Classification of arthritis according to harrison
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I now have comprehensive content from Harrison's Chapter 382. Let me compile the full classification of arthritis as presented in Harrison's Principles of Internal Medicine 22nd Edition.
Classification of Arthritis According to Harrison's
(Harrison's Principles of Internal Medicine, 22nd Edition (2025) - Chapter 382: Approach to Articular and Musculoskeletal Disorders)
Core Framework: Four Key Questions
Harrison's classifies arthritis by first answering four fundamental questions:
- Articular or nonarticular?
- Inflammatory or noninflammatory?
- Acute or chronic?
- Monoarticular, oligoarticular, or polyarticular?
By combining these dimensions, any presentation can be characterized - e.g., "acute inflammatory monoarthritis" or "chronic noninflammatory polyarthritis" - to narrow the differential diagnosis.
I. Based on Pathologic Process: Inflammatory vs Noninflammatory
A. Inflammatory Arthritis
Suggested by the cardinal signs of inflammation (erythema, warmth, pain, swelling), systemic features (fever, rash, weight loss), or lab evidence (elevated ESR/CRP, thrombocytosis, anemia of chronic disease). Morning stiffness is prolonged (hours) and improves with activity.
Subtypes of inflammatory arthritis:
| Subtype | Examples |
|---|---|
| Infectious | N. gonorrhoeae, M. tuberculosis, staphylococci, streptococci, viral, fungal, parasitic |
| Crystal-induced | Gout (monosodium urate), Pseudogout (CPPD) |
| Immune-mediated / Autoimmune | Rheumatoid arthritis (RA), Systemic Lupus Erythematosus (SLE) |
| Reactive | Rheumatic fever, Reactive arthritis (post-enteric or post-chlamydial) |
| Idiopathic | Conditions without identified cause |
B. Noninflammatory Arthritis
No synovial swelling or warmth, no systemic features, intermittent "gel phenomenon" (stiffness brief, ≤45 min, exacerbated by activity), and normal laboratory investigations.
Subtypes:
| Subtype | Examples |
|---|---|
| Degenerative / Ineffective repair | Osteoarthritis (OA) |
| Traumatic | Rotator cuff tear, internal derangements |
| Repetitive use | Bursitis, tendinitis |
| Neoplastic | Pigmented villonodular synovitis (PVNS) |
| Pain amplification | Fibromyalgia |
II. Based on Number of Joints Involved
| Category | Definition | Typical Examples |
|---|---|---|
| Monoarthritis | 1 joint | Septic arthritis, gout, pseudogout, trauma |
| Oligoarthritis (Pauciarticular) | 2-4 joints | Reactive arthritis, psoriatic arthritis, spondyloarthropathies |
| Polyarthritis | ≥5 joints | RA, SLE, viral arthritis, disseminated gonococcal infection |
"Red flag" presentations - septic arthritis, acute crystal arthritis, and fracture - are typically acute monoarticular and require immediate evaluation.
III. Based on Chronology
| Category | Definition |
|---|---|
| Acute | Onset within days to weeks |
| Chronic | Persistent beyond 6 weeks |
IV. Based on Etiology (Broader Classification)
1. Infectious Arthritis
- Acute bacterial arthritis - S. aureus, streptococci, gram-negatives
- Gonococcal arthritis - most common in sexually active young adults
- Spirochetal - Lyme arthritis, syphilitic arthritis
- Mycobacterial - TB arthritis (subacute/chronic monoarthritis)
- Fungal arthritis
- Viral arthritis - hepatitis B/C, parvovirus, chikungunya, HIV-related
- Parasitic arthritis
2. Crystal-Induced Arthritis
- Gout (monosodium urate crystals)
- Pseudogout / CPPD disease (calcium pyrophosphate dihydrate crystals)
3. Immune-Mediated / Autoimmune Arthritis
- Rheumatoid Arthritis (RA)
- Systemic Lupus Erythematosus (SLE)
- Sjögren's syndrome
- Polymyalgia Rheumatica (PMR)
- Vasculitis-associated arthritis
4. Spondyloarthropathies (SpA)
- Axial Spondyloarthritis (axSpA) - including ankylosing spondylitis
- Psoriatic Arthritis
- Reactive Arthritis (formerly Reiter's syndrome)
- IBD-Associated Arthritis (Crohn's, ulcerative colitis)
5. Degenerative / Metabolic Arthritis
- Osteoarthritis (OA) - primary and secondary
- Neuropathic arthropathy (Charcot's joint)
- Hemochromatosis-related arthropathy
6. Nonarticular / Periarticular Disorders (often misidentified as arthritis)
- Bursitis, tendinitis, enthesitis
- Fibromyalgia
- Fasciitis
V. Distinguishing Features: Inflammatory vs Noninflammatory
| Feature | Inflammatory | Noninflammatory |
|---|---|---|
| Morning stiffness | Prolonged (hours), improves with activity | Brief (≤45 min, "gel phenomenon"), worsens with activity |
| Synovial swelling/warmth | Present | Absent |
| Systemic symptoms | Fever, rash, weight loss | Absent |
| Lab abnormalities | Elevated ESR, CRP, thrombocytosis, anemia | Normal |
| Fatigue | Profound | Variable |
VI. "Red Flag" Diagnoses (Require Urgent Evaluation)
- Septic arthritis - acute monoarthritis with fever
- Acute crystal-induced arthritis (gout, pseudogout) - acute monoarthritis with erythema
- Fracture - acute focal pain after trauma
Source: Harrison's Principles of Internal Medicine, 22nd Edition (2025) - Chapter 382, "Approach to Articular and Musculoskeletal Disorders," by John J. Cush
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