Pathoma 3. Flashcards
achondroplasia
impaired cartilage proliferation in the growth plate; common cause of dwarfism
What causes achondroplasia?
AD activating mutation in fibroblast growth factor receptor 3 (FGFR3) - overexpression INHIBITS growth
What are clinical features of achondroplasia?
short extremities with normal sized head and chest (due to poor endochondral bone formation, but normal intramembranous bone formation)
Endochondral bone formation
formation of a cartilage matrix which is then replaced with bone (long bones)
Intramembranous bone formation
formation of bone without a preexisiting cartilage matrix
Osteogenesis imperfecta
congenital defect of bone formation resulting in structurally weak bone
What causes osteogenesis imperfecta?
AD defect in collagen type I synthesis
What are the clinical features of osteogenesis imperfecta?
multiple fractures of bone, blue sclera, hearing loss
Osteopetrosis
inherited defect of bone resorption resulting in abnormally thick, heavy bone that fractures easily (like chalk)
What is osteopetrosis the result of?
poor osteoclast function due to carbonic anhydrase II mutation (leads to loss of the acidic microenvironment required for bone resorption)
What are the clinical features of osteopetrosis?
bone fractures, anemia, thrombocytopenia, leukopenia with extra medullary hematopoiesis (due to bony replacement of the marrow), vision and hearing impairment, hydrocephalus (narrowing of foramen magnum), renal tubular acidosis (carbonic anhydrase II mutation)
What is the treatment for osteopetrosis?
bone marrow transplant because osteoclasts are derived from monocytes (need new monocytes)
Rickets/Osteomalacia
defective mineralization of osteoid (normally produced by osteoblasts)
What causes rickets/osteomalacia?
low levels of Vit D (causes low serum calcium and phosphate)
How is vit D activated?
by 25-hydroxylation by the liver followed by 1-alpha-hydroxylation by the proximal tubule cells of the kidney
How does active Vit D raise serum calcium and phosphate?
intestine (increase absorption), kidney (increase resorption), bone (increase resorption)
What can vit D deficiency be caused by?
decreased sun exposure, poor diet, malabsorption, liver failure, renal failure
How does rickets present?
in children - pigeon breast deformity (inward bending of the ribs), frontal bossing (enlarged forehead), rachitic rosary (osteoid deposition at the costochondral junction), bowing of legs
How does osteomalacia present?
in adults - inadequate mineralization = weak bone, decreased serum calcium, decreased serum phosphate (because low vit D), increased PTH (because low Ca2+), increased alkaline phosphatase
What is osteoporosis?
reduction in trabecular bone mass resulting in porous bone with an increased risk for fracture
What are the risk factors of osteoporosis?
peak bone mass (age 30) and rate of bone loss afterwards. based on weight bearing exercise, poor diet, decreased estrogen
What are the most common forms of osteoporosis?
senile and postmenopausal
How does osteoporosis present clinically?
bone pain and fractures in weight-bearing area, bone density on DEXA scan, serum calcium, phosphate, PTH, alkaline phosphatase are NORMAL
What presents clinically like osteoporosis? How are they distinguished?
osteomalacia - labs are normal in osteoporosis for calcium, phosphate, PTH, alkaline phosphatase
What is the treatment for osteoporosis?
exercise, vit D, calcium to limit bone loss, bisphosphonates to induce apoptosis of osteoclasts
What drug is contraindicated in osteoporosis?
glucocorticoids because they worsen osteoporosis
Paget disease of bone
imbalance between osteoclast and osteoblast function
What is the etiology of page disease of bone?
unknown, but maybe viral
Where is paget disease of bone typically localized to?
one or more bones, but does NOT involve entire skeleton
What are the three stages of page disease of bone?
- osteoclastic (start working without permission of osteoblasts (osteoblasts receive signal from PTH) 2. mixed osteoblastic-osteoclastic (osteoblasts lays down as quickly as possible to try and make up for out of control osteoclasts but makes weak bone) 3. osteoblastic
What does biopsy of paget disease of bone reveal?
mosaic pattern of lamellar bone
What are the clinical features of paget disease of bone?
bone pain, increasing hat size, hearing loss, lion-like facies, isolated elevated alkaline phosphatase
What is treatment for paget disease of bone?
calcitonin (inhibits osteoclast function - opposite of PTH) and bisphosphonates (induces apoptosis of osteoclasts)
Bisphosphonates in clinical treatment
induce apoptosis of osteoclasts
What are complications of paget disease of bone?
high-output cardiac failure (due to AV shunts in bone) and osteosarcoma
Osteomyelitis
infection of marrow and bone typically in children
What is cause of osteomyelitis?
bacterial via hematogenous spread
Where does osteomyelitis seed in children?
transient bacteremia seeds metaphysis (growth plate)
Where does osteomyelitis seed in adults?
open-wound bacteremia seeds epiphysis (rounded end of a long bone)
What are common causes of osteomyelitis?
staph aureus (most common), gonorrhoeae, salmonella, pseudomonas, pasteurella, mycobacterium tuberculosis
What are clinical features of osteomyelitis?
bone pain with systemic signs of infection (fever and leukocytosis), lytic focus (abscess) surround by sclerosis of bone on x-ray (sclerosis surrounding necrosis)
How is diagnosis of osteomyelitis made?
blood culture
What is avascular necrosis?
ischemic necrosis of bone and bone marrow
What are causes of avascular necrosis?
trauma or fracture (most common), steroids, sickle cell, caisson disease (gas emboli lodging in bone)
What are complications of avascular necrosis?
osteoathritis and fracture
Osteoma - what is it and where does it typically present?
benign tumor of bone - surface of facial bones
Osteoid Osteoma
benign tumor of osteoblasts surrounded by a rim of reactive bone
Who doe osteoid osteoma typically occur in?
young adults (
Where does osteoid osteoma typically present?
cortex of long bones (outside - usually diaphysis)
How does osteoid osteoma typically present?
bone pain that RESOLVES WITH ASPIRIN