rheum diagnostics Flashcards
What blood tests do you do in rheumatology?
Full blood count FBC, urea & electrolytes (U & E), liver function tests (LFT), bone profile, erythrocyte sedimentation rate (ESR), C-reactive protein CRP
What is seen on FBC of inflammatory arthritis?
Low Hb (anaemia) or normal, MCV normal, WCC usually normal, platelet normal or increased
What is seen on FBC of osteoarthritis?
all normal
What is seen on FBC of septic arthritis?
Hb usually normal (acute), MCV normal, WCC increased (neutrophilic leucocytosis), platelet count normal or high if marked inflammation
What molecules are involved In urea & electrolytes? What can affect these?
- Urea, creatinine, sodium, potassium.
- High creatinine indicates renal problem.
- Rheum diseases can affect kidneys eg. SLE lupus nephritis, vasculitis to nephritis, chronic inflammation leads to high levels of Amyloid A (SAA) protein, deposition in organs leads to organ damage AA amyloidosis.
- NSAIDs can cause kidney problems
What molecules are involved in LFT? When can these be deranged?
- Bilirubin, alanine aminotransferase (ALT), alkanine phosphatase ALP, albumin.
- DMARDs can cause liver damage (methotrexate need regular blood tests every 8wks).
- Low albumin can reflect liver or renal problems (increased leak in lupus nephritis).
What is included in the bone profile? When can these be deranged?
- Calcium, phosphate, alkaline phosphatase ALP.
- Paget’s disease of bone causes high ALP because abnormal bone turnover (bone pain, growth pain, fractures.
- Osteomalacia (soft bones vitamin D deficiency): ALP normal or high, Calcium & phosphate normal or low.
- Osteoporosis (low bone density): normal
What are ESR & CRP markers of? When are they deranged?
- Inflammation.
- ESR can be raised for other reasons eg. Elevated immunoglobulin levels, paraprotein (myeloma), anaemia, age.
- CRP more specific for inflammation.
- In SLE ESR more useful (ESR usually high but CRP normal), CRP only high in SLE if significant synovitis or inflammatory pleural or pericardial effusion.
- Low index for infection suspicion
What antibodies are present in RA?
- Rheumatoid factor (not specific for RA, can be in hep C or generally).
- Anti-CCP antibodies: more specific than RF - associated with worse prognosis of RA
What are anti-nuclear antibodies ANA? When is it deranged? When do you order it?
- Antibodies against nuclear component of cell.
- Non-specific, can be in healthy population in low level and increases with age, sometimes transiently after infection.
- High level ANA + correct clinical findings can point to autoimmune inflammatory diseases (SLE, sjorgen’s syndrome, scleroderma).
- Only order if suspect it because can lead to anxiety as is non-specific
What are symptoms of SLE? FBC?
- Arthritis, skin rash, mouth ulcers, kidney disease, haematological, pleural effusion, pericardial effusion.
- Low lymphocytes and platelets
What are symptoms of sjorgen’s syndrome?
Dry eyes, dry mouth due to destruction of salivary and lacrimal glands, extra-articular features
What are symptoms of scleroderma?
Vasculopathy - raynauds, skin thickening, organ fibrosis
What are symptoms of polymyositis?
Muscle inflammation, weakness, high creatine kinase
What do you do if you suspect autoimmune connective tissue diseases? What diseases are included?
Order ANA.
-Includes SLE, sjorgens syndrome, scleroderma, polymyositis
How is ANA interpreted? What does a negative & a positive test mean? What do you do if its is positive?
- Reported as maximal dilution at which still detectable eg. 1:80 weak, 1:1280 strong.
- Negative test rules out SLE but positive test doesn’t mean SLE, but suggestive with right clinical & lab features.
- If positive order other tests ENA (extractable nuclear antigens - panel of 5 antibodies)
What is included in ENA (extractable nuclear antigens)?
Panel of 5 antibodies.
Ro (lupus & sjorgens), La (lupus & sjorgens), RNP (lupus or mixed connective tissue diseases), smith (lupus), jo-1 (polymyositis)
What do dsDNA antibodies do? What are they associated with? Uses?
Antibodies against doubles stranded DNA, highly specific for lupus. Associated with renal involvement. Good for tracking lupus activity over time
What happens to complement levels in lupus?
Low complement levels C3 & C4 in active lupus
What is synovial fluid analysis? What are indications for it?
Aspirate fluid from joint. Diagnostic (for analysis) or therapeutic (relief or symptoms +/- concurrent steroid injection)
- suspected septic arthritis (gold standard, send for culture/gram stain + sensitivities)
- diagnose crystal arthritis
What is seen in gout in synovial fluid analysis?
Under polarised light with microscope see needle shaped crystals negative birefringence
What is seen in pseudogout in synovial fluid analysis?
under polarised light with microscope see rhomboid shaped crystals with positive birefringence
What is seen in synovial fluid analysis for septic arthritis? What do you do?
Culture positive. Antibiotics + joint lavage
What is seen in synovial fluid analysis for reactive arthritis? What do you do?
Synovial fluid sterile. No antibiotics or joint lavage
What is 1st line imaging used in rheumatology and why?
X rays. Cheap, available
What do CT scans offer?
more detailed bone imaging
What do MRI scans offer? When are they best? disadvantages?
Best visualisation for soft tissue (tendons/ligaments).
Best for spinal imaging (cord & nerve roots).
Expensive & time consuming
When is ultrasound best used?
Soft tissue. Good for smaller joints, less good for large/deep joints (knee/hip)
What are x-ray features of osteoarthritis?
Joint space narrowing, osteophytes (bone spurs), subchondral cysts (bone cysts under cartilage), subchondral bony sclerosis (increased whitening)
What do we see in imaging of RA? What imaging is used?
- X-ray: Soft tissue swelling, peri-articular osteopenia, bony erosions (only in established disease - treat before permanent damage), joint space narrowing.
- ultrasound - better for detecting synovitis. Synovial hypertrophy, increased blood flow seen as doppler signal, maybe erosions not seen in x-ray. Hands/wrists + clinical assessment for early RA
- MRI - yes but expensive/time consuming
What is seen in gout x-ray?
Juxta-articular rat bite erosions at MPTJ of toe
What is seen in psoriatic x-ray?
Asymmetry, sparing of MCPJ but involvement of intraphalangeal joints
Why can MRI be used for femoral head?
Avascular necrosis - bone infarction due to impaired blood supply
