Epidemiology:
- Prevalence of RA 0.5-1.0% in general population
- In 2005,
approximately 1.5 million US adults (0.6%) had RA
- The most recent US data on incidence of RA is from the Rochester Epidemiology Project:
- From 1995-2007,
41 per 100,000 people were diagnosed with RA each year
- Increased incidence with age: 8.7 per 100,000 people among those aged 18-34 compared with 54 per 100,000 among those aged ≥ 85 years
- Incidence peaked among people aged 65-74 years: 89 per 100,000
- From 1995 to 2007 rates increased by 2.5% each year among women but there was a small decrease (0.5%) in men
Pathophysiology
– It is thought that RA is triggered by a combination of genetic and stochastic random events,
with repeated activation of innate immunity leading to RA
– Genetic susceptibility to RA is most importantly linked to HLA major histocompatability genes although many other minor genes including cytokine promoters and T cell signaling genes also contribute
– However,
genes are not the only influence as studies have shown a concordance rate for identical twins of only 12-15%
– Smoking is thought to represent one of the most important environmental stimuli contributing to RA,
increasing risk by 20 to 40 fold
– An important element is the induction of the peptidyl arginine deiminase (PAD) enzymes,
which convert arginine to citrulline
- In RA it appears that increased citrullination leads to the production of anti-citrullinated protein antibodies,
contributing to the clinical manifestations of disease
Clinical Presentation
– Chronic inflammatory disease manifesting as damage of synovial-lined joints as well as extra-articular manifestations
– Typically found in metacarpophalangeal,
proximal interphalangeal and metatarsophalangeal joints,
as well as in the wrists and knee
– Articular and periarticular manifestations include joint swelling and tenderness to palpation,
with morning stiffness
– Extra-articular involvement includes:
- Other visceral involvement
– The natural history of RA varies although three possible disease courses are noted:
- Monocyclic: Have one episode which ends within 2-5 years of initial diagnosis and does not reoccur.
This may result from early diagnosis and/or aggressive treatment
- Polycyclic: The level of disease activity fluctuates over the course of the condition
- Progressive: RA continues to increase in severity and is unremitting
Radiographs are relatively insensitive in the detection of early osseous erosions
Magnetic resonance imaging (MRI) has been shown to be useful in the clinical management of RA:
- Can detect preerosive synovitis
- Can identify early bone damage prior to radiographic manifestations
- Has been shown to predict future bone damage
In this presentation we review various MRI manifestations of RA,
specifically: