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Pathology - Rheumatoid Arthritis
I. Definition & Epidemiology
RA can affect multiple organ systems:
RA has a variable course:
I. Definition & Epidemiology
- Definition: RA is a systemic autoimmune disease primarily affecting synovial joints. It's characterized by chronic inflammation.
- Epidemiology: Affects approximately 1% of the population, with a significantly higher prevalence in young to middle-aged women.
- Etiology (Cause): The initial trigger for RA remains unknown. However, once inflammation starts, it becomes self-sustaining.
- Pathogenesis (Mechanism):
- Inflammation: The synovium (joint lining) is infiltrated by CD4+ T-cells, B-cells, plasma cells, and macrophages, leading to inflammation.
- Pannus Formation: The inflamed synovium proliferates, forming pannus – a hyperplastic mass of synovial tissue.
- Joint Destruction: Pannus erodes articular cartilage, resulting in joint damage.
- Joint Involvement: Symmetrical swelling, pain, and stiffness, predominantly affecting small joints of the hands and feet. Morning stiffness is a characteristic symptom.
- Rheumatoid Factor (RF): An autoantibody targeting the Fc portion of IgG. Positive in ~70% of RA patients, but also found in other autoimmune diseases and some healthy individuals, limiting its specificity.
- Anti-citrullinated protein antibodies (ACPAs): Newer, more specific antibodies for diagnosing RA, but not as widely available as RF.
RA can affect multiple organ systems:
- Cardiovascular: Ischemic heart disease, pericarditis
- Vascular: Accelerated atherosclerosis, vasculitis
- Hematological: Anemia, splenomegaly
- Pulmonary: Pulmonary fibrosis, pleuritis
- Skin: Rheumatoid nodules, erythema nodosum, pyoderma gangrenosum
- Neurological: Peripheral neuropathy, stroke
- Amyloidosis: Deposition of serum amyloid A, leading to AA amyloidosis in various organs.
- Synovial Hyperplasia: Marked increase in synovial tissue.
- Inflammatory Infiltrate: A significant presence of lymphocytes and plasma cells.
- Germinal Centers: Formation of germinal centers within lymphoid aggregates is a typical finding.
RA has a variable course:
- Remission: Approximately 25% experience long-term remission.
- Mild-to-Moderate Disability: About 50% have chronic disease with mild-to-moderate disability.
- Severe Disability: Approximately 25% experience progressive disease leading to severe disability.
- Autoimmune nature: RA is driven by the body's immune system attacking its own tissues.
- Synovitis: Inflammation of the synovial membrane is central to the disease process.
- Pannus formation & joint destruction: Understand the sequence of events leading to joint damage.
- Diagnostic markers: Compare the sensitivity and specificity of RF and ACPAs.
- Systemic involvement: Be aware of the diverse extra-articular manifestations.
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