The radiographs and histology are consistent with Paget disease, which is initially caused by increased osteoclastic bone resorption, and followed by an increase in bone formation through osteoblast activity.
Paget disease of the bone is a disorder of bone remodeling characterized by rapid bone turnover. The excessive bone resorption and bone formation disrupt normal bone architecture and lead to various complications such as bone pain, osteoarthritis, pathological fracture, bone deformity, deafness, and nerve compression syndromes.
Schneider et al. describe Paget disease, also known as osteitis deformans, as a nonmalignant disease. The origin of the disease remains unknown and many patients are frequently asymptomatic. However, symptomatic individuals most commonly present with pain over the affected bone. Diagnosis is primarily made by radiographs. Bisphosphonates are the most common treatment.
Delmas et al. review the use of total alkaline phosphatase as a serum marker for monitoring the activity of Paget disease. The authors report that bone specific alkaline phosphatase has the greatest sensitivity in Paget disease.
Figure A shows the skull with areas of lysis, areas of sclerosis (‘cotton-wool spots’), and calvarial thickening.
Figure B demonstrates coarsened trabeculae, cortical thickening, and enlargement of the left femur.
Figure C is a histologic slide showing abnormal bone formation with a mosaic pattern of woven bone and irregular sections of thickened trabecular bone and numerous cement lines.
Answer 1: While osteoblasts are involved in the pathogenesis of Paget disease, the primary disturbance is an exaggeration of osteoclastic bone resorption.
Answers 3-5: None of these cells are implicated in the primary disturbance causing Paget disease.
Schneider D, Hofmann MT, Peterson JA. Diagnosis and treatment of Paget's disease of bone. Am Fam Physician. 2002 May 15;65(10):2069-72. Review. PubMed PMID: 12046775.
PMID: 12046775 (Link to Abstract)
Delmas PD. Biochemical markers of bone turnover in Paget's disease of bone. J Bone Miner Res. 1999 Oct;14 Suppl 2:66-9. Review. PubMed PMID: 10510216.
PMID:10510216 (Link to Abstract)
USMLE World Step 1 QBank Question #987. Copyright © USMLEWorld, LLC 2012