Musculoskeletal Disorders — Clinical Application
| Disorder | Category | Primary Site Affected | Mechanism | Clinical Clue |
|---|---|---|---|---|
| Myasthenia gravis | Autoimmune | Neuromuscular junction | Autoantibodies destroy ACh receptors | Progressive weakness; ptosis; worse with activity; better with rest |
| Muscular dystrophy | Genetic | Skeletal muscle fiber | Dystrophin gene mutation (X-linked) | Progressive childhood weakness; calf pseudohypertrophy (in DMD) |
| Tetany | Metabolic | Nerves + muscles | Hypocalcemia → hyperexcitable neurons | Carpopedal spasm; Chvostek's sign; in hypoparathyroidism, vit D deficiency |
| Osteoarthritis | Degenerative | Articular cartilage | Wear-and-tear cartilage degradation | Elderly; weight-bearing joints; asymmetric; no morning stiffness |
| Rheumatoid arthritis | Autoimmune | Synovial membrane | T-cell/B-cell attack on synovium → pannus | Symmetric small joints; morning stiffness >1hr; young-middle age; anti-CCP |
| Osteoporosis | Hormonal/Metabolic | Bone mass/density | Osteoclast > osteoblast; estrogen deficiency | Post-menopausal women; fractures from minor trauma; low BMD on DEXA |
| Gout | Metabolic | Joint (urate crystals) | Hyperuricemia → monosodium urate crystal deposition | Big toe (podagra); acute onset; red, hot, swollen; men; purine-rich diet |
Autoimmune Disorder Comparison
- Myasthenia gravis: anti-ACh receptor antibodies → NMJ dysfunction → skeletal muscle weakness
- Rheumatoid arthritis: anti-CCP and rheumatoid factor → synovial inflammation → joint destruction
NEET Clinical Pattern Recognition
- "Weakness that worsens with exercise" → Myasthenia gravis
- "Joint pain in post-menopausal woman with fracture from minor fall" → Osteoporosis
- "Acute big toe pain after seafood dinner" → Gout
- "Symmetric joint swelling with morning stiffness in a 35-year-old" → Rheumatoid arthritis
- "Knee pain in a 70-year-old obese man, worsens on climbing stairs" → Osteoarthritis