Notes on Musculoskeletal Disorders

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Bone disorders:

Osteogenesis imperfecta:

• Brittle bone disease.

• AD disease.

• Defective type I collagen.

• Findings: fractures, blue sclera, deafness.

Achondroplasia:

• AD disease.

• Impaired growth plate cartilage proliferation.

• Findings: normal sized head/vertebral column; short limbs.

• Normal GH and IGF-1.

Osteopetrosis:

• AR disease.

• Defective osteoclasts.

• Fractures, anemia, CN compression.

Osteomyelitis:

• Bone infection due to: S aureus (most common).

• Findings: fever, bone pain.

• In sickle cell anemia: S. paratyphi.

• In foot due to rubber footwear puncture: P. aeruginosa.

Osteoporosis:

• Loss of bone matrix and minerals.

• Primary: idiopathic, senile, postmenopausal (lack of estrogen).

• Secondary: disease, drugs, space travel.

• Prevention: vitamin D, calcium, weight-bearing exercise.

• Treatment: bisphosphonates, calcitonin.

Legg-Calve-Perthes disease:

• Aseptic necrosis of femoral head.

Osgood-Schlatter disease:

• Boys 11-15 years old.

• Proximal tibial apophysis inflammation at patellar tendon insertion.

Paget's disease: osteitis deformans:

• Elderly men.

• Idiopathic.

• Osteoclastic resorption of bone; shaggy-appearing lesions.

• Increased alkaline phosphatase.

• Thick weak bone - mosaic bone.

• Increased osteoclastic bone resorption causing increased bone turnover.

• Osteoclasts in Paget's disease are large and multinucleated, and originate from mononuclear phagocytic cell lineage.

• RANK-L and M-CSF play important roles in osteoclastic differentiation.

• Causes may include paramyxovirus infection.

• Some findings include: bone pain and deformity, hearing loss.

• Positive tartrate-resistant acid phosphatase stain (TRAP).

Fibrous dysplasia:

• Benign, non-neoplastic process.

• Replacement of marrow with fibrous tissue.

• Associated with Albright's syndrome.

Joint disorders:

Osteoarthritis:

• Non-inflammatory joint disease.

• Universal after 65 years of age.

• Degeneration of articular cartilage in weight-bearing joints.

• Osteophyte formation.

• Bone rubs on bone.

Findings:

• PIP/DIP enlargement.

Neuropathic arthropathy (Charcot's joint):

• Non-inflammatory joint disease.

• Secondary to neurologic disease.

Causes:

• Diabetes mellitus, syringomyelia, tabes dorsalis.

Rheumatoid arthritis:

• HLA-DR4 association.

• Type III hypersensitivity reaction.

• Joint B-cells produce rheumatoid factor.

• Rheumatoid factors activate complement, attracting neutrophils.

• Synovial tissue proliferates forming a pannus.

• Findings: MCP/PIP involved; knees, ankles, hips involved; lungs, hematologic disease, carpal tunnel syndrome, rheumatoid nodules, vasculitis, popliteal cyst.

Sjogren's syndrome:

• Autoimmune disease; dominant in females.

• Destruction of salivary and lacrimal glands.

• Findings: rheumatoid arthritis, dry eyes, dry mouth.

• Labs: anti-SS-A (Ro) and anti-SS-B (La) antibodies.

• Confirm with lip biopsy.

Juvenile rheumatoid arthritis:

• Children younger than 16.

• Still's disease: fever, rash, polyarthritis; lymphadenopathy, neutrophilic leukocytosis.

Gouty arthritis:

• Multifactorial inheritance.

• Due to underexcretion of uric acid.

• Recurrent acute arthritis: podagra (gout in great toe; painful); fever, pain, neutrophilic leukocytosis.

• Chronic gout: tophi cause erosive arthritis.

Findings:

• Urate neuropathy, renal stones, hypertension, coronary artery disease, lead poisioning.

Labs:

• Hyperuricemia.

Chondrocalcinosis (pseudogout):

• Degenerative joint disease.

Seronegative spondyloarthropathies:

• HLA-B27 +.

• Three types:

• Ankylosing spondylitis: affects sacroiliac joint in young men; bamboo spine.

• Reiter's syndrome: urethritis due to C. trachomatis; arthritis and Achilles tendon periostitis.

• Psoriatic arthritis: sausage-shaped DIP joints (toe or finger); pencil-in-cup deformity.

Septic arthritis:

• S. aureus and N. gonorrhoeae.

• C6-C9 deficiency predisposes young women to disseminated gonococcemia.

Lyme disease:

• B. burgdorferi.

• Ixodes tick transmission; white-tailed deer is reservoir.

• Early: bull's eye lesion.

• Late: arthritis, Bell's palsy, myocarditis and pericarditis; babesiosis (secondary infection).

• Diagnosis: serologic tests, biopsy, silver stains.

Septic arthritis and tendinitis due to cat bite:

• P. multocida.

Muscle disorders: neurogenic atrophy:

• Type I and II fiber atrophy.

Muscle disorders:

Duchenne's muscular dystrophy:

• Deficiency of dystrophin gene.

• XR disease.

• Type I and II fiber atrophy.

• Weakening and wasting of pelvic muscles.

• Death by age 20.

• Labs: increased serum creatine kinase at birth; increased serum creatine kinase in female carriers.

Myotonic dystrophy:

• AD disease.

• Trinucleotide repeat disorder.

• Findings: facial weakness, myotonia, frontal balding, cataracts, testicular atrophy, cardiac involvement.

• Increased serum creatine kinase.

Myasthenia gravis:

• Thymus-synthesized auto-antibodies against ACh receptors.

Findings:

• Ptosis, dysphagia, risk for thymoma.

Confirmation:

• Tensilon (edrophonium) test.

Soft tissue disorders: fibromatosis:

• Fibrous tissue infiltrates muscle tissue.

• Dupuytren's contracture; desmoids tumor.

Additional Reading:

Basic Pathology

1. Cell Injury
2. Inflammation and Repair
3. Immunopathology
4. Water, Electrolyte, Acid-Base, Hemodynamic Disorders
5. Genetic and Developmental Disorders
6. Environmental Pathology
7. Nutritional Disorders
8. Neoplasia
9. Vascular Disorders
10. Heart Disorders
11. Red Blood Cell Disorders
12. White Blood Cell Disorders
13. Lymphoid Tissue Disorders
14. Hemostasis Disorders
15. Blood Banking and Transfusion Disorders
16. Upper and Lower Respiratory Disorders
17. Gastrointestinal Disorders
18. Hepatobiliary and Pancreatic Disorders
19. Kidney Disorders
20. Lower Urinary Tract and Male Reproductive Disorders
21. Female Reproductive and Breast Disorders
22. Endocrine Disorders
23. Musculoskeletal Disorders
24. Skin Disorders
25. Nervous System Disorders
26. Notes on Tissue Regeneration
27. A Table of Bleeding Disorders
28. FAQ on Structure and Function of Red Blood Cells
29. FAQ on Components of Blood
30. Notes on Hemostatic Mechanisms
31. What is Fever?
32. What is Edema?
33. FAQ on Blood Pressure
34. FAQ on principles of fluid and flow dynamics of Blood
35. Causes of Thrombocytopenia
36. Squamous cell carcinoma of head and neck mucosa
37. Four tumors which never metastasize to the brain
38. What is caustic injury?
39. What causes Peripheral Edema?

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