Adult PD of bone is the second commonest metabolic bone condition after 
osteoporosis. The condition is characterized by increased bone cell activity, 
with bone-resorbing osteoclasts often larger and containing more nuclei than 
normal, and osteoblasts producing increased amounts of disorganized bone. This 
leads to expanded bone of poor quality possessing both sclerotic and lytic 
areas. PD of bone has a strong genetic element, with a family history being 
noted in 10-20% of cases. A number of genetic defects have been found to be 
associated with the condition. The most common disease-associated variants 
identified affect the SQSTM1 gene, providing insights into disease aetiology, 
with the clinical value of knowledge of SQSTM1 mutation status currently under 
active investigation. The diagnosis may be suggested by an isolated raised total 
ALP without other identifiable causes. This can be confirmed on plain X-rays and 
the extent determined by isotope bone scan. The mainstays of treatment are the 
bisphosphonates, especially i.v. zoledronate, which results in long-term 
suppression of bone turnover. ALP is the usual means of monitoring the 
condition, although more specific bone turnover markers can be helpful, 
especially in coincident liver disease. Patients should be followed up to 
monitor for biochemical relapse or development of complications, which may 
require medical or surgical intervention.