To determine the range and activity of the clinical and biological features of patients aged <40 with Paget's disease of bone.
A retrospective two centre study of 314 patients with Paget's disease of bone from two university hospitals. The disease was diagnosed by radiological, serum alkaline phosphatase (AP) levels, or clinical features, and bone scintigraphy in most patients. Demographic data, reason for diagnosis, bones affected, disease extent using Coutris' index, complications during progression, and disease activity using Renier's index were assessed. Patients over and under 40 were compared.
18/314 (5.7%) patients were diagnosed before the age of 40; median (SD) age was 35.4 (5.5) (range 18-40) and AP 555.6 (566.3) IU/l (range 70-1949). Coutris' extension index was 12.8 (10.5) and Renier's activity index 35.9 (31.9). Younger patients had more affected bones (p<0.05) than those aged >40, higher level of extension (p<0.05), higher AP value (p = 0.05), and greater incidence of thoracolumbar spine disease. Disease activity did not differ significantly between the groups.
Paget's disease diagnosed before the age of 40 is more extensive but not more active, with higher AP values than in those diagnosed after age 40.