Week 6: Rheumatology (3) (investigations) Flashcards
Investigations in rheumatology
- Bloods (FBC, U and E, uric acid, LFTs, CK
- Inflammatory markers (ESR, PV, CRP)
- Human leukocyte antigen B25 (HLA_B27)
- Urinalysis
- Synovial fluid analysis
- Biopsy
- NCS and EMG
- X-ray
- US
- MRI
interpreting blood results: Hb
- Anaemia of chronic disease most common in RA, Fe deficiency may be due to NSAIDs
interpreting blood results: platelets
- Rise with
- inflammation or bleeding
- Fall in SLE
interpreting blood results neutrophils
- Rise with
- inflammation, sepsis and prednisolone usage;
- Fall in SLE or with DMARD toxicity
interpreting blood results: lymphocytes
- Falls in
- SLE or DMARD induced
interpreting blood results: U and E
- Rise due to
- NSAIDs
- renal disease in lupus/vasculitis or gout
interpreting blood results: uric acid
- rise in gout
- fall with inflammation
interpreting blood results: LFTs
- Rise due to Hepatitis due to DMARD toxicity
interpreting blood results: CK, ALT, LDH
- Rise in myositis
inflammatory markers
ERS
PV
CRP
ESR
- Erythrocyte sedimentation rate
- Reference range men <50 yrs (<5mm/h); women < 50 yrs, (<7mm/h) ; rises in pregnancy ;both sexes> 50 yrs (<30mm/h)
- Test reflects presence of: fibrinogen and immunoglobulins
- Effect of anaemia- rises
- Advantages
- Widely understood
- Well established in diagnosis and monitoring of GCA
- Disad
- No technique for calibration to test for accuracy
- Poor reproducibility
- Test takes 2 hour
- Must be carried out within 4 hours of blood sampling
PV
- Plasma viscosity
- Reference range independent of age & sex (1.5-1.72 mPa)
- Test reflects presence of: fibrinogen and immunoglobulins
- Anaemia has no effect
- Advantages
- Automatable
- Sensitive
- Not affected by haematocrit
- Measurement can eb made on stored sample
- Disadvantages
- Not widely used- lack of familiarity with interpretation
CRP
- C-reactive protein
- Reference range variable but constant within individuals (<10 mg/L)
- Anaemia has no effect
- Advantages
- Automatable
- Very sensitive
- Not affected by haematocrit
- Measurement can be made on stored blood samples
- Disad
- Short lived indicator
- Good at monitoring sepsis as rises and falls quickly
- Short lived indicator
autoantibodies found in RA
RF and anti-CCP
autoantibodies found in OA
N/A
autoantibodies found in Sjogrens
Anti- Ro and Anti-La
RF and anti ds-DNA
auotantibodies found in SLE
ANA
Anti-dsDNA
Anti-Ro, Anti-La
Raised ESR or PV
decreased:
- C3 and C4 decrease with disease activity
autoantibodies found in polymyalgia rheumatica
Raised ESR or CRP
autoantibodies found in spondyloarthropathies
HLA-B27 gene
- Ankylosing spondylitis- raised CRP
- Psoriatic arthritis- CRP raised
- Reactive arthritis- CRP raised
autoantibodies found in raynauds
Associated with scleroderma, SLE, dermatomyositis and polymyositis, Sjoren’
autoantibodies found in vasculitis
ANA, ANCA, RF
C3, C4
autoantibodies found in systemic sclerosis (SSc)
ANA
Anti-centromere- limited SSc
Scl-70 (topoisomerase) and antiRNA polymerase III- diffuse SSc
autoantibodies found in polymycositis
Anti-Jo1
Human leukocyte antigen B27 (HLA-B27)
- HLA-B27 is a class 1 surface antigen. It is found in around 10% of white people. Its prevalence varies with ethnicity.
- It is strongly associated with ankylosing spondylitis, iritis and juvenile arthritis.
- Around 90% of white people with AS are positive for this.
Urinalysis
Renal disease may first be detected by the presence of protein and/or blood on a urine dipstick. This test is mandated in SLE and vasculitis.
Synovial fluid analysis
- This is the most important investigation in suspected cases of septic arthritis and crystal arthropathy.
- Send immediately for gram stain and culture, before antibiotic treatment if possible.
- Polarized light microscopy may reveal negatively birefringent needle shaped crystals in gout or positively birefringent rhomboid shaped crystals in pseudo gout.
Biopsy
- Temporal artery biopsy is the most common biopsy requested by rheumatologists. However, due to the patchy nature of vascultis in GCA false negatives may occur.
- Muscle biopsy for polymyositis or dermatomyositis
- Skin biopsy is useful in vasculitis, dermatomyositis and SLE
- Lip/salivary gland biopsy for Sjogren’s
- Lymph node biopsy may be needed in SLE to rule out lymphoma or TB
- Synovial biopsy may be needed for rare tumours or infections
- Sural nerve biopsy uncommonly requested but helpful in vasculitis with mononeuritis multiplex/periph neuropathy Renal biopsy for vasculitis, SLE
NCS (nerve conduction studies) & EMG (electromyography)
- NCS help to confirm peripheral nerve entrapment e.g. carpal tunnel syndrome.
- EMG records spontaneous and voluntary muscle activity and has characteristic abnormalities in myositis.
X-ray
The least expensive and most easily available initial investigation. Avoid unnecessary x-rays to minimize radiation risk. Good for assessing bone. Often normal in inflammatory arthritis for up to 5 years after diagnosis. Reflects damage rather than any ongoing disease activity.
RA X-ray
- (LESS) - think MCJ
- Loss of joint space
- Erosions
- Soft tissue swelling
- Subluxation
OA X-ray
- Joint space narrowing
- Subarticular sclerosis
- Bone cyst
- Osteophytes
Ultrasound
Used mainly for diagnosis of early synovitis and erosions in early RA and PsA. Good for soft tissue structures like bursae and tendons. May be used to guide joint injections and soft tissue injections such as for tenosynovitis. Simple, portable & cheap. Very operator dependent. Difficult to independently review images obtained.
Magnetic resonance imaging (MRI)
Expensive but good for identification of early inflammation especially in spondyloarthritis. Highly reproducible. Very good for knee and shoulder – to look for meniscal and ligament tears and rotator cuff tears. Useful in cases of suspected infection or neoplasia. Also used for investigation of myositis. Contraindications are: claustrophobia/pacemaker/metal body in eye/surgical clips in brain.
Dual energy X-ray absorptiometry (DEXA)
Radiation dose about 1/10 of CXR dose.
Evaluation for osteoporosis. Estimates bone mineral density at different sites i.e hip, spine and forearm. T score indicates BMD of the patient compared to a normal person of same age and sex.
Osteoporosis is diagnosed when the T score is less than 2.5 standard deviations below the mean.
