Thebonelosspredisposestomicrofracturesandsecondaryhemorrhagesthatelicitaninfluxofmacrophagesandaningrowthofreparativefibroustissue,creatingamassofreactivetissue,knownasabrowntumor (Fig.21.9 ).Thebrowncoloristheresultofthevascularity,hemorrhage,andhemosiderin.Theselesionsoftenundergocysticdegeneration.Thecombinationofincreasedbonecellactivity,peritrabecularfibrosis,andcysticbrowntumorsisthehallmarkofseverehyperparathyroidismandisknownasgeneralizedosteitisfibrosacystica.
Fig.21.8Hyperparathyroidismwithosteoclastsboringintothecenterofthetrabecularesemblingatraintrack(dissectingosteitis).
Fig.21.9Resectedrib,harboringanexpansilebrowntumoradjacenttothecostalcartilage.
As bone mass decreases, affected patients are increasingly susceptible to fractures, bone deformation, and joint problems. Osteitis fibrosa cystica is now rarely encountered because hyperparathyroidism is usually diagnosed on routine blood tests and treated at an early stage. Restoration of PTH levels to normal can completely reverse the bone changes. Secondary hyperparathyroidism is usually not as severe or as prolonged as primary hyperparathyroidism, hence the skeletal abnormalities tend to be milder.
Osteopeniaandosteoporosisrepresenthistologicallynormalbonethatisdecreasedinquantity.Inosteoporosisthebonelossissufficientlyseveretosignificantlyincreasetheriskoffracture.Thediseaseisverycommon,withmarkedmorbidityandmortalityfromfractures.Multiplefactorsincludingpeakbonemass,age,activity,genetics,nutrition,andhormonalinfluencescontributetoitspathogenesis.
Osteomalaciaischaracterizedbybonethatisinsufficientlymineralized.Inthedevelopingskeleton,themanifestationsarecharacterizedbyaconditionknownasrickets.
HyperparathyroidismarisesfromeitherautonomousorcompensatoryhypersecretionofPTHandcanleadtoosteoporosis,browntumors,andosteitisfibrosacystica.However,indevelopedcountries,whereearlydiagnosisisthenorm,thesemanifestationsarerarelyseen.
Paget disease is a condition of increased, but disordered and structurally unsound, bone. This unique skeletal disease can be divided into three sequential phases: (1) an initial osteolytic stage, (2) a mixed osteoclastic–osteoblastic stage, which ends with a predominance of osteoblastic activity and evolves into (3) a final burned-out quiescent osteosclerotic stage (
Fig. 21.10 http://ebooksmedicine.net 804CHAPTER 21 Bones, Joints, and Soft Tissue Tumors
Fig. 21.10 Diagrammatic representation of Paget disease of bone demonstrating the three phases in the evolution of the disease.
Paget disease usually begins in late adulthood. An estimated 1% of the U.S. population older than age 40 is affected. An intriguing aspect is the striking geographic variation in the prevalence. Paget disease is relatively common in whites in England, France, Austria, regions of Germany, Australia, New Zealand, and the United States. In contrast, the disease is rare in the native populations of Scandinavia, China, Japan, and Africa.