[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Conditions](https://durgical.com/en/conditions/) › Fibrous dysplasia of bone and McCune–Albright syndrome [Conditions](https://durgical.com/en/conditions/) · [Endocrinology](https://durgical.com/en/conditions/) # Fibrous dysplasia of bone and McCune–Albright syndrome Patches of bone are replaced by weak fibrous tissue, causing pain, deformity and fractures; with [skin](https://durgical.com/en/anatomy/skin/) spots and hormone excess it is McCune–Albright syndrome. Updated 2026-11-01 ## Structures involved Tap one to see what it is and open it in 3D. - [Femur](https://durgical.com/en/anatomy/femur/) - [Maxillae](https://durgical.com/en/anatomy/maxilla/) - [Tibia](https://durgical.com/en/anatomy/tibia/) - [Hip bone](https://durgical.com/en/anatomy/hip-bone/) - [Sphenoid bone](https://durgical.com/en/anatomy/sphenoid-bone/) - [Temporal bones](https://durgical.com/en/anatomy/temporal-bone/) - [Optic canal](https://durgical.com/en/anatomy/optic-canal/) - [Optic nerve](https://durgical.com/en/anatomy/optic-nerve/) - [Ribs (back part)](https://durgical.com/en/anatomy/ribs/) ## Why it happens - [Bone remodeling](https://durgical.com/en/physiology/bone-remodeling/) - [G protein-coupled receptors and cAMP](https://durgical.com/en/biochemistry/topics/g-protein-coupled-receptors-and-camp/) - [Bone tissue: cells, compact and spongy bone](https://durgical.com/en/histology/bone-tissue-cells-compact-and-spongy-bone/) ## What it is A non-inherited bone disorder in which areas of normal bone and marrow are replaced by fibrous tissue and poorly formed woven bone. It may affect one bone (monostotic) or many (polyostotic). McCune–Albright syndrome is the combination of fibrous dysplasia with café-au-lait skin patches and overactive endocrine glands, most classically precocious puberty. ## Who gets it Uncommon; usually recognised in childhood or early adulthood, with the monostotic form the most frequent. McCune–Albright syndrome is rare, estimated at 1 in 100,000 to 1 in 1,000,000 people. Sex, ancestry and geography do not change the risk. ## Causes - Somatic activating mutation in GNAS (the Gs-alpha protein) arising after conception - Mosaicism: only the cell lines carrying the mutation are affected, so the extent depends on how early it arose - Not inherited and not passed on to children ## Risk factors - No known modifiable or inherited risk factors ## Pathophysiology The GNAS mutation keeps adenylate cyclase switched on, raising cyclic AMP in affected cells. In bone, skeletal stem cells proliferate and differentiate poorly, so marrow is replaced by fibrous tissue with immature bone that bends and fractures. The lesions overproduce FGF23, which can cause renal phosphate wasting. The same constitutive signalling in skin melanocytes produces café-au-lait patches, and in endocrine glands causes autonomous hormone release (ovarian oestrogen, thyroid hormone, growth hormone, cortisol). ## Classification - Monostotic fibrous dysplasia (one bone; often rib, femur, [tibia](https://durgical.com/en/anatomy/tibia/) or craniofacial bones) - Polyostotic fibrous dysplasia (several bones, often on one side of the body) - McCune–Albright syndrome: fibrous dysplasia plus café-au-lait patches and/or hyperfunctioning endocrinopathy - Mazabraud syndrome: fibrous dysplasia with intramuscular myxomas ## Symptoms and signs - Bone pain, limp and fractures after minor trauma - Bowing of the femur with a shepherd's crook deformity of the proximal femur - Facial asymmetry, swelling of the jaw or forehead, dental crowding, nasal congestion - Café-au-lait patches with irregular "coast of Maine" borders, often on one side of the midline - Precocious puberty (vaginal bleeding or breast development in a young girl), features of hyperthyroidism, acromegaly or Cushing syndrome ## Red flags - New loss of vision or hearing with skull-base fibrous dysplasia ([optic canal](https://durgical.com/en/anatomy/optic-canal/) or auditory canal compression) - Rapid growth of a lesion with increasing pain (possible malignant change or aneurysmal bone cyst) - Neonatal Cushing syndrome in McCune–Albright syndrome - Hip pain and inability to bear weight (proximal femoral fracture) ## Diagnosis **Clinical** Pattern of bone lesions with or without café-au-lait patches and endocrine signs; growth and puberty assessment; vision and hearing tests when the skull is involved. **Tests** Serum phosphate, calcium, alkaline phosphatase and vitamin D; endocrine screening (TSH and free T4, growth hormone and IGF-1, prolactin, oestradiol or testosterone, cortisol). Biopsy and GNAS testing of affected tissue when the diagnosis is uncertain. **Imaging** Radiographs show expansile lesions with a "ground-glass" matrix and thin cortex; CT for craniofacial lesions; a bone scan maps the extent of disease. ## Differential diagnosis - Paget disease of bone - Neurofibromatosis type 1 (café-au-lait spots with smooth borders, bone dysplasia) - Non-ossifying fibroma and simple bone cyst - Ossifying fibroma of the jaw - Low-grade central osteosarcoma ## Goal of treatment Control pain, prevent and treat fractures and deformity, protect vision and hearing, correct phosphate wasting and treat every hormone excess, which also limits bone damage. ## Treatment **Medical** Bisphosphonates for bone pain; dental check before starting because of the jaw-healing risk. **Medical** Phosphate and active vitamin D for phosphate wasting; aromatase inhibitors or other agents for precocious puberty; antithyroid drugs or thyroidectomy, somatostatin analogues for growth hormone excess. **Surgical** Orthopaedic fixation of fractures and correction of deformity (for example, intramedullary nailing of the [femur](https://durgical.com/en/anatomy/femur/)); craniofacial surgery for deformity or nerve compression. **Rehabilitation** Physiotherapy to keep strength and range of motion. **Follow-up** Periodic endocrine, vision, hearing and bone surveillance in polyostotic disease and McCune–Albright syndrome. ## Complications - Recurrent fractures and progressive limb deformity - Scoliosis - Vision or hearing loss from skull-base involvement - Hypophosphataemic rickets or osteomalacia - Malignant transformation to sarcoma (rare, under 1%) ## Prognosis Monostotic disease usually has a good outlook, and lesions often become less active after puberty. Polyostotic disease and McCune–Albright syndrome carry more fractures and deformity, and outcome depends on controlling hormone excess and phosphate wasting. ## Test yourself Think of the answer, then tap the question to see it. ## Which gene is mutated in fibrous dysplasia and McCune–Albright syndrome, and why is it not inherited? GNAS; it is a somatic mosaic mutation that arises after conception. ## What is the classic triad of McCune–Albright syndrome? Polyostotic fibrous dysplasia, café-au-lait patches with irregular borders and precocious puberty (or other endocrine hyperfunction). ## What is the typical radiographic appearance of fibrous dysplasia? An expansile lesion with a ground-glass matrix and thin cortex. ## What deformity does fibrous dysplasia cause in the proximal femur? A shepherd's crook (coxa vara) deformity. ## Which substance overproduced by fibrous dysplasia lesions causes renal phosphate wasting? FGF23 (fibroblast growth factor 23). [Add to my cards (5)](https://durgical.app/estudiar/?add=/en/conditions/fibrous-dysplasia-of-bone-and-mccune-albright-syndrome/) ## Related conditions - [Paget disease of bone](https://durgical.com/en/conditions/paget-disease-of-bone/) - [Neurofibromatosis (types 1 and 2)](https://durgical.com/en/conditions/neurofibromatosis/) - [Osteosarcoma](https://durgical.com/en/conditions/osteosarcoma/) - [Acromegaly and gigantism](https://durgical.com/en/conditions/acromegaly-and-gigantism/) - [Cushing syndrome](https://durgical.com/en/conditions/cushing-syndrome/) - [Thyroid nodule](https://durgical.com/en/conditions/thyroid-nodule/) - [Hypophosphataemia](https://durgical.com/en/conditions/hypophosphataemia/) - [Rickets and osteomalacia](https://durgical.com/en/conditions/rickets-and-osteomalacia/) - [Femoral Neck Fracture](https://durgical.com/en/conditions/femoral-neck-fracture/) Educational information, not medical advice. For any symptom, see a health professional. Sources: [Fibrous Dysplasia Symptoms, Causes, & Risk Factors | NIAMS](https://www.niams.nih.gov/health-topics/fibrous-dysplasia) (National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), 2025); [Fibrous Dysplasia/McCune-Albright Syndrome](https://www.nidcr.nih.gov/health-info/fibrous-dysplasia-mccune-albright-syndrome) (National Institute of Dental and Craniofacial Research (NIDCR), 2025); [McCune-Albright syndrome: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/mccune-albright-syndrome/) (MedlinePlus Genetics (U.S. National Library of Medicine), 2025). [← All conditions](https://durgical.com/en/conditions/) ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/conditions/fibrous-dysplasia-of-bone-and-mccune-albright-syndrome/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/fibrous-dysplasia-of-bone-and-mccune-albright-syndrome/