RESUMO
PURPOSE: To determine whether an association exists between monoclonal gammopathy of undetermined significance (MGUS) and diffuse idiopathic skeletal hyperostosis (DISH). MATERIALS AND METHODS: Radiological studies of skeleton were performed in a series of 76 patients (51 males and 25 females) affected by MGUS, observed in a consecutive period of 36 months. They revealed hyperostotic lesions similar to those described in DISH. RESULTS: Patients affected by MGUS complicated by DISH were 35 (24 males and 11 females). The prevalence of skeletal hyperostosis (46%) appears higher than that reported by the literature in the general population (mean 15 %). Typically, the vertebral column is the predominant site of abnormalities in MGUS as well as in DISH: involvement of dorsal spine was observed in 16 males and 10 females; cervical spine in 12 males and 4 females, and lumbar in 9 males and 2 females. Peripheral ossifying enthesopathy ("whiskering" in the pelvis) was found in 7 cases, 5 males and 2 females. CONCLUSIONS: DISH is probably an ossifying diathesis of unknown aetiology; its occurrence in multiple myeloma and especially in MGUS is much higher because it is a fortuitous association. Many causes (accidental, dysmetabolic or degenerative) of DISH-like syndrome complicating dysgammaglobulinemias have been supposed, but at the present time this association remains a mere guess. A pathogenetic "event" responsible for hyperostosis may be supposed: in fact, in MGUS bone stimuli induced by osteoclast activating factor (OAF) and plasma cell proliferation -- even if lower than those observed in multiple myeloma -- are much more prolonged in time (see the slow progression of this condition, before it becomes symptomatic), so that the rate of calcium mobilized from skeleton and localized into soft tissues (i.e., tendons and ligaments) is higher. In this manner, the incidence of DISH-like ossification is higher than that observed in multiple myeloma and in the general population.
