Rheumatology: diagnostics and tests Flashcards
What are diagnostics?
Rheumatology diagnostics is divided into 3 categories
In terms of imaging X-ray is the main one
Learning objectives:
Be able to:
- List the main diagnostics used in the diagnosis of rheumatological diseases
- Understand which tests to order in common clinical scenarios
- Interpret the results of diagnostic tests, either in isolation or in combination with other tests and clinical information
- Be able to describe the difference in the x-ray findings of osteoarthritis versus rheumatoid arthritis
Part 1: blood tests in rheumatology
-most value comes from history eg patient with painful knee when they walk that gets better when they rest- you then examine and there is boney swelling in the knee, with no effusion and there is crepitus, you can confidently conclude that they have osteoarthritis of the knee, and probs don’t need further tests unless person is having surgery and then you might get an x-ray.
Basic blood tests before fancy autoantibody tests
‘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)
think you need a ‘FULBEC’
Types of arthritis – a reminder
OA/degenerative arthritis-where cartilage is worn out (this is not an inflammatory disease)
Inflammatory arthritis and main problem is inflammation, usually caused by autoimmune disease.
Septic arthritis-there is an infection in the joint and inflammation arises secondary to that.
‘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)
Full blood count (FBC):
(known in America as complete blood count or CBC)
-Anaemia can pccur in inflammatory arthritis, if the patient has long standing uncontrolled inflammation, it can suppress the bone marrow, so less production of red cells, so there is anaemia. However this isn’t always present and sometime the Hb may be normal.
When there is anaemia, it tends to be a normocytic anaemia, that is to say that the MCV is normal.
In contrast in OA where there is no inflammation, the Hb will be normal
In septic arthritis also, because it’s an acute problem, usually the Hb will be normal and hasn’t had time to drop becuase there hasn’t been chronic inflammation yet. There will be a elevated white cell count-leukocytosis, and usually if look at breakdown of white blood cell numbers, this elevation is usually due to neutrophils, and this is classic of bacterial infection.
platelet- reactive increase can be seen if there is chronic or marked inflammation
Urea and electrolytes (U&E)
With this we get back:
- Urea (U)
- Creatinine (Cr)- we are most interested in this
- Sodium
- Potassium
Relevance to rehumatology is that Rheumatological diseases can eb multisystem diseases, affecting multiple organs apart from the joints, and the kidneys is one of these organs
Shown on slide are examples of Rheumatological diseases that may affect the kidneys eg SLE which can cause lupus nephritis which is a kidney infection, vasculitis can lead to a form of nephritis known as glomerular nephritis, and thirdly, in patients with chronic inflammatory diseases, if they are not well treated and their inflammation is not well controlled, there can be chronic high levels of serum amyloid A protein. SAA is produced in the liver as part of the acute phase response to inflammation, and if it is chronically elevated it can deposit overtime in organs leading to damage to the organ, and this is what we call amyloidosis, because of the nature of what these proteins looks like when they are deposited-they form structures called amyloid. You don’t see this so much nowadays because of modern rheumatological treatment, eg with anti-TNF therapy, it is much better than historical treatment, but there are still some patients who’ve had a poorly controlled disease for one reason or another for many years, where they present late with say renal failure, due to amyloid deposition in the kidney.
The other reason why we care about the U and E in rheumatology is that NSAIDs like ibuprofen, when used log term can cause kidney damage and so the kidney function might be impaired as a side effect of the treatment.
Liver function tests (LFTs)
Here we get 4 readings:
- Bilirubin
- Alanine aminotransferase (ALT)
- Alkaline phosphatase (ALP)
- Albumin
Patients taking methotrexate eg for RA, need regular blood tests, usually every 8 weeks.
Albumin is recorded on LFT because it is made in the liver, so a low albumin level can reflect a liver problem ie the liver is not making enough albumin, however this can also occur if there is excessive leak of albumin from the circulation via the kidneys. So in lupus nephritis when the kidneys are inflammed, you can leak albumin from the blood into the urine, and that can cause a low albumin.
Bone profile
Tests:
- Calcium
- Phosphate (PO4)
- Alkaline phosphatase (ALP)
note ALP is also in LFTs – confusingly the source of ALP can be bone OR liver. So remember a high ALP could be due to a boney problem eg Paget’s disease!
Diagnosis of osteoporosis is generally done through DEXA scanning and looking where the person’s bone density sits in relation to the population at their age etc.
ESR and CRP
ESR can be elevated for reasons other than inflammation
Elderly people may have a ESR higher than normal
CRP is our main marker that inflammation is present, whereas there could be other reasons for a high ESR.
However there is one scenario where the ESR is probably more useful than the CRP, and that is in Lupus, or SLE. Here ESR is high and CRP is normal.
Exception to this rule-CRP can be high where there is significant synovitis, so joint inflammation. Or when there’s an inflammatory pleural or pericardial effusion.
If patient comes in with high CRP, you should always suspect infection as the first thing
Autoantibodies in rheumatoid arthritis
ESR and CRP are good screening tests, but if they are both negative and there are not clear clinical signs of inflammatory arthritis, then it’s likely that the patient doesn’t have inflammatory arthritis. However if the ESR and CRP are elevated, and/or there is clear evidence of inflamatory arthritis, so prolonged morning stiffness or overt swelling on joint examination, then you might want to go on and do some of the more specialist rheumatology tests. An example of these would be the antibodies seen in RA.
Rheumatoid factors are not completely specific for rheumatoid arthritis, so they can be up in healthy population, they can also be postive in patients with hepatitis C infection, and also in other autoimmune diseases like sjogren’s syndrome.
A more specific test for RA is the anti-CCP antibody test. Presence of anti-CCP is associated with worse prognosis, so more progressive disease, more likely to cause erosions etc.
Anti-nuclear antibodies (ANA)
Lots of flase positives in healthy people, so only order ANA if clinically suspect autoimmune connective tissue disease
The autoimmune connective tissue diseases
Lupus-presents with joint pain, arthritis, sometimes pain without clear swelling=arthralgia, classically there is skin rash which is worse on exposure to sunlight, mouth ulcers are common, and then there is lots of extraarticular involvement as it’s a multisystem disease, so the kidneys can be affected, there may be haematological abnormalities with low cell counts, particularly low lymphocyte counts and low platelet counts, there may be pleural effusions so that’s fluid around the lung, pericardial effusion-fluid around the heart related to inflammation.
Sjogren’s syndrome-This has some relation to lupus, and this is characterised by dry eyes, dry mouth, so dry mucous membranes caused by destruction of the salivary glands and the lacrimal glands in the eye, but again lupus has a number of extra articular features.
Thirdly there’s scleroderma, and this is characterised by vasculopathy, so damage to blood vessels, and in particular patients with scleroderma get this marked Reynauld’s phenomenon, which can even result in ischaemia of the fingers. There tends to be skin thickening and there may also be fibrosis of internal organs.
Finally there is polymyositis, which is an autoimmune disease causing muscle inflammation. Clinically this results in muscle weakness and high creatinine kinase on blood tests.
These are the diseases that if you suspect, you should then go on to order an ANA test.
Anti-nuclear antibodies (ANA) interpretation:
ANA interpretation:
- Strength of ANA is reported as a number which is the maximal dilution at which the antibody is still detectable
eg 1:80 (weak), ie after 80 dilutions the ANA was still detectable but at no further dilutions
1: 320,
1: 640,
1: 1280 (strong or high level eg strongly positive test), ie up to 1280 dilutions it was detectable but not after this.
2. Negative test rules out SLE
3. 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 eg strongly positive ANA result in a patient with a photosensitive rash, joint pain and protein in urine, is highly suggestive of lupus.
If the ANA is positive…
What do you do next? 3 tests:
If ANA is positive we need to do some further testing, to try and narrow down exactly what the autoantibody is that’s causing it to be positive. You can think of the ANA as a screening test
First test we need to do is an ENA test:
ENA (extractable nuclear antigens): a panel of 5 autoantibodies
- Ro -Ro can be positive in Lupus or Sjogrens syndrome
- La -Lupus or Sjogrens syndrome
- RNP -Lupus or mixed connective tissue disease (overlap Connective Tissue disease with features of lupus, scleroderma and myositis
- Smith -More specific for Lupus
- Jo-1 Polymyositis (muscle inflammation)
Other test to order:
Double stranded (dsDNA) antibodies: highly specific for lupus, associated with renal involvement, useful for tracking lupus activity over time within a patient eg when patient is in remission it will fall and when they have a flare it will rise
Other test=Complement levels C3 and C4: may be ↓ in active lupus
Part 2: synovial fluid analysis
Can give steroid injection at same time as joint aspiration, as long as we are confident there is no infection present.
-Send for microscopy culture and sensitivity and this enables identification of causative organism to guide antibiotic choice
Second use is to diagnose gout and pseudogout
Crystal arthritis: synovial fluid analysis
For crystal detection used polarised light!
In pic can see needle shaped crystals from a patient with gout.
Septic arthritis vs. reactive arthritis: key differences
septic arthritis-bacteria can be grown from joint
Whereas in reactive arthritis the inflammation is sterile. It is not an infection in the joint, it’s an immunlogical reaction to an infection elsewhere eg a sexually transmitted infection or a previous bout of gastroenteritis.
For reactive arthritis-wouldn’t give antibiotics unless found they had clamydia or something for example, and this needed treatment.
Part 3: imaging tests in rheumatology
Osteoarthritis: radiographic (X-ray) features
Subchondral boney sclerosis shows as increased white appearence on X-ray
Osteophytes=bone spurs
Osteoarthritis: radiographic features
narrowing of joint space shown in both which reflects wearing out of the normal cartilage layer.
Osteoarthritis: radiographic features
Rheumatoid arthritis: imaging
Boney erosions occur only in established disease ie permanent change. This we try to prevent from happening at all.
X-ray not useful in early RA as only detects boney structure which are a late finding, ultrasound is much better
Radiographic changes in Rheumatoid Arthritis vs. Osteoarthritis
RA vs OA
Left-RA
- There is erosion and resorption of the distal ulnar
- There are marked erosions at the MCP joints
- There is ulnar deviation of the fingers
Whereas in osteoarthritis
- Metocarpophalangeal joints are spared, nice clean joint space. But there are changes at the DIP joints, with increased whitening which is subchondral sclerosis
Gout: radiographic features
-After the first few attacks of gout the X-ray is maybe normal, but if the disease has been going on for many years, overtime there might be boney changes-rat bites.
Psoriatic arthritis
- Asymetry of joints nvolved
- Sparing of MCP joints but IPJs are affected
- can see in right hand little finger there’s the beginning of a ‘pencil and cup deformity’ at that proximal interphalangeal joint.
The value of MRI
Went on to perform MRI which revealed abnormality-avascular necrosis of femoral head. Bone has become infarcted due to impairment of blood supply. Very serious, can potentially destroy the hip.
Put her on crutches so not weight bearing so she could recover without the need for Surgery
