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Musculoskeletal Pathology Part II Joints,
Tendons, Tendon Sheaths, Bursae Muscles
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Joint diseases Congenital defects Dysplasia
coxae congenita Trauma Degenerative
diseases Osteoarthritis Inflammation Infective
arthritis Lyme disease Tuberculous
arthritis Rheumatoid arthritis Gout Tumours Pigmen
ted villonodular synovitis
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Dysplasia coxae congenita Autosomal recessive
congenital disorder Hypoplasia of hip joint with
congenital subluxation or luxation Untreated may
lead to early secondary osteoarthritis
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Trauma Disruption of synovial membrane
bleeding into the join cavity (haemarthros) May
lead to organization of haematoma fibrous
adhaesions limiting joint movements or ankylosis
(join space replaced by metaplastic
bone) haemarthros often complicates disorders of
coagulation (haemophilia)
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Osteoarthritis The 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 known
associated event or disease causally related to
OA (congenital disorders, inflammation, trauma)
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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 may enter into
small defects in the bone lead to forming of
subchondral pseudocysts Bony outgrowths at the
margins of the articular cartilage (osteophytes)
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Infective arthritis Caused by bacteria
(Staphylococcus aureus, Neisseria
gonorrhoeae) Routes of infection Blood spread
(far the most common) Direct penetration
(trauma) 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 may cause severe damage of the
articular cartilage secondary osteoarthritis
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Lyme disease Caused by spirochaete Borrelia
burgdorferi transmitted to humans via tick
bites Affects many tissues skin, nervous system
heart, joints Three clinical stages 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 (occurs
months to years after the initial infection)
arthritis (large joints, similar to rheumatoid
arthritis), nervous system (encephalopathy), skin
(acrodermatitis chronica atrophicans Herxheimer)
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Tuberculous arthritis Age children, almost
always associated with infection due to
haematogeneous dissemination Site knee, hip,
elbow and ankle (in descending order of
frequency) Clinical features insidious
development of pain, swelling and limitation of
movement, other signs of inflammation mild or
absent Microscopic features synovial
hyperplasia, tuberculous granulomas in 90 of
cases, acid-fast bacilli seldom identified
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Rheumatoid arthritis Common multisystem
autoimmune disease Age and sex occurs three
times as commonly in premenopausal women as it
does in males Site small joints of the hands
and feet, knees, hips, involvement frequently
symmetrical Rheumatoid factor (IgM) positive in
95
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Morphology Inflammatory hyperplasia of synovial
membrane with increased vascularity, cellularity
and synovial fluid production Inflammatory
infiltrate composed of lymphocytes and plasma
cells, formation of lymphoid follicles Proliferat
ion of inflammed hypervascular granulation tissue
termed pannus leads to degradation of
underlying articular cartilage, loss of cartilage
followed by formation of fibrous adhesions which
severely limit joint movement, sometimes
formation of metaplastic bone (ankylosis), bone
adjacent to the pannus is porotic Deformities of
joints (ulnar deviation of the fingers) Periartic
ular rheumatoid nodules in 30 (central area of
fibrinoid necrosis surrounded by macrophages and
fibroblasts arranged in a palisaded
fashion) Complication secondary amyloidosis
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Variants of RA Juvenile rheumatoid arthritis
(JRA) individuals younger than 16 years, large
joints predominantly involved, rheumatoid factor
often negative Stills disease (systemic JRA)
fever, leucocytosis, enlargement of liver, spleen
and lymph nodes Feltys syndrome RA
splenomegaly neutropenia
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Gout Disorder of purine metabolism leading to
hyperuricaemia Peak incidence between 30 60
years, male preponderance Deposition of
monosodium urate crystals into articular
cartilage, synovial membrane and periarticular
soft tissues (tophi, tophaceous gout) Clinical
features 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 Microscopic features deposits of urate
crystals surrounded by mixed inflammatory
infiltrate and foreign body-type giant cells
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Pigmeted villonodular synovitis Despite its
misleading name almost certainly a benign tumour
rather than inflammatory condition Site knee
joint most frequently affected (80) Clinical
symptoms mild pain, swelling, tenderness Macrosc
opic features brown-coloured thickened synovium
thrown into small villous folds Microscopic
features diffuse proliferation of mononuclear
cells resembling histiocytes with different
number of osteoclast-like multinuclear giant
cells and abundant depositions of haemosiderin
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Diseases of tendons, tendon sheaths and
bursae Degenerative ganglion Inflammatory tendov
aginitis bursitis
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Ganglion Area of myxoid degeneration of
connective tissue of tendon sheath Most commonly
on the extensor surfaces of hand and
feet Morphology thin walled pseudocyst
containing mucoid fluid
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Tendovaginitis (inflammation of the tendon
sheath) May be 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)
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Bursitis Most frequently 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
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Diseases of skeletal muscle Muscle
atrophy Muscle dystrophy Myasthenia
gravis Inflammatory disorders (myositis)
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Muscle atrophy Generalized myalnutrition,
hypopituitarism, immobilisation Localized
immobilisation of one limb, denervation (trauma,
neuritis, poliomyelitis) Microscopic features
decrease in size of muscle fibers
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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
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Duchenne-type dystrophy X-linked recessive
disorder males affected only Lack of production
of the protein dystrophin (can be demonstrate by
immunohistochemistry) Appears in early childhood
(5 years), pelvifemoral groups of muscles
affected earliest (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
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Dystrophia myotonica Autosomal dominant
disorder Usually 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) Multisyste
mic disease frontal baldness, cataract,
cardiomyopathy, dementia, gonadal atrophy)
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Myasthenia gravis Acquired autoimmune disorder,
in which autoantibodies bind to acetylcholine
receptors on the motor endplate defect of
neuromuscular transmission Associated with
hyperplasia of thymus in 60 and with thymoma in
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fatiguability, muscle weakness respiratory
muscles may be severely affected (patients may
need mechanical ventilation) Microscopic
features no light-microscopic abnormalities
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Myositis (inflammation of muscles) Bacterial,
viral (complication of systemic
infections) Autoimmune myositis
dermatomyositis/polymyositis Trichinosis Caused
by eating meat containing viable cysts of
Trichinella spiralis (improperly cooked pork
products) After ingestion, larvae are released,
attach to the duodenal mucosa and penetrate into
blood dissemination throughout the body (lung,
heart, brain) and finally invade the skeletal
muscles Larvae are enclosed within the membrane
(parasitic cysts), calcification of dead
cysts Myositis ossificans tumor-like lesion
sometimes preceded by trauma central area of
plump, mitotically active fibroblasts surrounded
by zone of immature woven and mature lamellar
bone must be distinguished from extraskeletal
osteosarcoma