Approach to Articular and Musculoskeletal Disorders¶
Chapter 382 | Part 11: Immune-Mediated, Inflammatory, and Rheumatologic Disorders
KEY CLINICAL POINTS¶
- Distinguish between articular (joint) and nonarticular (periarticular) musculoskeletal disorders using pain characteristics, range of motion, and swelling.
- Red flag conditions include septic arthritis, gout, and fractures, requiring urgent evaluation.
- Inflammatory disorders (e.g., RA, gout) present with swelling, warmth, and systemic symptoms, while noninflammatory conditions (e.g., OA, fibromyalgia) lack these features.
- Use the algorithm in Figure 382-1 to guide differential diagnosis based on chronology, pathology, and systemic features.
- Synovial fluid analysis (via polarized microscopy) is critical for diagnosing crystal-induced arthritis (gout/pseudogout) and infection.
1. DEFINITION & OVERVIEW¶
Musculoskeletal disorders encompass articular (joint) and nonarticular (periarticular) conditions. Articular structures include synovium, cartilage, and ligaments, while nonarticular structures involve tendons, bursae, and muscles. Nonarticular pain is more common and may mimic arthritis. Key features include deep pain with swelling in articular disorders vs. focal tenderness in nonarticular conditions.
Table 382-1: Evaluation of Patients with Musculoskeletal Complaints¶
| Goal | Approach |
|---|---|
| Accurate diagnosis | Determine chronology (acute vs. chronic) |
| Timely provision of therapy | Assess inflammatory vs. noninflammatory process |
| Avoidance of unnecessary testing | Anatomic localization (articular vs. nonarticular) |
| Identification of red flags | Determine extent of involvement (monoarticular, polyarticular) |
1.1 Articular vs. Nonarticular Disorders¶
Articular disorders: Deep pain, limited range of motion, swelling, crepitus. Nonarticular disorders: Focal tenderness, pain with active motion, no swelling. Nonarticular conditions (e.g., tendinitis, fibromyalgia) often mimic arthritis.
1.2 Red Flag Conditions¶
Urgent evaluation is needed for septic arthritis, acute crystal-induced arthritis (gout/pseudogout), and fractures. These present with acute onset, monoarticular pain, and systemic symptoms.
2. EPIDEMIOLOGY¶
Musculoskeletal disorders affect 1 in 3 U.S. adults (127 million). 54.4 million have physician-diagnosed arthritis. Common conditions include OA (50% of adults >65), RA (1%), gout (men), and fibromyalgia (2-4% of women). Age-related risks: OA, osteoporosis, and fractures in elderly; gout and pseudogout in middle-aged men.
2.1 Demographics¶
OA: 15-25% of outpatient visits. RA: 1% prevalence. Gout: 3.9 million in U.S. (men > women). Fibromyalgia: 2-4% of women. PMR: 0.1-0.3% of adults >50.
2.2 Risk Factors¶
Trauma, repetitive strain, obesity, diabetes, renal insufficiency, and medications (e.g., corticosteroids) increase risk. Age >60: OA, osteoporosis, fractures. Men: gout, spondyloarthritis. Women: RA, osteoporosis.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Inflammatory disorders (infectious, crystal, autoimmune) vs. noninflammatory (trauma, degenerative, neoplastic). Crystal-induced arthritis (gout: monosodium urate; pseudogout: calcium pyrophosphate). Autoimmune: RA (synovitis), SLE (vasculitis). Noninflammatory: OA (cartilage degeneration), fibromyalgia (central pain amplification).
Table 382-2: Drug-Induced Musculoskeletal Conditions¶
| Condition | Associated Drugs |
|---|---|
| Arthralgias | Quinidine, beta blockers, statins, HIV protease inhibitors |
| Myalgias/myopathy | Glucocorticoids, penicillamine, statins, cyclosporine |
| Tendon rupture/tendinitis | Quinolones, glucocorticoids, statins |
| Gout | Diuretics, alcohol, fructose-containing soft drinks |
| Drug-induced lupus | Hydralazine, procainamide, phenytoin |
3.1 Crystal-Induced Arthritis¶
Gout: monosodium urate crystals (polarized microscopy: needle-shaped, negative birefringence). Pseudogout: calcium pyrophosphate dihydrate (rhomboid-shaped, positive birefringence).
3.2 Autoimmune Mechanisms¶
RA: T-cell mediated synovitis, pannus formation. SLE: autoantibodies (ANA, anti-dsDNA), vasculitis. Psoriatic arthritis: HLA-B27, enthesitis.
4. CLINICAL FEATURES¶
Acute vs. chronic presentation. Articular: swelling, warmth, limited motion. Nonarticular: focal tenderness. Inflammatory: prolonged morning stiffness, systemic symptoms (fever, weight loss). Noninflammatory: intermittent stiffness (<45 min), fatigue. Red flags: fever, rash, joint effusion.
4.1 Pain Characteristics¶
Articular: Deep, diffuse pain with swelling. Nonarticular: Focal, localized tenderness. Fibromyalgia: Widespread pain with no objective findings.
4.2 Systemic Symptoms¶
Inflammatory: Fever, weight loss, anemia. Noninflammatory: Fatigue, sleep disturbances. SLE: Rash, serositis. RA: Morning stiffness >30 min.
5. DIFFERENTIAL DIAGNOSIS¶
Articular: RA, gout, septic arthritis. Nonarticular: Fibromyalgia, tendinitis, bursitis. Crystal-induced: Gout (monoarticular), pseudogout (oligoarticular). Inflammatory: SLE, vasculitis. Noninflammatory: OA, PMR, myopathy.
5.1 Articular vs. Nonarticular¶
Articular: Swelling, warmth, limited motion. Nonarticular: Focal tenderness, no swelling. Fibromyalgia: Widespread pain with no objective findings.
5.2 Crystal-Induced Arthritis¶
Gout: Acute monoarticular pain, tophi, hyperuricemia. Pseudogout: Chronic, symmetric, calcification (chondrocalcinosis).
6. INVESTIGATIONS & DIAGNOSIS¶
Laboratory tests: ESR, CRP, uric acid, RF, ANA. Imaging: X-ray (OA, fractures), MRI (inflammation, necrosis), ultrasound (tendinitis, bursitis). Synovial fluid analysis: Polarized microscopy for crystals, Gram stain for infection. Algorithms: Figure 382-1 for differential diagnosis.
Table 382-4: Antinuclear Antibody (ANA) Patterns¶
| ANA Pattern | Antigen | Clinical Correlate |
|---|---|---|
| Diffuse | Deoxyribonucleoprotein | Nonspecific |
| Peripheral (rim) | ds-DNA | 50% SLE |
| Speckled | U1-RNP | MCTD |
| Centromere | Kinetochore | CREST syndrome |
6.1 Laboratory Tests¶
ESR/CRP: Inflammatory markers. Uric acid: Gout diagnosis. RF/ANA: Autoimmune disorders. CBC: Infection, anemia.
6.2 Imaging¶
X-ray: OA, fractures. MRI: Inflammation, necrosis. Ultrasound: Soft tissue abnormalities. CT: Spinal stenosis, fractures.
7. MANAGEMENT & TREATMENT¶
Acute: NSAIDs, colchicine (gout), antibiotics (infection). Chronic: DMARDs (RA), biologics (TNF inhibitors), corticosteroids. Nonpharmacologic: Physical therapy, weight management, exercise. Surgical: Joint replacement, arthroscopy for meniscal tears.
7.1 Acute Inflammatory Arthritis¶
Gout: Colchicine, NSAIDs, corticosteroids. Septic arthritis: IV antibiotics, arthroscopy. Pseudogout: NSAIDs, corticosteroids.
7.2 Chronic Conditions¶
RA: Methotrexate, TNF inhibitors. OA: NSAIDs, hyaluronic acid injections. Fibromyalgia: Pregabalin, CBT.
8. PROGNOSIS & COMPLICATIONS¶
Inflammatory disorders (RA, SLE): Risk of joint destruction, comorbidities (cardiovascular, renal). Noninflammatory: Chronic pain, disability. Complications: Osteonecrosis (corticosteroids), infection (immunosuppression), drug-induced myopathy.
8.1 Long-Term Outcomes¶
RA: Erosive joint damage without treatment. SLE: Renal failure, cardiovascular disease. Gout: Tophi, joint destruction.
8.2 Complications¶
Corticosteroid use: Osteonecrosis, myopathy. Immunosuppression: Infections, malignancy. Chronic pain: Depression, sleep disturbances.
9. SPECIAL CONSIDERATIONS¶
Pregnancy: Avoid NSAIDs, corticosteroids. Elderly: Osteoporosis, drug interactions. Pediatrics: Juvenile idiopathic arthritis, growth plate involvement. Telehealth: Virtual exams for range of motion, gait analysis.
9.1 Pregnancy¶
Avoid NSAIDs (third trimester), corticosteroids (risk of cleft palate). Use acetaminophen. Monitor for gestational hypertension.
9.2 Elderly Patients¶
OA, osteoporosis, fractures. Avoid NSAIDs (renal risk). Use low-dose corticosteroids. Monitor for drug interactions.
10. KEY POINTS & CLINICAL PEARLS¶
Use the algorithm in Figure 382-1 to guide diagnosis. Synovial fluid analysis is critical for crystal-induced arthritis. Distinguish between articular and nonarticular pain. Monitor uric acid levels in gout. Avoid NSAIDs in elderly patients. Telehealth can assess gait and range of motion.