lecture 25

Question 1

What is arthritis?

Answer 1

• derived from Greek words
• ‘arthron’ = joint
• ‘itis’ = inflammation
• literally means ‘inflamed joint’
• umbrella term rather than a single disease
• > 100 different types of arthritis currently identified
• disability and reduced quality of life (elderly)

Question 2

What is the prevalence of arthritis in the Australian Population?

Answer 2

• in 2011-12
• approx, 3.3 million (1 in 6; ~15%) had arthritis
• prevalence higher in indigenous than non-indigenous
• 95% of cases due to osteoarthritis
• less commonly rheumatoid arhtritis, gout
• in 2012 total cost of arthritis and musculoskeletal conditions
• • $55.1 billion
• based on current trends, by the year 2050, 7 million australians expected to suffer some form of arthritis

Question 3

What is a definition of rheumatoid arthritis?

Answer 3

• chronic inflammatory autoimmune disease of unknown aetiology
• associated with
• • articular manifestations (dominant feature)
• • systemic (or ‘extra-articular’) complications

Question 4

What does RA lead to in the absence of effective treatment?

Answer 4

• progressive locomotor disability within 10-20 years of diagnosis
• reduced life expectancy of up to 10 years
• significant socioeconomic costs - also loss of gainful employment

Question 5

What is the primary manifestation of RA?

Answer 5

• synovitis
• primary manifestion is synovial inflammation of ‘synovitis’
• -> erosion of bone, cartilage, peri-articular structures

Question 6

What is the epidemiology of RA?

Answer 6

• in adult caucasian populations
• incidence 8 to 98 cases per 100,000/annum (new cases diagnosed)
• prevalence 0.5 to 1.0% (number of diagnosed patients over a given point in time)
• occurs 2-3x more commonly in females than males
• peak age of onset 40 (range 40 - 70) years

Question 7

What is the principle of all autoimmune diseases?

Answer 7

cocktail of ingredients before someone gets an autoimmune disease:
- genetic susceptibility
plus
- environmental trigger (not always known)

leads to breakdown of immune tolerance (self-reactive antibody or T cells)

consequence of this is autoimmune disease

Question 8

What are risk factors for RA?

Answer 8

• multifactorial
  i. genetic
  ii. epigenetic
  iii. hormonal
  iv. stochastic (random) environmental triggers

Question 9

What are genetic risk factors for RA?

Answer 9

• HLA
• studies of identical twins
• • genetics accounts for 50-60% of disease susceptibility

genetic risk factors

i. human leukocyte antigen (HLA) ~ 12.7%
ii. non-HLA ~4%

• HLA Class II (most important)
• DRB1 gene
• • encodes HLA-DR antigen presenting molecule
• allelic variant
• • DRB1*0401
• • DRB1*404

Question 10

What is the location and organisation of HLA complex? What allelic variants contribute to RA?

Answer 10

• chromosome 6
• short arm
• this area can be divided into three broad regions: class II, class III, class I
• within the class II region, it is the DRB1 which has been associated with increased risk of RA
• RA HLA risk alleles: HLA-DRB10401 and DRB10404
• with this allele risk increased approximately 4 fold

Question 11

What is the shared epitope hypothesis?

Answer 11

HLA-DRB1 alleles (confer RA risk) encode a five amino acid sequence termed a ‘shared epitope’

• glutamic-leucine-arginine-alanine-alanine (QKRAA)
• occupies positions 70 to 74 of the HLA-DRβ chain
• surrounds peptide binding groove (determines antigen-binding specificity and presentation to CD4+ T helper cells)

Question 12

What is the proposed role of shared epitope?

Answer 12

i. efficient binding of arthritogeneic (citrulline) peptides
ii. marker of immunoreactivity
- anti-citrullinated protein antibodies (ACPA) expression
iii. thymic selection of autoimmune T cells (+ve or -ve)
iv. target for T cells
- molecular mimicry - SE and microbes (e.g. epstein-barr virus)
v. polarises T-cell differentiation to T helper type 17 (autoimmunity)

Question 13

What is the susceptibility associated with shared epitope in RA?

Answer 13

Does not necessarily predict progression to RA
- cohort with recent-onset undifferentiated (ACPA+) arthritis, progression to RA occured regardless of HLA-DR genotype

May predict RA severity

• increased joint damage e.g. increased erosions (two copies)
• increased prevalaence of extra-articular manifestations

Question 14

What is microchimerism?

Answer 14

• possible explanation SE not associated with RA in ceratin ethnic and racial groups
• maternal cells of SE-expressing women persist in their children’s circulation throughout adulthood –> confers increased RA risk
• termed non-inherited maternal antigens (NIMA)

Question 15

What are non-HLA genetic risk factors for RA?

Answer 15

gene, odds ratio for RA, function

• PTPN22, ~2 fold, encodes lymphoid tyrosine phosphatase; role in T and B cell signalling, no role in RA risk in asians
• PADI4, ~2 fold, primarily asian populations
• TRAF1-C5, b/w 1.2 and 2 fold: encodes TNF-associated factor and complement protein 5c
• STAT4, b/w 1.2 and 2 fold: encodes a tf that controls genes involved in Th1 cell responses
• TNFAIP3, b/w 1.2 and 2 fold: encodes TNF-induced protein 3
• IL2/21, b/w 1.2 and 2 fold: –
• CCR6, – , encodes chemokine-receptor 6
• NLRP1, – , encodes inflammasome-related protein (only in Han Chinese)

Question 16

What is epigenetics?

Answer 16

• modification of a chromsome that leads to altered gene expression, without changing DNA (i.e. nucleotide base) sequences
• may be heritable

Question 17

What are epigenetic mechanisms in RA?

Answer 17

• histone deacetylase increased in RA
• DNA methylation - fibroblast-like synoviocytes and T cells
• microRNAs (miRNA)

Question 18

What are hormonal risk factors of RA?

Answer 18

oestrogen exposure

• B cells (produce autoantibodies) more resistant to apoptosis
• fibroblast-like synoviocytes (FLS) - increased metalloproteinases
• macrophage cell line - increased TNF

pregnancy

• 1st and 2nd trimester: >75% improve (huge progesterone and oestrogen surge)
• 3rd trimerster: remission (lots of oestrogen circulating)
• postpartum: 90% flare

Question 19

What is citrullination?

Answer 19

• post-translational conversion of the amino acid arginine to citrulline by peptidyl-arginine deiminase (PADI) enzymes
• • intra- or extra-cellular
• • neoepitopes serve as targets for autoimmunity
• • citrulline binds shared epitope more avidly
• • immune tolerance breakdown –> ACPA

induction of PADI expression and peptide citrullination is not specific to the joint or RA and occurs in many different settings of tissue stress/inflammation

humans have four isoforms of PADI
- PADI2 and PADI4 abundant in inflamed synovium

=NH –> =O

Question 20

What are environmental risk factors of RA?

Answer 20

• RA first described in 1800 (not demonstrated pre-19th century/industrial revolution) - “new world [environmental] pathogen or allergen”
• smoking (PADI2) (monozygotic twins - 12 of 13 who smoked got it, involved in citrullination process)
• bronchial stress
• • exposure to silica, traffic pollution (Nurses’ health study)
• infections (or their products e.g. heat shock protein)
• • porphyromonas gingivalis (peridontal disease, PADI4)
• epsetin-barr virus, cytomegalovirus, proteus species, excherichia coli
• Toll-like receptor (TLR) activation
• • increased peptidyl-arginine delminase (PADI) expression
• • directly cause arthritis (e.g. streptococcus via TLR2)
• Microbiome
• • Two (germ-free) mouse models of RA (K/BxN, IL-1Ra-deficient): bacteria induced arhtritis
• • dietary changes or antibiotics –> equilibrium protective and pathogenic intestinal bacteria altered –> induction innate immune system in genetically predisposed host

Question 21

What are clinical features of RA?

Answer 21

• primary manifestation is synovial inflammation or ‘synovitis’
• • inflammatory pannus of cells
• • particularly fibroblasts and macrophages
• • progressive erosion and damage of articular and periarticular structures

Question 22

What are articular (joint) manifestations?

Answer 22

when presenting to physcian:

• morning stiffness - ≥ 1 hour, ≥ 6 weeks
• • needs to be greater than 6 weeks because some viral diseases mimic rheumatoid
• pain
• swelling

distribution

i. symmetrical: i.e. involvement of one hand should be identical to the other side
ii. most commonly affected joints
- upper limbs
- - metacarpophalangeal (MCP)
- - proximal interphalangeal (PiP)
- - wrist
- lower limbs
- - metatarsophalangeal (MTP)

• Boutonniere deformity
• subluxed fingers
• swan neck deformity
• ulnar deviation

Question 23

What is the Boutonniere deformity?

Answer 23

• flexion of the PiP joint

- extension of the DiP joint

Question 24

What happens with uncontrolled MCP swelling?

Answer 24

• subluxed finger

- slip downwards because of inflammation

Question 25

What is the swan neck deformity?

Answer 25

- exetended PiP | - flexed DiP

Question 26

How do we differentiate RA from Osteoarthritis (OA)?

Answer 26

RA vs OA Age at onset - childhood and adults, peak incidence in 50s vs - increases with age Predisposing factors - susceptibility epitopes (HLA-DR4, HLA-DR1), PTPN22, PADI4 polymorphisms, and others - smoking vs - trauma - congenital abnormalities (e.g. shallow acetabulum) Early symptoms - morning stiffness vs - pain increases through the day and with use Joints involved - metacarpophalangeal joints, wrsits, proximal interphalangeal joints most often; distal interphalangeal joints almost never vs - Distal interphalangeal joints (Herberden's nodes) - Weight bearing joints (hips, knees) Physical findings - soft tissue swelling, warmth vs - bony osteophytes, minimal soft tissue swelling early Radiologic findings - periarticular osteophenia, marginal erosions vs - subcondrial sclerosis, ostephytes Laboratory findings - increased C-reactive protein, rheumatoid factor, anticitrullinated protein antibody, anaemia, leukocytosis vs - normal

Question 27

What is a useful discriminator of RA vs OA?

Answer 27

- distribution (pattern) of joint involvement RA - very symmetrical - classic involvement of the wrists - PiP joint involvement - MCP - soft tissue swelling OA - can affect the spine - can be symmetrical but frequently asymmetrical - DiP joint involvement - base of thumb - bony swelling

Question 28

What are extra-articular manifestions of RA?

Answer 28

RA can involve almost any organ system you can think of With the advent of treatment most patients don't suffer extra-articular manifestations anymore marker of severity shortens both quality and quantity of a patients life Nodules - subcutaneous - pulmonary - cardiac - firm rubbery lumps Pulmonary - pieuritis/pleural effusion - fribrosing alveolitis Ocular - scleritis - episcleritis - keratoconjuctivitis sicca (KCS) - very bad if left untreated Vasculitis - systemic - cutaneous - mononeuritis multiplex Neurological - nerve entrapment - cervical myelopathy Cardiovascular - ischaemic heart disease (IHD) - pericarditis/pericardial effusion - conduction defects - stroke Cutaneous - palmar erythema - ulceration - pyoderma gangrenosum - neutrophillic dermatoses Haematologic - anaemia - feity's syndrome - amyloidosis Malignancy - lymphoma/lymphoproliferative disease - large granular lymphocyte syndrome - lung cancer - skin cancer

Question 29

What antibodies are typically present in RA? Can these be used to diagnose RA?

Answer 29

Rheumatoid factor (RF) - high-affinity autoantibody against the Fc portion (epitopes) of immunoglobulin IgG - prior to RA onset: increase IgM or IgA isotype Anti-citrullinated protein antibodies (ACPA) - antibodies against citrullinated 'self-proteins' - detected via anti-cyclic citrullinated peptide (CCP) assay - - alpha-enolase, keratin, fibrinogen, fibronectin, type II collagen, vimentin - prior to RA onset: increased titre, avidity, epitope spreading, isotype changes Autoantibodies can develop years before the onset of RA symptoms - ACPA seen up to 14 years before - RF about 10.5 years before disease symptom onset

Question 30

What is sensitivity and specificity of testing?

Answer 30

Test positive: - if disease present: A, true positive, (sensitivity) - disease absent: B, false positive Test negative - disease present: C, false negative - disease absent: D, true negative, specificity ``` sensitivity = A/(A+C) [SNNout] specificity = D/(B+D) [SPPin] ``` positive likelihood ratio = sensitivity / (1 - specificity) negative likelihood ratio = (1 - sensitivity)/specificity

Question 31

What is the diagnostic utility of autoantibodies in RA?

Answer 31

Sensitivity, % (95% CI) - IgM RF: 70 (66-73) - - i.e. not 100% at picking up everyone who's got the condition - ACPA: 67 (64-70) - - still not 100% Specificity, % (95% CI) - IgM RF: 79 (74-83) - - a lot of other conditions that can give you a falsely elevated RF without getting RA - ACPA: 95 (94-96) - - specificity, not a lot of diseases outside of RA that will causes presence of ACPA Positive likelihood ratio (95% CI) - IgM RF: 3.3 (2.7-3.9) - ACPA: 14.5 (11.6-18.0) Negative likelihood ratio - IgM RF: 0.39 (0.35 - 0.42) - ACPA: 0.35 (0.32-0.38)

Question 32

When testing for antibodies, what are two subsets of RA? What is this a predictor of?

Answer 32

i. seropositive - RF or ACPA positive ii. seronegative - RF or ACPA negative - prognositic information: seropositivity is a predictor of: - radiographic progression - extra-articular manifestations - functional impairment

Question 33

How is RA disease activity assessed?

Answer 33

Joint counts * - tender and/or swollen Global assessment * - physician and patient Pain score * - visual analogue score Morning stiffness * - >60 minutes Laboratory * - erythrocyte sendimentation rate (ESR) - C-reactive protein (CRP) Disability Fatigue Radiological damage * - erosive changes on serial radiographs - on average x-rays every 1 - 2 years - is it getting worse? - if so escalate treatment

Question 34

What is teh DAS28-ESR calculator?

Answer 34

- tender joint count - swollen joint count - marker of inflammation: ESA, CRP - patient global health

Question 35

What are DAS28 cutoff criteria?

Answer 35

Disease activity in 28 joints using C-reactive protein (CRP) or Erythrocyte sedimentation rate (ESR) - DAS28-CRP, or DAS28-ESR - DAS28 < 2.6: remission - DAS28 ≥ 2.6 and ≤ 3.2: low disease activity - DAS28 > 3.2 and ≤ 5.1: moderate disease activity - DAS28 > 5.1: high disease activity objective way of monitoring/scoring patients progress/control remission is goal for all patients with RA even with clinical remission: subclinical inflammation remains possible (imaging studies)

Question 36

Take home messages of RA?

Answer 36

- autoantibodies utility - - diagnostic, classify, prognositc - assessing disease activity - - composite indices (DAS28-CRP/-ESR) - differentiating OA from RA - - distribution (pattern) of joint involvement - arthritis: not a single entity, burden of disease