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CP reviewer 1 > Diagnosing Autoimmune Disease > Flashcards

Diagnosing Autoimmune Disease Flashcards

1
Q

Case 1

History

  • 51 yo lady
  • 18month history of SOB on exertion
  • Saw respiratory team and diagnosed with pulmonary fibrosis
  • Fatigue, aches and pains
  • Thickening of skin on hands and changes in the skin around her mouth

Examination

  • Sclerodactyly both hands
  • Livedo reticularis on the legs
  • Cool feet on palpation

Diagnosis? Treatment?

A

Scleroderma (diffuse systemic sclerosis) and started immunosuppression treatment

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2
Q

What tests are required to confirm autoimmune diseases?

A
  • ANA
  • ANCA
  • CK
  • Rheumatoid Factor
  • Anti-CCP antibody
  • Complement
  • FBC U&Es LFTs CRP
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3
Q

What is ‘ANA’? What does it mean when ANA is positive?

A

The antibodies that target “normal” proteins within the nucleus of a cell are called antinuclear antibodies (ANA).

In most cases, a positive ANA test indicates that your immune system has launched a misdirected attack on your own tissue — in other words, an autoimmune reaction.

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4
Q

What is sensitivity of a test?

A

measure of how good the test is in identifying people with the disease

(a = true positive, c = false negative)

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5
Q

What is specificity of a test?

A

measure of how good the test is at correctly defining people without the disease

(b= False positive, d= True negative)

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6
Q

How is a positive predictive value calculated?

A

The proportion of people with a positive test who have the target disorder –> [a/(a+b)]

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7
Q

How is a negative predictive value calculated?

A

The proportion of people with a negative test who do not have the target disorder.

[d/(c+d)]

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8
Q

Test diagrams:

  • What does moving cut-off to right result in?
  • What does moving cut-off to left result in?
A
  • Right –> reduces false positive (higher sensitivity) at cost of reduced specificity
  • Left –> reduces false negatives (higher specificity) at cost of reduced sensitivity
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9
Q

What are 2 categories of diagnostic test?

A

Non Specific:

  • Inflammatory markers

Disease specific:

  • Autoantibody testing
  • HLA typing
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10
Q

What are the non specific markers of systemic inflammation?

A
  • ESR
  • CRP
  • Ferritin
  • Fibrinogen
  • Haptoglobin
  • Albumin
  • Complement
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11
Q

Different types of antibodies are associated with different autoimmune diseases. What auto-antibody is associated with:

a) SLE?
b) rheumatoid arthritis?

A

a) dsDNA
b) CCP

E.g. A positive ANA is seen in many other conditions whereas a positive anti-dsDNA is fairly specific for SLE

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12
Q

How is SLE tested for?

A

98% of all people with systemic lupus have a positive ANA test, making it the most sensitive diagnostic test for confirming diagnosis of the disease.

More tests are performed to check for other antibodies that can help to confirm the diagnosis. Certain autoantibodies and substances in the blood can give information about which autoimmune disease is present. To check for these antibodies, doctors usually order what is called an ANA panel, which checks for the following antibodies: anti-double-stranded DNA, anti-Smith, anti-U1RNP, anti-Ro/SSA, and anti-La/SSB. So

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13
Q

What are complement levels like in SLE?

A

Low complement levels often signify active lupus

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14
Q

How does lupus affect the kidneys? What is creatinine result?

A

Lupus nephritis is a type of kidney disease caused by SLE.

U&E test done:

  • Creatinine levels high
    • Creatinine is a waste product from the normal breakdown of muscles in your body. Y
    • our kidneys remove creatinine from your blood.
    • Health care professionals use the amount of creatinine in your blood to estimate your glomerular filtration rate (GFR).
    • As kidney disease gets worse, the level of creatinine goes up.
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15
Q

What is Rheumatoid Factor (RF)?

A
  • Antibody (IgM, IgG or IgA) directed against the Fc portion of IgG
  • Rheumatoid factors are proteins produced by your immune system that can attack healthy tissue in your body.
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16
Q

What is an RF test used for?

A

A rheumatoid factor test is one of a group of blood tests primarily used to help pinpoint a diagnosis of rheumatoid arthritis.

N.B. commonly found in rheumatoid arthritis but not diagnostic of the disease (sensitivity and specificity around 70%)

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17
Q

In what other diseases can RF be seen in?

A

In diseases in which polyclonal stimulation of B cells is seen (chronic infections)

18
Q

What is ACPA?

A

Anti-CCP Antibody –> Anti-CCPs are antibodies also produced by the immune system

19
Q

What is an ACPA test used to diagnose?

A
  • More specific (95%) for rheumatoid arthritis than RF (similar sensitivity)
  • Useful prognostic marker
20
Q

How is ACPA used as a prognositc marker?

A

•ACPA positive patients tend to have more severe and erosive disease

21
Q

What is an ESR test?

A

An erythrocyte sedimentation rate (ESR) is a type of blood test that measures how quickly erythrocytes (red blood cells) settle at the bottom of a test tube that contains a blood sample. Normally, red blood cells settle relatively slowly. A faster-than-normal rate may indicate inflammation in the body.

22
Q

Typical results of; RhF, CCP, ESR and CRP in rheumatoid arthritis?

A

High RhF, CCP, ESR and CRP add to the probability of a definitive diagnosis

23
Q

What is ANCA?

A

Anti neutrophil cytoplasmic antibodies –> test is most often used to find out if you have a type of autoimmune vasculitis

24
Q

What is Granulomatosis with polyangitis (formerly called Wegener’s granulomatosis)?

A

An uncommon disorder that causes inflammation of the blood vessels in your nose, sinuses, throat, lungs and kidneys.

25
Q

What are the two main types of ANCA?

A

Each targets a specific protein inside white blood cells:

  1. pANCA, which targets a protein called MPO (myeloperoxidase)
  2. cANCA, which targets a protein called PR3 (proteinase 3)
26
Q

What antigen does cANCA mainly target?

A

PR3 (90%)

27
Q

What antigen does pANCA mainly target?

A

MPO

28
Q

cANCA stain

A

Granular fluorescence of neutrophil cytoplasm with nuclear sparing

29
Q

pANCA stain

A

Apparent fluorescence of the peri-nucleus only

30
Q

Anti-neutrophilic cytoplasmic antibodies (ANCA) associated systemic vasculitides

A
31
Q

What would a positive ANCA indicate?

A

It may mean you have autoimmune vasculitis. It can also show if cANCAs or pANCAs were found. This can help determine which type of vasculitis you have.

32
Q

Clinical utility of ANCA testing:

A
  • Positive ANCA; useful in suggesting the diagnosis in the proper clinical setting
  • Histopathology remains the gold standard for diagnosis in most cases
  • Negative ANCA assays do not exclude AASV
    • 10%-50% of patients may be ANCA neg
  • Persistence of ANCA in the absence of clinical indications of active disease does not indicate a need for continued treatment
  • Reemergence of ANCA pos in a patient who was ANCA neg whilst in remission
    • Suggests a risk of disease flare.
33
Q

Which antibodies are useful in diagnosing autoimmune liver disease?

A
  • Anti-mitochondrial Ab –> specific for primary biliary sclerosis
  • Anti-smooth muscle and anti-liver/kidney/microsomal (LKS) Abs –> found in autoimmune hepatitis
  • Antibodies detected by IF screening using rodent tissue block (oesophagus, liver and kidney) and antigen specific ELISA
34
Q

When would you perform tests for autoimmune liver disease?

A

If liver tests were deranged

35
Q

What autoantibodies are found in type 1 diabetes?

A
  • islet cell antibodies
  • anti-GAD65 anti-GAD67
  • anti-insulinoma antigen 2 (IA-2)
  • insulin autoantibodies (IAAs)

These disappear with progression of disease and total destruction of β islet cells

36
Q

When would an autoantibody test be done in type 1 diabetes?

A
  • Disease confirmation
  • to identify relatives and patients at risk of developing autoimmune diabetes
37
Q

What is Addison’s disease?

A

(Also called adrenal insufficiency) occurs when your adrenal glands don’t produce enough cortisol and, often, too little aldosterone.

38
Q

What antibodies are found in Addison’s disease?

A

Autoantibodies targeting the adrenal cortex which impairs the production of cortisol

39
Q

Which antigen is targeted in pernicious anaemia?

A
  • H+K+-ATPase located in the gastric parietal cells of stomach –> Antibody present in more than 90% of patients with Pernicious anaemia.
  • Antibodies to GPC and intrinsic factor
40
Q

What is autoimmune gastritis? What does it lead to?

A

Autoimmune gastritis is a chronic inflammatory disease with destruction of parietal cells of the corpus and fundus of the stomach. The known consequence is vitamin B12 deficiency and, consequently, pernicious anemia.

41
Q

How do we test for anti-nuclear antibodies?

A
  • Indirect immunofluorescence
  • ELISA
  • Microbead immunoassay
  • Immunoblot
42
Q

What disease is associated with anti neutrophil cytoplasmic antibodies (ANCA)?

A

Small vessel vasculitis

CP reviewer 1 (59 decks)

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