Musculoskeletal Made Simple For NLE NRE Step 1

1. Gout

• Cause: Increased serum uric acid → deposition of monosodium urate (MSU) crystals in joints.
• Common Site:
  • 1st MTP joint (great toe) → Podagra.
  • Subcutaneous tissue → Tophi.
• Lab Findings:
  • Serum uric acid (S. UA) > 7.5 mg/dL.
  • Joint aspiration → Needle-shaped, negatively birefringent crystals (under polarized light).
• Clinical Features:
  • Acute: Joint pain, swelling, redness, tenderness.
• Treatment:
  • Acute attack: NSAIDs (first-line).
  • Chronic management:
    • Allopurinol (xanthine oxidase inhibitor).
    • Febuxostat (alternative; side effect = diarrhea).
• Drug Interaction:
  • Allopurinol + Azathioprine → Severe bone marrow suppression.

2. Pseudogout

• Cause: Deposition of calcium pyrophosphate crystals.
• Lab Findings:
  • Joint aspiration → Rhomboid-shaped, positively birefringent crystals.

3. Rheumatoid Arthritis (RA) vs Osteoarthritis (OA)

4. Behcet’s Syndrome

Key Features (Triad)

• Genital ulcers
• Oral ulcers (recurrent, painful)
• Ocular involvement (uveitis, conjunctivitis)

Associations

• HLA-B51 positive (strong genetic link)
• Autoimmune/vasculitis nature
• ANA may be positive (non-specific)

Treatment

• Immunosuppressants:
  • Cyclosporine
  • Azathioprine
  • Tacrolimus

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5. Felty’s Syndrome

• Triad:
  • Rheumatoid Arthritis (RA)
  • Splenomegaly
  • Neutropenia

6. Caplan’s Syndrome

• Seen in patients with Rheumatoid Arthritis (RA) + pneumoconiosis.
• Characterized by:
  • Lung nodules (multiple, round).
  • Associated with occupational dust exposure (e.g., coal workers).

7. Septic Arthritis

Definition

Inflammation of a joint due to bacterial infection.

Common Causes

• Staphylococcus aureus (most common)
• Gram-negative rods (e.g., E. coli, Pseudomonas)

Clinical Features

• Severe joint pain
• High-grade fever, chills, rigors
• Redness, swelling, tenderness of affected joint

Investigations

• Joint aspiration (gold standard)
  • ↑ WBC count (>80,000/mm³)
  • Gram stain & culture → identifies organism
• Blood tests → leukocytosis, ↑ ESR/CRP

Treatment

• Empiric antibiotics:
  • Ceftriaxone + Vancomycin (cover Gram+ and Gram–)
• Drainage of joint fluid (arthrocentesis or surgical washout)
• Modify antibiotics according to culture results

8. Bone Tumors – Quick Review

• E = Epiphysis → Giant cell tumor
• D = Diaphysis → Ewing sarcoma
• M = Metaphysis → Osteosarcoma

9. Osteosarcoma

• Age: 10–20 years
• Weight: 40–60 kg
• X-ray:
  • Sunburst appearance
  • Codman’s triangle

10. Seronegative Arthritis – Ankylosing Spondylitis

• Joint Involvement: Inflammation of sacroiliac joint
• Associations:
  • Anterior uveitis
  • Heart block
• Investigations:
  • X-ray: Fusion of the sacroiliac joint, squaring of the lumbar vertebrae
  • MRI: Bamboo spine
  • Lab: ↑ CRP, Rheumatoid factor (–ve)
• Treatment:
  • NSAIDs
  • Muscle relaxants

11. Reactive Arthritis (Reiter’s Syndrome)

• Triad:
  • Conjunctivitis
  • Arthritis
  • Urethritis

12. Psoriatic Arthritis

• Joint involvement: Commonly DIP joints
• X-ray: Pencil-in-cup deformity

13. Important Antibodies & Their Associated Conditions

14. Polymyositis

• Meaning: Poly = many, myositis = muscle inflamed
• Clinical feature:
  • Progressive muscle weakness (esp. proximal muscles → difficulty standing, climbing stairs, combing hair)
  • No skin involvement (distinguishes from dermatomyositis)
• Antibody: Anti-Jo-1 antibody
• Diagnosis: Muscle biopsy (gold standard)
• Treatment: Steroids (first-line)

15. Dermatomyositis

Muscle involvement:

• Progressive muscle weakness (proximal > distal)

Skin involvement:

• Heliotrope rash → around eyelids
• Gottron’s papules → over knuckles
• Shawl sign → rash on shoulders

Antibody: Anti-Mi-2 antibody

Diagnosis: Muscle biopsy

Treatment: Steroids (first-line)

16. Systemic Lupus Erythematosus (SLE)

• Type: Autoimmune disease (multisystem involvement)
• Epidemiology:
  • F > M
  • Younger age group

Clinical Features

• Skin → Malar rash, photosensitivity
• Joints → Arthralgia
• Blood → Anemia
• Renal → Impairment (nephritis)
• Neuro → Neural involvement (seizures, psychosis)
• General → Fatigue

Laboratory

• ANA → Positive (sensitive)
• Anti-dsDNA → Positive (specific)
• Drug-induced SLE → Anti-histone antibody

Note

• Mild SLE (no renal, no neuro involvement) → Better prognosis

17. Systemic Sclerosis (Scleroderma)

• Pathology → Excess collagen (types I & III) → skin hardening
• Types:
  • Limited (CREST syndrome) → Anti-centromere antibody
    • C → Calcinosis
    • R → Raynaud phenomenon
    • E → Esophageal dysmotility
    • S → Sclerodactyly
    • T → Telangiectasia
  • Diffuse → Widespread organ involvement
• Tx → ACE inhibitors (esp. for renal crisis)

18. Sjogren Syndrome (autoimmune, exocrine destruction)

• Glands involved → Lacrimal & salivary → dry eyes + dry mouth
• Antibodies:
  • Anti-Ro (SSA) → Positive
  • Anti-La (SSB) → Decreased
  • ANA → Positive
• Diagnostic test → Schirmer test < 5 mm
• Treatment:
  • Artificial tears
  • Pilocarpine (↑ secretions)