Metabolic Disorders Flashcards
When does peak bone density generally occur?
25-35 years
What factors contribute to higher peak bone density?
- M>F
- ethnicity/genetics (African American)
- ^activity
- nutrition (vit D, phosphorus, Ca)
- hormones (estrogen = protective)
Name 2 potential causes of decreased bone synthesis leading to decreased bone density
- decreased osteoblastic function: organic to inorganic ratio is maintained
- decreased ability to make collagen with age, so less organic material to mineralize
Name a potential cause of decreased mineralization of osteoid leading to decreased bone density
lack of vit D or Ca2+ (osteomalacia, hyperparathyroidism), organic to inorganic ratio changes
Name a potential cause of increased bone destruction leading to decreased bone density
balance of osteoclastic and osteoblastic activity shifts
How does normal bone remodeling compare to that of elderly people?
- normal: same amount of bone before & after cutting cone
- elderly: net loss of bone
What condition in when the body’s bones become weak and break easily?
Osteoporosis
How does the organic to inorganic ratio change with osteoporosis?
Normal for age
(quality normal, quantity decreased)
What is the vitamin D deficiency which results in the abnormal softening of bone that occurs in adults?
Osteomalacia
In osteomalacia, bone quality is ____ and quantity may be ____
decreased
decreased
(bones soften AND weaken)
How does the organic to inorganic ratio change with osteomalacia?
increased
(bone mass also decreased)
What type of osteoporosis is characterized by a change in osteoclastic:osteoblastic balance?
Primary Osteoporosis
What is type 1 primary osteoporosis?
post-menopausal (exclusively females)
- estrogen drop increases osteoclastic activity
What is Type 2 primary osteoporosis?
Senile osteoporosis
- age related change of osteoblastic function
What hormone plays a major role in the regulation of bone remodeling in both men and women?
Estrogen
What physiological event poses a major risk for osteoporosis?
Menopause
How does estrogen act to maintain bone density?
- blocks RANKL, suppressing osteoclastic activity
- inhibits osteoblast apoptosis -> increases osteoblast lifespan
- decreases production of bone-resorbing cytokines
How does hormone replacement therapy (HRT) work on bone modeling?
- estrogens given to post-menopausal women
- ^calcitriol (tries to ^Ca)
- ^Ca absorption
- slows loss, does not contribute to rebuilding
What category of drugs is advertised to help with bone density?
bisphosphonates (eg. Boneva)
How do bisphosphonates help with bone density?
decrease osteoclastic activity (does NOT increase deposition
What laboratory values would you be expect to see in a patient with osteoporosis?
All normal (slow process, no inflammation indicated)
Name 5 potential causes of secondary osteoporosis
- disuse
- endocrine & genetic abnormalities or malabsorption issues
- chronic corticosteroid Rx
- multiple myeloma
- complex regional pain syndrome
Name 3 common areas of fracture in osteoporosis
- hip
- spine
- distal radius
What % bone loss is necessary before visible radiographically?
30-50%
What tool is used to quantify severity of bone density loss?
DEXA scan
What is the T-score on a DEXA scan?
- bone density compared with 18-25y/o of same race & sex
- gives fracture risk
What is the Z-score on a DEXA scan?
bone density compared with people of same age, race, sex
(useful for pre-menopausal evaluation of density)
A T-score of +1 to -1 is considered ____
normal
A T-score of -1 to -2.5 is considered ____
osteopenia
A T-score of -2.5 or less is considered ____
osteoporosis
A T-score of -2.5 or less, with a history of fragility fracture is considered ____
severe osteoporosis
What are the fracture risks for T-scores of -2, -3, and -4?
-2 = 4x more likely
-3 = 8x
-4 = 16x
Decreased bone density on x-ray is called ____
osteopenia
In a patient with osteoporosis, the nucleus pulposus can break vertebral endplates causing a ____ appearance
bi-concave (AKA cod fish)
What kind of fracture occurs at the distal radius and is usually do to falling on an outstretched hand?
Colles Fracture
What terms describes the osteoporotic hyperkyphosis caused by multiple compression fractures?
Dowager’s Hump
What Vitamin D deficiency results in the abnormal softening of bone leading to bowing of the legs in children?
Rickets
Are the bone changes due to rickets generally reversible or irreversible?
Irreversible
name 3 sources of acquired vitamin D deficiency
- inadequate sun
- inadequate dietary intake
- decreased absorption
What is vitamin D-dependent Rickets type I?
defective hydroxylation of metabolites in liver or kidney
What is vitamin D-dependent Rickets type II?
end organ insensitivity to vitamin D
What affects does Vitamin D deficiency have on the body?
- decreased calbindin production –> decreased GI absorption of Ca2+ and PO4
- lower plasma Ca2+ levels –> ^PTH secretion
- lower calcitriol (active vit D) –> less Ca2+ retrieved from bone
- phosphate excreted in urine, Ca2+ retained
- Long term: hypophosphatemia and modest decrease Ca2+
What is the net effect of vitamin D deficiency on the body?
decrease in bone mineralization
(excessive osteoid accumulates and is not well mineralized due to low Ca and Phosphate)
Describe the diagnostic profile of vitamin D-dependent rickets type I
- slightly reduced plasma Ca
- greatly reduced plasma phosphate
- elevated PTH
- increased alkaline phosphatase
What are some of the clinical manifestations of Osteomalacia?
- no symptoms early, eventual dull, aching bone pain
- lower back, pelvis, hips, legs ribs
- pain may worsen at night or wt. bearing
- muscle weakness
- patients adopt waddling gait due to decreased muscle tone and leg weakness
What radiographic finding consists of unmineralized osteoid seams which appear as a hazy, indistinct, dark line with callous formation?
Pseudofracture
What are the radiographic findings in osteomalacia?
- generalized osteopenia
- pseudofractures
- corticomedullary indistinction
- no/minimal deformity (reversible)
What are the characteristics of Rickets?
- more severe consequences
- irreversible growth impacts (bow-leg)
- bilateral
- lack of control of endplate growth (decreased cartilage formation & osteoid mineralization)
What are the radiographic findings of Rickets?
- generalized osteopenia
- widened growth plates (paintbrush metaphysis)
- bowing of wt. bearing bones
- pseudofractures
- discontinuities due to buckling, tearing of bone
What type of bone deformity will weight bearing bones and ribs undergo in patients with Rickets?
Genu varum
Name 2 clinical signs of Rickets
- hypotonia
- waddling gait
What conditions is characterized by the excessive sensitivity to Vitamin D?
Hypervitaminosis D
What is the most common reason for Hypervitaminosis D?
Over supplementation
excessive sensitivity to vitamin D is called ____
sarcoidosis
What are some clinical manifestations of Hypervitaminosis D?
- hypercalcemia
- ^urinary Ca excretion
- nephrolithiasis
- nephrocalcinosis
- metastatic calcifications
What are some of the generalized signs and symptoms of Hypercalcemia?
- Dulled mentation
- Headaches
- Muscle weakness and hyporeflexia
- Lethargy
- Generalized musculoskeletal pain
- Anorexia
- Constipation
What lab results would you expect to see in patients with Hypervitaminosis D?
- Decreased PTH
- Increased serum and urinary calcium levels
vitamin C is an important cofactor in the hydroxylation of ____ and ____
proline & lysine
What happens to collagen in a patient with scurvy?
- collagen lacks tensile strength
- changes in collagen synthesis –> reduced osteoblastic function –> decreased bone density
What are some of the clinical manifestations of Scurvy?
- Increased hemorrhage (vessel fragility)
- Subperiosteal bleeding
- Petechial hemorrhages, ecchymosis & purpura
- Swollen, bleeding gums
- Impaired bone growth
- Joint & muscle pain
- Delayed/impaired wound healing
What are the radiographic findings of scurvy?
- generalized osteopenia
- white line of Frankel
- Wimberger’s ring
- Pelkin’s spurs
- Trummerfeld zone
- subperiosteal hemorrhage
Extra deposition on the metaphyseal side of the growth plate is called ____
white line of Frankel
