CH18 - Musculoskeletal Pathology Flashcards
What is achondroplasia?
Impaired cartilage proliferation in the growth plate
What is achondroplasia a common cause of?
dwarfism
What is achondroplasia due to?
an activating mutation in fibroblast growth factor receptor 3 (FGFR3) Autosomal dominant
What does the overexpression of FGFA3 do?
It inhibits growth
What are most mutations for achondroplasia?
they are sporadic and related to increased paternal age.
What are the clinical features for achondroplasia?
Short extremities with normal-sized head and chest?
In achondroplasia, why is there short extremities with normal-sized head and chest?
its due to poor endochondral bone formation; intramembranous bone formation is not affected.
How is endochondral bone formation characterized?
by formation of a cartilage matrix, which is then replaced by bone; it is the mechanism by which long bones grow.
How is intramembranous bone formation characterized?
by formation of bone without a preexisting cartilage matrix; it is the mechanism by which fiat bones (e.g., skull and rib cage) develop.
In achondroplasia, what aspects are not affected?
Mental function, life span, and fertility are not affected
What is osteogenesis imperfecta?
It?s a congenital defect of bone resorption resulting in structurally weak bone
What is osteogenesis imperfecta most commonly due to?
an autosomal dominant defect in collagen type 1 synthesis
What is blue sclera?
thinning of scleral collagen reveals underlying choroidal veins.
What are the clinical features for osteogenesis imperfecta?
1) Multiple fractures of bone (can mimic child abuse, but bruising is absent) 2) blue sclera?3) Hearing loss
Why is there hearing loss in osteogenesis imperfecta?
Bones of the middle ear easily fracture
What is osteoporosis?
inherited defect of bone resorption resulting in abnormally thick, heavy bone that fractures easily
What is osteoporosis due to?
Its due to poor osteoclast function
What is an example for the multiple genetic variants that exist for osteoporosis?
carbonic anhydrase II mutation leads to loss of the acidic microenvironment required for bone resorption
In osteoporosis, why is there anemia in osteoporosis?
It is due to bony replacement of the marrow (myelophthisic process)
What are the clinical features for osteoporosis?
1) Bone fractures 2) Anemia, thrombocytopenia, and leukopenia with extramedullar hematopoiesis 3) Vision and hearing impairment 4) hydrocephalus 5) renal tubular acidosis
In osteoporosis, why is there vision and hearing impairment?
due to impingement on cranial nerves
In osteoporosis, why is there renal tubular acidosis?
Its seen with carbonic anhydrase II mutation, a lack of carbonic anhydrase results in decreased tubular reabsorption of HCO3 leading to metabolic acidosis.
What is the treatment for osteoporosis?
It is bone marrow transplant; osteoclasts are derived from monocytes.
What do Ricketts and osteomalacia result in?
Defective mineralization of osteoid
What do osteoblasts normally produce?
Osteoid which is then mineralized with calcium and phosphate to form bone
What are Rickets and osteomalacia due to?
low levels of vitamin D, which results in low serum calcium and phosphate
What is vitamin D normally derived from?
the skin upon exposure to sunlight (85%) and from the diet (15%).
What does activation of Vitamin D require?
25-hydroxylation by the liver followed by 1-alphahydroxylatton by the proximal tubule cells of the kidney
What does active vitamin D do?
it raises serum calcium and phosphate
How does active Vitamin D raise serum calcium and phosphate?
by acting on the intestines, kidney and bone
What is the effect of active Vitamin D on the intestine?
It increases absorption of calcium and phosphate
What is the effect of active vitamin D on the kidney?
it increases reabsorption of calcium and phosphate
What is the effect of active vitamin D on bone?
It increases resorption of calcium and phosphate
In whom is vitamin D deficiency seen?
with decreased sun exposure (e.g.. northern latitudes), poor diet, malabsorption, liver failure, and renal failure.
What is Rickets due to?
due to low vitamin D in children, resulting in abnormal bone mineralization.
In whom does Rickets most commonly arise?
in children < 1 year of age
How do Rickets present?
1) Pigeon-breast deformity 2) Frontal bossing (enlarged lorehead) 3) Rachitic rosary 4) bowing of the legs may be seen in ambulating children
What is pigeon-breast deformity in Rickets?
It?s inward bending of the ribs with anterior protrusion of the sternum
What is the frontal bossing in Rickets due to?
The enlarged forehead is due to osteoid deposition on the skull
What is Rachitic rosary due to?
osteoid deposition at the costochondral junction
What is osteomalacia due to?
low vitamin D in adults.
What is seen in ostomalacia?
Inadequate mineralization which results in weak bone with an increased risk for fracture.
What are the laboratory findings for osteomalacia?
decreased serum calcium, decreased serum phosphate, increased PTH, and increased alkaline phosphatase
What is osteoporosis?
It?s a reduction in trabecular bone mass
What does osteoporosis result in?
porous bone with an increased risk for fracture
What is the risk of osteoporosis based on?
peak bone mass (attained in early adulthood) and rate of bone loss that follows thereafter
When is peak bone mass achieved?
by 30 years of age
What is peak bone mass based on?
it is based on (1) genetics (eg vitamin D receptor variants), (2) diet, and (3) exercise.
What happens to bone mass after age 30?
slightly less than 1% of bone mass is lost each year
What might cause bone mass to be lost more quickly (after age 30)?
with lack of weight-bearing exercise (eg space travel), poor diet, or decreased estrogen (e.g., menopause).
What are the most common forms of osteoporosis?
They are senile and postmenopausal.
What are the clinical features for osteoporosis?
Bone pain and fractures in weight-bearing areas such as the vertebrae (leads to loss of height and kyphosis), hip, and distal radius, Serum calcium, phosphate, PTH, and alkaline phosphatase are normal; labs help to exclude osteomalacia (which has a similar clinical presentation).
What must be excluded when osteoporosis is suspected? How is this done?
Osteomalacia and the labs help to exclude it
How is bone density measured?
using a DEXA scan
What is the treatment for osteoporosis?
- Exercise, vitamin D, and calcium?limit bone loss 2. Bisphosphonates?induce apoptosis of osteoclasts 3. Estrogen replacement therapy is debated (currently not recommended). 4. Glucocorticoids are contraindicated (worsen osteoporosis).
What is paget disease of bone due to?
Imbalance between osteoclast and osteoblast function
When is paget disease of bone usually seen?
in late adulthood (average age > 60 years)
What is the etiology for Paget disease of bone?
It is unknown; possibly viral
Is Paget disease of bone localized or systemic?
It?s a localized process involving one or more bones; does not involve the entire skeleton
What are the three distinct stages of Paget disease of bone?
(1) osteoclastic, (2) mixed osteoblastic-osteoclastic, and (3) osteoblastic.
What is the end result for paget disease of bone?
it is thick, sclerotic bone that fractures easily
What does biopsy for Paget disease of bone reveal?
a mosaic pattern of lamellar bone
What are the clinical features for Paget disease of bone?
1) bone pain 2) increasing hat size 3) hearing loss 4) lion like faces 5) isolated elevated alkaline phophatase
In Paget disease of bone, why is there bone pain?
Its due to microfractures
In Paget disease of bone why is there increasing hat size?
Skull is commonly affected.
In Paget disease of bone, why is there hearing loss?
impingement on cranial nerve
In Paget disease of bone, why is there lion-like facies?
involvement of craniofacial bones
In Paget disease of bone, why is there isolated elevated alkaline phosphatase?
most common cause of isolated elevated alkaline phosphatase in patients > 40 years old
What is the treatment for Paget disease of bone?
1) calcitonin 2) bisphosphonates
Why does calcitonin help in Paget disease of bone?
It inhibits osteoclast function
Why does bisphosphonates help in Paget disease of bone?
It induces apoptosis of osteoclasts
What are the complications for Paget disease of bone?
1) High-output cardiac failure?due to formation of AV shunts in bone 2) Osteosarcoma
Why is there high-output cardiac failure as a complication for Paget disease of bone?
Its due to formation of AV shunts in bone
What is osteomyelitis?
Infection of marrow and bone
In whom does osteomyelitis usually occur?
in children
What type of infection is most commonly involved in osteomyelitis?
bacterial
In osteomyelitis, why would it most commonly arise?
It arises via hematogenous spread
What happens in osteomyelitis in children?
Transient bacteremia (children) seeds metaphysis.
What happens in osteomyelitis in adults?
Open-wound bacteremia (adults) seeds epiphysis.
What are the causes for osteomyelitis?
1) Staphylococcus 2) Gonorrhoeae 3) Salmonella 4) Pseudomonas 5) Pasteurella 6) Mycobacterium tuberculosis
What bacteria is the most common cause of osteomyelitis?
Staphylococcus aureus (90% of cases)
What is the cause of osteomyelitis in sexually active young adults?
gonorrhoeae
What is the cause of osteomyelitis in sickle cell disease patients?
Salmonella
What is the cause of osteomyelitis in diabetics or IV drug abusers?
Pseudomonas
What is the cause of ostoemyelitis in associated with cat or dog bite/scratches
pasteurella
What is the cause of ostoemyelitis in that usually involves vertebrae (Pott disease)?
mycobacterium tuberculosis
What are the clinical features for osteomyelitis?
1) Bone pain with systemic signs of infection (e.g., fever and leukocytosis) 2) Lytic focus (abscess) surrounded by sclerosis of bone on x-ray
What is the lytic focus in osteomyelitis called?
Sequestrum
What is the sclerosis in osteomyelitis called?
involucrum
How is the diagnosis for osteomyelitis made?
by blood culture.
What is avascular (aseptic) necrosis?
Ischemic necrosis of bone and bone marrow
What are the causes for avascular (aseptic) necrosis?
trauma or fracture (most common), steroids, sickle cell anemia, and caisson disease.
What are major complications for avascular (aseptic) necrosis?
osteoarthritis and fracture are major complications.
What are the bone tumors?
Osteoma, osteoid osteoma, osteochondroma, osteosarcoma, giant cell tumor, ewing sarcoma, chondroma, chondrosarcoma, metastatic tumors
What is osteoma?
Benign tumor of bone
Where does osteoma most commonly arise?
arises on the surface of facial bones
What is osteoma associated with?
Gardner syndrome