Week 6: Rheumatology (3) (investigations)

Question 1

Investigations in rheumatology

Answer 1

• 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

Question 2

interpreting blood results: Hb

Answer 2

• Anaemia of chronic disease most common in RA, Fe deficiency may be due to NSAIDs

Question 3

interpreting blood results: platelets

Answer 3

• Rise with
  
  • inflammation or bleeding
  • Fall in SLE

Question 4

interpreting blood results neutrophils

Answer 4

• Rise with
  
  • inflammation, sepsis and prednisolone usage;
  • Fall in SLE or with DMARD toxicity

Question 5

interpreting blood results: lymphocytes

Answer 5

• Falls in
  
  • SLE or DMARD induced

Question 6

interpreting blood results: U and E

Answer 6

• Rise due to
  
  • NSAIDs
  • renal disease in lupus/vasculitis or gout

Question 7

interpreting blood results: uric acid

Answer 7

• rise in gout
• fall with inflammation

Question 8

interpreting blood results: LFTs

Answer 8

• Rise due to Hepatitis due to DMARD toxicity

Question 9

interpreting blood results: CK, ALT, LDH

Answer 9

• Rise in myositis

Question 10

inflammatory markers

Answer 10

ERS

PV

CRP

Question 11

ESR

Answer 11

• 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

Question 12

PV

Answer 12

• 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

Question 13

CRP

Answer 13

• 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

Question 14

autoantibodies found in RA

Answer 14

RF and anti-CCP

Question 15

autoantibodies found in OA

Answer 15

N/A

Question 16

autoantibodies found in Sjogrens

Answer 16

Anti- Ro and Anti-La

RF and anti ds-DNA

Question 17

auotantibodies found in SLE

Answer 17

ANA

Anti-dsDNA

Anti-Ro, Anti-La

Raised ESR or PV

decreased:

• C3 and C4 decrease with disease activity

Question 18

autoantibodies found in polymyalgia rheumatica

Answer 18

Raised ESR or CRP

Question 19

autoantibodies found in spondyloarthropathies

Answer 19

HLA-B27 gene

• Ankylosing spondylitis- raised CRP
• Psoriatic arthritis- CRP raised
• Reactive arthritis- CRP raised

Question 20

autoantibodies found in raynauds

Answer 20

Associated with scleroderma, SLE, dermatomyositis and polymyositis, Sjoren’

Question 21

autoantibodies found in vasculitis

Answer 21

ANA, ANCA, RF

C3, C4

Question 22

autoantibodies found in systemic sclerosis (SSc)

Answer 22

ANA

Anti-centromere- limited SSc

Scl-70 (topoisomerase) and antiRNA polymerase III- diffuse SSc

Question 23

autoantibodies found in polymycositis

Answer 23

Anti-Jo1

Question 24

Human leukocyte antigen B27 (HLA-B27)

Answer 24

• 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.

Question 25

Urinalysis

Answer 25

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.

Question 26

Synovial fluid analysis

Answer 26

• 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.

Question 27

Biopsy

Answer 27

• 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

Question 28

NCS (nerve conduction studies) & EMG (electromyography)

Answer 28

• 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.

Question 29

X-ray

Answer 29

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.

Question 30

RA X-ray

Answer 30

• (LESS) - think MCJ
  
  • Loss of joint space
  • Erosions
  • Soft tissue swelling
  • Subluxation

Question 31

OA X-ray

Answer 31

• Joint space narrowing
• Subarticular sclerosis
• Bone cyst
• Osteophytes

Question 32

Ultrasound

Answer 32

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.

Question 33

Magnetic resonance imaging (MRI)

Answer 33

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.

Question 34

Dual energy X-ray absorptiometry (DEXA)

Answer 34

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.