Musculoskeletal P athology Part I I Joints, Tendons, Tendon Sheaths, Bursae & Muscles

1. Musculoskeletal Pathology Part II Joints, Tendons, Tendon Sheaths, Bursae & Muscles

2. Joint diseases Congenital defects Dysplasia coxae congenita Trauma Degenerative diseases Osteoarthritis Inflammation Infective arthritis Lyme disease Tuberculous arthritis Rheumatoid arthritis Gout Tumours Pigmented villonodular synovitis

3. Dysplasia coxae congenita autosomal recessive congenital disorder hypoplasia of hip joint with congenital subluxation or luxation if left untreated →early secondary osteoarthritis

4. Trauma disruption of synovial membrane – bleeding into the join cavity (haemarthros) organization of haematoma – fibrous adhaesions limiting joint movements or ankylosis (joint space replaced by metaplastic bone) haemarthros often complicates disorders of coagulation (haemophilia)

5. Osteoarthritis most common of the joint diseases (14% of adult population) primary process is breakdown of the articular cartilage weight-bearing joints affected (hip, knee, intervertebral joints) Clinical features: pain, joint deformity, limitation of movement, crepitus (creaking sound heard on movement of the joint) Radiographic features: narrowing of joint space Two main groups: Primary OA: no known associated condition Secondary OA:degeneration of previously damaged joint (congenital disorders, inflammation, trauma)

6. Morphology erosive changes of joint cartilage („fibrillation“), flaking off of small portions of cartilage, later complete loss of cartilage – polishing of the denuded bone (smooth ivory-like surface) thickening of subchondral bone plate, synovial fluid under pressure enters into small defects in the bone →subchondral pseudocysts bony outgrowths at the margins of the articular cartilage (osteophytes)

7. Infective arthritis Staphylococcus aureus, Neisseria gonorrhoeae blood spread (most common), direct penetration (trauma) and direct spread from a contiguous infected site (osteomyelitis) hyperaemia and acute inflammatory infiltrate in the synovial membrane, exudate accumulation in the joint cavity (pyarthros) lysosomal enzymes released from neutrophils →severe damage of the articular cartilage – secondary osteoarthritis

8. Lyme disease spirochaete Borrelia burgdorferi transmitted to humans via tick bites systemic disease: skin, nervous system heart, joints Stage I: macular skin lesion (erythema migrans) + low-grade fever, headache, arthralgia, muscle pain, enlargement of regional lymph nodes Stage II: early bloodstream dissemination of borrelia: nervous system (meningitis, meningoencephalitis, neuritis), heart (atrioventricular block, pericarditis) Stage III: chronic disease (MorY after the initial infection): arthritis (large joints, similar to rheumatoid arthritis), nervous system (encephalopathy), skin (acrodermatitis chronica atrophicans Herxheimer)

9. Tuberculous arthritis children, haematogeneous dissemination knee, hip, elbow and ankle insidious development of pain, swelling and limitation of movement, other signs of inflammation mild or absent synovial hyperplasia, tuberculous granulomas in 90% of cases, acid-fast bacilli seldom identified

10. Rheumatoid arthritis common multisystem autoimmune disease three times as common in premenopausal women as in males small joints of the hands and feet, knees, hips, involvement frequently symmetrical rheumatoid factor (IgM) positive in 95% complication: secondary amyloidosis

11. Morphology hyperplasia of synovial membrane with increased vascularity, cellularity and synovial fluid production inflammatory infiltrate(lymphocytes and plasma cells), lymphoid follicles pannus (proliferation of inflammed hypervascular granulation tissue) degradation of articular cartilage, fibrous adhesions →joint movement severely limited, sometimes ankylosis (metaplastic bone), osteoporosis of adjacentbone deformities of joints (ulnar deviation of the fingers) periarticular rheumatoid nodules in 30% (central area of fibrinoid necrosis surrounded by macrophages and fibroblasts arranged in a palisaded fashion)

12. Variants of RA: Juvenile rheumatoid arthritis (JRA): individuals younger than 16 years, large joints predominantly involved, rheumatoid factor often negative Still’s disease (systemic JRA): fever, leucocytosis, enlargement of liver, spleen and lymph nodes Felty’s syndrome: RA + splenomegaly + neutropenia

13. Gout disorder of purine metabolism →hyperuricaemia 30 – 60 years, male preponderance deposition of monosodium urate crystals into articular cartilage, synovial membrane and periarticular soft tissues (tophi, tophaceous gout) Acute gouty arthritis: metatarsophalangeal joint of the big toe (70%), ankle, knee, wrist, elbow, the affected joint is red, hot, swollen, very painful and tender Chronic gouty arthritis: follows recurrent episodes of acute gouty arthritis, progressive erosion of cartilage and bone – limited joint function

14. Pigmented villonodular synovitis benign tumour rather than inflammatory condition knee joint (80%) mild pain, swelling, tenderness brown-coloured nodular thickening of synovial membrane villous synovial hyperplasia diffuse proliferation of mononuclear cells resembling histiocytes various number of osteoclast-like multinuclear giant cells depositions of hemosiderin

15. Diseases of tendons, tendon sheaths and bursae Ganglion area of myxoid degeneration of connective tissue of tendon sheath extensor surfaces of hand and feet thin walled pseudocyst containing mucoid fluid Tendovaginitis (inflammation of the tendon sheath) purulent, rheumatoid (serofibrinous), tuberculous Tendovaginitis stenosans (deQuervain): stenosis of the tendon sheath by accumulation of fibrocartilaginous tissue – discontinual movement of the affected finger (digitus saltans) Bursitis bursae around shoulder, elbow and knee Acute bursitis (mechanical overload): serofibrinous exudate Chronic bursitis (repeated traumatisation): fibrous thickening of the wall, hyperplasia of synovial lining and fibrin deposits

16. Diseases of skeletal muscle Muscle atrophy Muscle dystrophy Myasthenia gravis Inflammatory disorders (myositis)

17. Muscle atrophy Generalized: malnutrition, hypopituitarism, immobilisation Localized: immobilisation of one limb, denervation (trauma, neuritis, poliomyelitis) Microscopic features: decrease in size of muscle fibers

18. Muscle dystrophy heterogeneous group of genetically determined disorders spontaneous progressive degeneration of muscle fibers microscopic features: different size of muscle fibers (combination of atrophy and hypertrophy), degenerative changes (fragmentation of the sarcoplasma, necrosis), signs of regeneration (cells with basophilic cytoplasm and more nuclei), fibrosis, later lipomatosis

19. Duchenne-type dystrophy: X-linked recessive disorder – males affected only lack of dystrophin (immunohistochemistry) early childhood (5 years), pelvifemoral groups of muscles (frequent falls, gait disturbances, difficulty in rising), progress to other muscle groups (wheelchair bound between the ages of 10 to 12 years), death usually before the age of 20 years (respiratory difficulties, pneumonia) Becker-type dystrophy: similar to the Duchenne-type dystrophy, but much milder clinical picture dystrophin is produced, but is abnormal

20. Dystrophia myotonica: autosomal dominant disorder after the age of 20 years, sometimes congenital clinical features: myotonia (prolongation of muscle contraction after voluntary effort has ceased), muscle weakness (facial muscles, distal muscle groups) multisystemic disease: frontal baldness, cataract, cardiomyopathy, dementia, gonadal atrophy)

21. Myasthenia gravis acquired autoimmune disorder: autoantibodies against acetylcholine receptors on the motor endplate → defect of neuromuscular transmission hyperplasia of thymus (60%), thymoma (20%) Clinical features: abnormal muscle fatiguability, muscle weakness respiratory muscles may be severely affected (patients may need mechanical ventilation) Microscopic features: no light-microscopic abnormalities

22. Myositis (inflammation of muscles) bacterial, viral (complication of systemic infections) autoimmune myositis: dermatomyositis/polymyositis Trichinosis eating meat containing viable cysts of Trichinella spiralis (improperly cooked pork products) larvae released after ingestion, and penetrate into blood throught duodenal mucosa → dissemination throughout the body (lung, heart, brain, skeletal muscles) larvae enclosed within the membrane (parasitic cysts), calcification of dead cysts Myositis ossificans tumor-like lesion sometimes preceded by trauma must be distinguished from extraskeletal osteosarcoma central area of plump, mitotically active fibroblasts surrounded by zones of immature woven bone and mature lamellar bone