Pathoma - 18 (MSK - Part 1)

eliot2014's version from 2016-01-21 20:27

Section 1

Question Answer
What is achondroplasiaimpaired cartilage proliferation in the growth plate. Causes dwarfism
Whats the defect in achondroplasia?ACTIVATING mutation in FGF receptor 3 --> overexpression of FGFR3 inhibits growth of cartilage
which type of bone formation is NOT affected in acondroplasia?intramembranous bone formation = head, facial bones, clavicles, rib cage
which type of bone formation is affected in achondroplasia?endochondral bone formation
type of bone formation WITHOUT preexisting cartilage matrixintramembranous bone formation
type of bone formation characterized by cartilage later replaced by boneendochondral bone formation = long bone grows
whats the defect in osteogenesis imperfecta?defect in Type I collagen synthesis
why do you see blue sclera in osteogenesis imperfecta?thinning of scleral collagen shows choroidal veins
how does osteogenesis imperfecta present?multiple fractures of bone, blue sclera, and hearing loss (because bone of middle ear easily fracture
what process is defected in osteopetrosis?defect in bone RESORPTION
what enzyme is mutated in osteopetrosis?carbonic anhydrase II mutation --> loss of acidic environment needed to resorb bone
explain why you get renal tubular acidosis with osteopetrosis?lack of carbonic anhydrase results in decreased renal tubular absorption of HCO3- and hence metabolic acidosis
how does osteopetrosis present?bone fractures; anemia, thrombocytopenia, and leukopenia with extramedullary hematopoiesis (due to replacement of the bone marrow); vision and hearing impairment due to impingement on cranial nerves; hydrocephalus due to narrowing of the foramen magnum; renal tubular acidosis
whats the tx of osteopetrosis?bone marrow transplant (osteoclasts are derived from monocytes - remember that osteoclasts are the macrophages of the bone)
What is rickets/osteomalaciadefective mineralization of osteoid
What cell makes osteoid?osteoblasts
presentation of ricketspigeon-breast deformity, frontal bossing (enlarged forehead due to osteoid deposition), rachitic rosary, bowing of the legs
osteomalacia lab tests (serum calcium, phosphate, pth, and alk phos)calcium and phosphate low, pth (low ca is a stimulus to release pth) and alk phos high (alkaline environment is needed to calicify osteoid)
name the 2 areas where vit D gets activatedactivation requires 25-hydroxylation in the LIVER. followed by 1-alpha hydroxylation in the renal PCT
why do pts with rickets get rachitic rosary?due to OSTEOID deposition at costochondral junction
child presents with pigeon breast deformity and frontal bossingrickets = vit D deficiency
what type of environment is needed to leech out calcium during resorptionacidic environment
what lab value is associated with osteoBLAST activity?increased ALKP --> ALKP creates alkaline environment which is crucial to lay down Ca+2 into osteoid

osteoblast marker = ALKP
osteoclast marker = TRAP and urianry hydroxyproline
why do you see increased ALKP in osteomalacia?bc osteoblasts are still producing osteoid which needs ALKALINE environment

Section 2

Question Answer
reduction in trabecular bone massosteoporosis
bone disorder a/w NORMAL lab values?osteoporosis
Clinical features of osteoporosisbone pain and fractures in weight bearing areas such as vertebrae (leads to loss of height and kyphosis), hip, and distal radius; low bone density on DEXA scan, normal ca pth phosphorus and alk phos values
Whats the MOA of bisphosphonates?induce apoptosis of osteoclasts = which is good for osteoporosis tx
how many bones are affected in pagets?one or more
bone disorder with isolated increase in ALKP only! pagets disease of the bone
pt presents with bone disorder causing increasing hat sizepagets disease of the bone
what are the three stages of pagets?osteoclastic, mixed osteoblastic-osteoclastic, osteoblastic
pagets on biopsymosaic pattern of lamellar bone
clinical features of pagetsbone pain due to microfractures, increasing hat size, hearing loss due to CN impingement, lion-like facies, isolated elevated alk phos
what are the 2 drugs of choice in the tx of pagets disease of the bone?calcitonin (inhibits osteoclast fxn) and bisphosphonates (induces osteoclast apoptosis)
What are the 2 complications a/w pagets disease?high output cardiac failure (due to formation of AV shunts in bone) and osteosarcoma
what cancer is associated with pagets disease of the bone?osteosarcoma = malignant tumor of osteoblasts (bc late stage of pagets dz is due to overactivation of osteoblasts)
what type of heart problem is associated with pagets disease of the bone?high output cardiac failure
what disease is characterized infection of marrow and bone in kids?osteomyelitis
what bacteria causes osteomyelitis in diabetics or IV drug users?pseudomonas
what bacteria causes osteomyelitis involving the vertebra?TB
X-RAY shows lytic abscess surrounded by sclerosis of boneosteomyelitis
transient bacteremia in children with osteomyelitis seeds?metaphysis
Transient bacteremia in ADULTS with osteomyelitis seeds to which part of the bone?epiphysis
Causes of avascular necrosistrauma, fracture, steroids, sickle cell anemia, and caisson disease
Complications of avascular necrosisosteoarthritis and fracture