
WCC
What are the Hb readings for different arthritis types?
Inflammatory - low or normal
Osteo - normal
Septic - usually normal
What are the MCV readings for different arthritis types?
All normal
What are the WCC readings for different arthritis types?
Inflammatory - normal
Osteo - normal
Septic - high
What are the PLT readings for different arthritis types?
Inflammatory - normal or high
Osteo - normal
Septic - normal or high
What is looked in U+E’s?
Urea
Creatinine
Sodium
Potassium
What does high Cr indicate?
worse renal clearance (indicating kidney problem)
What is the relevance of Cr in rheumatology?
Rheumatological diseases can affect the kidneys
Give examples of rheumatological diseases that manifest in kidneys?
a) Systemic lupus erythematous (SLE) -> lupus nephritis
b) Vasculitis -> nephritis
c) Chronic inflammation in poorly controlled inflammatory disease
What happens in poorly controlled inflammatory disease?
high levels of serum amyloid A (SAA) protein -> SAA deposits in organs (AA amyloidosis)
How else might rheumatological disease cause kidney malfunction?
Non-steroidal anti-inflammatory drugs (NSAIDs) (eg ibuprofen) can cause kidney impairment
What is looked at in LFTs?
Bilirubin
Alanine aminotransferase (ALT)
Alkaline phosphatase (ALP)
Albumin
What is the relevance of doing 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).
What can low albumin indicate?
can either reflect problem of synthesis (in liver) or problem of leak from kidney (eg in lupus nephritis)
What is done on a bone profile?
Calcium
Phosphate (PO4)
Alkaline phosphatase (ALP)
nb also in LFTs – confusingly the source of ALP can be bone OR liver
In which disease is high ALP seen?
Paget’s disease of bone: ALP ↑↑
Paget’s = disease caused by abnormality of high bone turnover.
What is the bone profile of osteomalacia?
ALP normal or ↑, Ca and PO4 normal or ↓
What is the bone profile of osteoporosis?
usually calcium, PO4 and ALP normal
Aside from inflammation, what can cause a high ESR?
- Elevated immunoglobulin level
- Paraprotein (myeloma)
- Anaemia
- Tends to rise with age
What is usually more specific in inflammation CRP or ESR?
CPR
When would ESR be more useful?
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 the two types of autoantibodies in RA?
Rheumatoid factors
Cyclic citrullinated peptides (CCP) antibodies
Which antibody test is more specific?
Cyclic citrullinated peptides (CCP) antibodies
More specific than RF
Associated with worse prognosis
What is another specialist rheumatology test?
Anti-nuclear antibodies (ANA)
What are the issues regarding the use of ANAs?
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 ANAs 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)
What is important with ANA?
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 are the manifestation of lupus?
Arthritis Skin rash Mouth ulcers Kidney disease Haematological Pleural effusion Pericardial effusion
For which diseases would you order an ANA test?
Lupus
Sjorgen’s
Polymyositis
Scleroderma
How is an ANA test 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 test should be ordered if the ANA comes back positive?
ENA (extractable nuclear antigens): a panel of 5 autoantibodies
What are the 5 antibodies on an ENA panel?
Ro - Lupus or Sjogrens syndrome La - Lupus or Sjogrens syndrome RNP - Lupus or mixed connective tissue disease Smith - Lupus Jo-1- Polymyositis
What is dsDNA?
Double stranded DNA antibodies
What is the significance of dsDNA?
highly specific for lupus, associated with renal involvement, useful for tracking lupus activity over time
What might be low in active lupus?
Complement levels C3 and C4
How is synovial fluid obtained?
By aspiration of the joint
What are the indications for joint aspiration?
a) Diagnostic: to obtain synovial fluid for analysis
b) Therapeutic: to relief symptoms (+/- concurrent steroid injection)
What are the two main diagnostic uses for aspiration?
Suspected septic arthritis Diagnosing crystal arthritis
What are the features of aspiration for septic arthritis?
- gold standard for diagnosis
- send for MC&S
- enables causative organism to be identified
- sensitivities from culture guide antibiotic choice
What are the crystals in gout?
needle shaped crystals with negative birefringence
What are the crystals in pseudogout?
rhomboid shaped crystals with positive birefringence
What are the key features of septic arthritis?
Synovial fluid culture - positive
Antibiotic therapy - yes
Joint lavage - yes for large joints
What are the key features of reactive arthritis?
Synovial fluid culture - sterile
Antibiotic therapy - no
Joint lavage - no
What are the main features of X-rays in Rheum?
first line, cheap, widely available
What are the main features of CT in Rheum?
more detailed bony imaging
What are the main features of MRI in Rheum?
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 main features of USS in Rheum?
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 osteoarthritis?
Joint space narrowing
Subchondral bony sclerosis
Osteophytes
Subchondral cysts
What are the most useful scans in OA?
X-rays
What are the 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
What are the features of USS in RA?
Synovial hypertrophy (thickening) Increased blood flow (seen as doppler signal) May detect erosions not seen on plain X-ray
Why is USS used in RA?
much better test for detecting synovitis
US (usually of hands and wrists) can be performed alongside clinical assessment in a dedicated early arthritis clinic
Joint space narrowing?
Both yes
Subchondral sclerosis?
RA - no
OA - yes
Osteophytes?
RA - no
OA - yes
Osteopenia?
RA- yes
OA- no
Bony erosions?
RA- yes
OA- no
What are the radiographic findings of chronic gout?
X-rays show juxta-articular ‘rat bite’ erosions at the MTPJ of the great toe
What are the radiographic findings of Psoriatic arthritis?
Asymmetry
Sparing of the MCPJs
Erosions of the IPAs