1. Osteoarthritis (OA)
Etiology:
- Age-related cartilage degeneration
- Obesity (weight-bearing joints)
- Previous joint trauma or surgery
- Genetic predisposition
Clinical Features:
- Pain that worsens with activity and improves with rest
- Morning stiffness lasting <30 minutes
- Crepitus, joint line tenderness, and bony swelling
- Restricted range of motion (ROM)
- Common sites: knees, hips, cervical/lumbar spine, DIP joints (Heberden’s nodes)
High-Yield Differentiating Feature:
- Asymmetrical joint involvement, especially weight-bearing joints
- Presence of bony outgrowths (osteophytes)
- Minimal systemic symptoms
Differential Diagnosis:
- Rheumatoid Arthritis (RA) – symmetrical joint involvement, prolonged morning stiffness, systemic symptoms
- Gout – acute onset, red and hot joint
- Psoriatic arthritis – associated skin lesions, nail pitting
Symptom Assessment:
- Joint pain character and duration
- Relation with activity/rest
- Functional limitations
- History of trauma or repetitive use
Diagnostics:
- X-ray: Joint space narrowing, osteophytes, subchondral sclerosis, cysts
- ESR/CRP: Usually normal
- Joint aspiration: Non-inflammatory fluid
2. Rheumatoid Arthritis (RA)
Etiology:
- Autoimmune disorder targeting synovial joints
- Female predominance (20-50 years)
- HLA-DR4 association
Clinical Features:
- Symmetrical polyarthritis – affects small joints first (MCP, PIP, wrists)
- Morning stiffness lasting >1 hour
- Joint deformities (ulnar deviation, swan-neck, boutonnière)
- Extra-articular features: nodules, anemia, scleritis, lung fibrosis
High-Yield Differentiating Feature:
- Symmetrical small joint involvement + prolonged morning stiffness
- Positive Rheumatoid Factor (RF) and Anti-CCP antibodies
Differential Diagnosis:
- OA – larger joints, asymmetrical, less morning stiffness
- SLE arthritis – no erosions, reversible joint symptoms
- Viral arthritis – self-limited, short duration
Symptom Assessment:
- Joint pattern, stiffness duration, constitutional symptoms
- Family history, systemic signs
Diagnostics:
- Blood tests: RF (70%), Anti-CCP (high specificity)
- Elevated ESR/CRP
- X-ray: Marginal erosions, periarticular osteopenia, joint space narrowing
3. Gout
Etiology:
- Hyperuricemia (diet rich in purines, alcohol, CKD, diuretics)
- Male predominance
- Metabolic syndrome association
Clinical Features:
- Sudden onset of severe joint pain, swelling, and redness
- Classically affects 1st MTP joint (podagra)
- Pain at night, triggered by alcohol/food
- Tophi in chronic gout
High-Yield Differentiating Feature:
- Monoarticular arthritis of 1st toe, rapid onset, and tophus formation
- Crystal identification: Needle-shaped, negatively birefringent under polarized light
Differential Diagnosis:
- Septic arthritis – fever + systemic illness + purulent aspirate
- Pseudogout – affects knee, rhomboid crystals, positively birefringent
- RA – symmetrical, chronic, systemic features
Symptom Assessment:
- Alcohol/diet history, sudden pain, location, recurrence
Diagnostics:
- Serum uric acid: Often elevated, may be normal during attack
- Joint aspiration: Monosodium urate crystals
- X-ray: Erosions with overhanging edges in chronic cases
4. Ankylosing Spondylitis (AS)
Etiology:
- Chronic inflammatory disease of axial skeleton
- Young males (teens to 30s), HLA-B27 positive
Clinical Features:
- Chronic low back pain, better with exercise, worse at rest
- Morning stiffness >30 minutes
- Reduced spine mobility – positive Schober test
- Sacroiliac joint tenderness
- Extra-articular: anterior uveitis, aortic regurgitation
High-Yield Differentiating Feature:
- Insidious onset back pain in young male + improvement with activity + sacroiliitis
- Bamboo spine in late stage
Differential Diagnosis:
- Mechanical back pain – no stiffness, worsens with activity
- Disc herniation – radicular pain, neuro signs
- Psoriatic arthritis – similar axial involvement but with skin lesions
Symptom Assessment:
- Age at onset, activity relationship, stiffness duration
- History of uveitis or psoriasis
Diagnostics:
- X-ray pelvis: Sacroiliitis, syndesmophytes, bamboo spine
- MRI: Early changes
- HLA-B27: Positive
- ESR/CRP: Elevated
5. Septic Arthritis
Etiology:
- Hematogenous spread or direct inoculation (trauma, surgery)
- Common organisms: Staphylococcus aureus, Neisseria gonorrhoeae
Clinical Features:
- Acute monoarthritis, intense pain, fever, and swelling
- Joint held in semi-flexed position
- Reduced ROM, tender, warm joint
High-Yield Differentiating Feature:
- Hot, swollen, tender joint with fever and systemic toxicity
- Requires emergency management
Differential Diagnosis:
- Gout – no fever, crystals in aspirate
- RA flare – no acute systemic signs
- Reactive arthritis – post-infectious, usually polyarthritis
Symptom Assessment:
- Fever, trauma, immunocompromised state, joint involved
Diagnostics:
- Joint aspiration: Purulent, WBC >50,000/mm³, Gram stain & culture
- Blood culture: Positive in 50%
- X-ray: May show joint space narrowing or destruction in late stages
6. Osteoporosis
Etiology:
- Postmenopausal estrogen deficiency
- Age-related, sedentary lifestyle
- Long-term corticosteroids, thyroid disorders
Clinical Features:
- Silent disease until fracture occurs
- Common fractures: vertebral compression, Colles’ fracture, hip fracture
- Loss of height, kyphosis
High-Yield Differentiating Feature:
- Fragility fractures with normal calcium/phosphate levels
- T-score ≤ -2.5 on DEXA
Differential Diagnosis:
- Osteomalacia – bone pain, proximal myopathy, low Vitamin D
- Multiple myeloma – pathological fractures, anemia, hypercalcemia
Symptom Assessment:
- Fracture history, risk factor evaluation, lifestyle
Diagnostics:
- DEXA scan: Gold standard
- Serum calcium, phosphate: Normal
- ALP: Normal or mildly elevated
- X-ray: Vertebral collapse, increased radiolucency
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