Rheumatology Diagnostics Flashcards
What are diagnostics?
Tests
What are the 3 categories of rheumatology diagnostics?
- Blood tests
- Joint (synovial) fluid analysis
- Imaging tests e.g. X-rays, USS (ultrasounds), CT, MRI
How do you start your investigations with a patient whose PC is painful joints?
- Ask yourself if you even need blood tests - sometimes diagnosis is clear from history and examination alone e.g. osteoarthritis of the knee
- If diagnosis is not achieved from HPC and examination alone, progress to basic blood tests - FBC, U&E, LFTs, Bone profile, ESR, CRP
- Then order ‘fancy’ blood tests e.g. autoantibdies, ANA, etc.
What are the ‘basic’ rheumatology blood tests and what can they each indicate?
FBC = full blood count = can show anaemia, raised WCC, raised platelets indicating inflammatory or septic arthritis
U&E = urea and electrolytes = can show high Cr = worse renal clearance = kidney issue = chronic inflammatory arthritis / long-term use of NSAIDs
LFTs = liver function tests = low albumin - problem of synthesis in the liver or problem of lead in the kidney (e.g. in lupus nephritis)
Bone profile = high ALP from either liver or bone
ESR = erythrocyte sedimentation rate = raised in inflammation except in SLE
CRP = C-reactive protein = more specific for inflammation and normally raised in inflammatory arthritis
What are the different types of arthritis?
Denerative arthritis - e.g. OA, where the cartilage int he joint is worn out
Inflammatory arthritis - e.g. RA, primary problem is the inflammation at the joints
Septic arthritis - infection in the joint and inflammation arises secondary to that
What would the basic blood tests show for inflammatory arthritis?
FBC = Low (anaemia) or normal Hb Normal MCV Usually normal WCC Normal or raised platelet count (PLT)
U&E =
Sometimes elevated Cr
LFTs =
Sometimes low albumin
ESR =
Can be elevated
CRP =
Often elevated
What would the basic blood tests show for osteoarthritis?
FBC = all normal
What would the basic blood tests show for septic arthritis?
FBC = Usually normal Hb Normal MCV Raised WCC (leucocytosis - elevated neutrophils in this is from a bacterial infection) Normal or raised platelet count (PLT)
CRP =
Elevated
What U&E tests are conducted and which one is most important?
Urea
Creatinine (Cr) - most important, suggestive of kidney damage
Sodium
Potassium
Why might Cr levels be elevated in rheumatological diseases and chronic inflammatory diseases?
Cr can be elevated in rheumatological diseases, e.g. in SLE from lupus nephritis
In chronic inflammatory disease e.g. chronic inflammation of blood vessels (vasculitis) can lead to nephritis
Also in chronic inflammatory diseases, there are chronic high levels of SAA (serum amyloid A) protein, which deposits in organs leading to damage to organs (called amyloidosis)
What else can cause an elevated Cr in rheumatology patients, unrelated to the primary pathophysiology of their condition?
Chronic used if NSAIDSs (e.g. ibuprofen) = kidney impairment
What LFTs are conducted?
Bilirubin
Alanine aminotransferase (ALT)
Alkaline phosphatase (ALP)
Albumin
Why is it important to conduct LFTs in rheumatology patients?
DMARDs (disease modifying anti-rheumatid drugs) e.g. methotrexate = liver damage side effect
Patients on methotrexate need regular blood tests every 8 weeks
Why might LFTs turn up with low albumin in rheumatology patients?
Problem of synthesis of albumin in the liver
OR
Problem of leak of albumin from the kidney into the urine (e.g. in lupus nephritis)
What bone profile tests are conducted?
Calcium
Phosphate (PO4-)
Alkaline phosphatase (ALP)
Why is a bone profile conducted?
ALP is sourced from bone and liver, so if the ALP from the LFT comes back raised, we need to figure out whether the liver or the bone is causing this
In what bone conditions can ALP be elevated?
Paget’s disease = abnormal excessive turnover of bone presenting as bone pain, excessive bony growth, and fracture thorugh an area of abnormal bone
Osteomalaia = soft bones due to Vit D deficiency = ALP may be normal or elevated Ca2+ and PO4- are normal or lowered
Osteoporosis = low bone density = normal Ca2+, PO4- and ALP (diagnosis usually made by DEXA scanning - bone density scanning)
What is the purpose of conducting an ESR and CRP?
Both markets of inflammation
CRP more specific marker of inflammation than ESR
What other conditions may cause a raised ESR?
Elevated immunoglobulin level
Paraprotein (myeloma)
Anaemia
Tends to rise with age
In which rheumatology condition is ESR more relevant, and how is this information used to diagnose?
In SLE / lupus =
ESR usually high but CRP normal
EXCEPT
CRP can be high when there is significant synovitis (joint inflammation) or there is an inflammatory pleural or pericardial effusion
If a patient comes in with high CRP, what is the primary suspect?
Infection
What are the ‘fancy’ blood tests for inflammatory arthritis (particularly in RA)?
What do these indicate
Rheumatoid factor (RF) - Antibodies directed against IgG
Cyclin cirtrullinated peptides (CCP) antibodies = more specific -
Positive = suggestive of poorer prognosis i.e. mroe erosion at joint
Anti-nuclear antibodies (ANA) -
High levels of ANA combined with correct clinical features may indicate an autoimmme connective tissue disease
Is RF specific to indicating RA?
No
They can be elevated in the general population
Positive in Hep C
Positive in other autoimmune diseases
Is ANA specific to the rheumatology population?
No
Relatively common in the general healthy population at low levels
Prevelance of ANA increases with age in the egenral population
Sometimes transiently positive following infection
Why is it important to order the ANA test indiscriminately?
It is non-specific
If ordered on everyone with joint pain, there will be many false positives
Therefore only ordered for suspected autoimmune connective tissue disease
What are the different autoimmune connective tissue diseases and how do they manifest?
SLE / lupus = Arthritis Skin rash Mouth ulcers Kidney disease Haematological Pleural effusion Pericardial effusion
Sjogren’s syndrome (some relation to lupus - destruction of the salivary and lacrimal glands)
Dry eyes
Dry mouth
Extra-articular features
Scleroderma =
Vasculopathy (esp. Raynaud’s)
Skin thickening
Organ fibrosis
Polymyositis =
Muscles inflammation
Weakness
High CK (creatinine kinase)
How are ANA tests interpreted?
- ANA test either says negative, or it gives a number
The number refers to ANA presence in maximal dilution:
e.g. 1:80 means ANA still detectable after 80 dilutes (weak), 1:320, 1:640, 1:1280 (strong) - Negative test rules out SLE (lupus)
- BUT positive test does not necessarily mean SLE - but supports diagnosis if present with clinical features
What is conducted next if ANA is positive?
ANA = screening test
Therefore must narrow down which auto-antibody it is causing the positive ANA
So next do ENA (extractable nuclear antigens): a panel of 5 autoantibodies
What does the ENA consist of?
5 autoantibodies - positive in:
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? What is the significance of dsDNA?
Double stranded DNA antibodies
Highly specific for lupus, associated with renal involvement, useful for tracking lupus activity over time
What else is used to monitor lupus?
Complement levels C3 and C4 - tend to go down as the lupus is active
How is a synovial fluid analysis conducted?
- Aspirate joint to get fluid
2. Examine fluid under a microscope
What are the 2 main purposes of a joint aspiration?
- Diagnostic = to obtain synovial fluid for analysis
- Therapeutic = to relief symptomsby taking off the fluid (+/- concurrent steroid injection ONLY if confident there is no infection present)
What are the 2 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
How is synovial fluid analysis conducted for suspected crystal arthritis?
What would the fluid show?
Examined under a microscope using polarised light
Gout = needle shaped crystals with negative birefringence Pseudogout = rhomboid shaped crystals with positive birefringence
What are the key differences in the features of septic arthritis VS reactive arthrtiis?
Septic VS reactive arthritis =
Positive VS sterile synovial fluid
Yes VS no antibiotic therapy treatment
Yes for large joints VS no joint lavage
What are the main imaging modalities in rheumatology and why are they used?
X-rays = first line, cheap, widely available
CT scans = more detailed bony imaging
MRI scans =
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
USS (ultrasounds) =
Like MRI can visualize soft tissue structures.
Good for smaller joints, less good for deep/large joints like knee or hip
Which imaging technique is most useful for OA?
X-rays
What are the X-ray (radiological) features of OA?
Joint space narrowing - bone touching bone
Subchondral bony sclerosis - increased white appearances on the x-ray
Osteophytes - extra bone growths
Subchondral cysts - bone cycts under the cartilage
What imaging technique is most useful for RA?
X-rays
USS (ultrasound scan)
MRI
What are the X-ray (radiological) features of RA?
Soft tissue swelling - can barely been seen on x-rays as they predominantly are limited to view bones
Peri-articular osteopenia
Bony erosions
Ulnar drift of fingers
What is the issue with using X-rays to identify / diagnose RA?
Bony erosions occur only in established disease - the aim of modern therapy is to treat EARLY before erosions (permanent damage) has occurred
Therefore, x-rays are not useful in early rheumatoid and should not be falsely reassured that the patient does not have RA
What are the USS features of RA?
Much better at detecting synovitis changes -
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
USS (usually of hands and wrists) can be performed alongside clinical assessment in a dedicated early arthritis clinic
Why are MRIs used less often?
Often do not provide significantly more info than USS
Time consuming and expensive
What are the differences in the radiographic findings of RA VS OA?
RA VS OA =
Yes VS Yes joint space narrowing No VS Yes subchondral sclerosis No VS Yes osteophytes Yes VS No osteopenia Yes VS No bony erosions
How do RA radiogrpahs differ from osteoarthritis radiographs?
RA =
Erosion and resorption of the distal ulna
Marked erosions at the MCPJs (metacarpophalangeal joints)
Ulnar deviation / ulnar drift of fingers
OA =
MCPJs spared
Clean joints
Changes at DSPJs with increased whitening (sub-controlled sclerosis)
What are the X-ray (radiographic) findings of chronic gout?
X-rays are usually normal during the first few attacks of gout
But over time (many years), radiographs show juxta-articular ‘rat bite’ erosions at the MTPJ of the great toe
What are the radiographic findings of Psoriatic arthritis?
Asymmetry of the joints involved
Sparing of the MCPJs
Involvement / Erosions of the IPJs
Pencil and cup deformities at IPJs
What is the value of an MRI?
X-rays may turn up normal, but symptoms continue to persist, therefore next step is to do an MRI
e.g. 5OF
Acute onset of L hip (groin) pain, no trauma
Constant pain, worsening with weight bearing
PMH of SLE in remission
The hip X-ray turned up completely normal HOWEVER the hip MRI showed reduced and painful internal rotation of the L hip (could progress onto avascular necrosis of the femoral head)
