PAINDYS_Characterizing Pain in Fibrous Dysplasia of Bone/McCune-Albright Syndrome: an Exploratory Pilot Study

Plain-language summary

Fibrous dysplasia of bone (FD) / McCune-Albright syndrome (MAS) is a rare congenital bone disorder affecting one or multiple bones, caused by a mosaic somatic mutation of the GNAS gene. In some cases, it may be associated with endocrine or cutaneous abnormalities. The spectrum of bone disease is broad, ranging from isolated monostotic fibrous dysplasia to complete skeletal involvement. Functional prognosis can be complex due to pain, bone deformities, and fracture risk. The disease may initially be identified through non-specific clinical signs such as pain. Indeed, bone pain has been reported in up to 81% of adults and 49% of children, mainly affecting the lower limbs and the spine, with highly variable pain intensity that does not always correlate with the extent of bone lesions. This pain may persist throughout life and impact patients' daily activities. In the general population, it is well known that chronic musculoskeletal pain following events such as surgery or fractures can be associated with central sensitization, a neurophysiological phenomenon characterized by hyperreactivity of the central nervous system, along with impaired modulation of pain through descending inhibitory pathways, a normally protective mechanism that becomes reduced. The pathophysiology of bone pain in FD/MAS remains poorly studied and poorly understood. The presence of central sensitization, reduced pain modulation, and hypersensitivity to everyday stimuli are rarely described but suggested by the existence of chronic pain often lasting many years. The mixed characteristics of pain experienced (nociceptive, neuropathic, inflammatory, or nociplastic) are also poorly defined. To date, no study has explored pain in FD/MAS using a psychophysical approach in comparison with a control population. Our hypothesis is that patients with FD/MAS exhibit central sensitization with reduced pain modulation. This exploratory pilot study aims to investigate, through psychophysical approaches, the pathophysiological mechanisms underlying pain in FD/MAS.

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