294-300 Clinical rheumatology, 1985, 4, N ~ 3 Insulin and new bone formation in diffuse idiopathic skeletal hyperostosis G.O. LITTLE JOHN, Monash University Department of Medicine, Rheumatology Unit, Prince Henry's Hopital, St. Kilda Road, Melbourne, Victoria, 3004, Australia. SUMMARY The tendency of patients with DISH towards obesity or an adult onset of diabetes has been reflected in marked hyperinsulinaemia following glucose challenge. It is hypothesized that insulin at prolonged and high physiologic levels promotes new bone growth, particularly in the entheseal regions. These areas are also subject to various mecha- nical forces. The resulting new bone produces the radiological changes which characterise DISH. Key words: Insulin, Hyperostosis, DISH, New Bone Formation. INTRODUCTION Diffuse idiopathic skeletal hyperostosis (DISH) [ankylosing hyperostosis/Forestier's disease] is a condition which is characterised by the presence of new bone formation. Us- ing strict diagnostic criteria (1) the preva- lence of marked spinal DISH is usually between 4 and 12O7o (1-4). However, lesser degrees of spinal new bone formation, typical of those seen in early DISH, occur in up to 30o7o of the subjects over 45 years of age (4). A spectrum of bone change is seen and in mild to moderate degrees this bony condition is common. The entheseal region is that area where li- gaments, tendons, joint capsule or annulus fibrosis fibres insert into bone. It is the ex- Received 13 December 1984, Revision - accepted 25 March 1985 Correspondence to: G.O. LITTLE JOHN, Monash University Department of Medicine, Rheuma- tology Unit, Prince Henry's Hospital, St. Kilda Road, Melbourne, Victoria, 3004, Australia. cessive and exuberant new bone growth in the entheseal regions which produces the characteristic spinal and extra spinal mani- festations of DISH (1). In the spine the radiological and histological changes of DISH are distinct from those of interver- tebral osteochondrosis (5,6) and spondylosis deformans (5,7) with lack of disc abnormali- ty, apophyseal or sacroiliac changes and the requirement of flowing anterior spinal bone linking four contiguous vertebral bodies (1). The peripheral entheseal changes have also been well documented (1,8). However, in addition to the entheseal new bone there is also generalised hyperostosis away from entheseal regions (1). This is prominent in the metacarpal heads, trochan- ters and deltoid tuberosities, among other areas (1). Hyperostosis Frontalis Interna may be seen (1,9,10). There is also an in- crease in the amount of normal bone with increased cortical thickness of tubular bones, tufting of the distal phalanges and increase in size of the sesamoid bones (11). Patients with DISH also have a marked ten- dency to form post-operative heterotopic