Osteoporosis in longstanding acromegaly : characteristic changes of vertebral trabecular architecture and bone matrix composition

Although it is now 60 years after Erdheim's (1931) detailed description of vertebral alterations in severe acromegaly, it is still unclear whether osteoporosis is a consistent feature of acromegalic bone disease or not. We studied the vertebral trabecular bone of a 44-year-old woman who had suffered active acromegaly for more than 20 years, and compared it with 17 normal as well as 2 osteoporotic controls. Histomorphometry revealed a very low trabecular bone volume and thus documented the presence of osteoporosis. The mean trabecular plate thickness was strikingly increased in acromegaly (possibly caused in part by a low-dose fluoride treatment), whereas it was normal or reduced in the osteoporotic controls. The meticulous analysis showed islands of cartilaginous tissue in the core of the acromegalic trabeculae which were not present in any other sample. In these areas collagen II was detected by immunohistochemistry. Biochemical analysis revealed that collagen II accounted for 7% of the total collagenous matrix. The degree of hydroxylation of lysyl residues of collagen I was close to the average value of all control samples studied. Our data show that osteoporosis can occur in acromegaly and that it is characterized by unusual architectural and compositional features. These findings challenge the prevailing view that the matrix of osteoporotic bone always shows a normal composition.