Round # 10

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Diagnosis and Discussion

Correct Diagnosis: Monostotic Fibrous Dysplasia

Discussion:
Fibrous dysplasia is a rare disorder of skeletal development characterized by expanding fibro-osseous lesions. It is caused by an activating somatic mutation in the alpha subunit of the Gs protein, resulting in abnormal osteoblastic differentiation and increased bone turnover. It most commonly presents in the 2nd and 3rd decades of life, although it can first present in younger children as well. The lesions can affect one (monostotic) or many (polyostotic) bones, with a predilection for the long bones (femur, tibia, humerus) and calvarium. When polyostotic disease is associated with hyperpigmented caf-au-lait macules and precocious puberty or other endocrinopathies, the McCune-Albright syndrome is diagnosed.

Patients with monostotic disease are usually asymptomatic or complain of mild discomfort; those with more extensive disease are sometimes diagnosed when they sustain a fracture of an affected area. The monostotic variant is rarely progressive, and even less commonly undergoes malignant transformation. Laboratory anomalies are rare, except for modest chronic elevations in the alkaline phosphatase, reflective of increased bone turnover in the affected areas. Treatment of more severe lesions requires surgery for fracture management; more severe polyostotic disease has been treated with both IV and oral bisphosphonate therapy, although regression of lesions is rare.

References:

1. Schoenau E, Rauch F. Fibrous dysplasia. Horm Res 57(2):79-82, 2002.
2. Chapurlat RD, Meunier PJ. Fibrous dysplasia of bone. Baillieres Best Pract Res Clin Rheumatol 14(2):385-98,2000.
3. Resnick D. Tuberous Sclerosis, Neurofibromatosis, and Fibrous Dysplasia. In: Resnick D, ed. Diagnosis of Bone and Joint Disorders 3rd ed. Philadelphia, London, Toronto, Montreal, Sydney, Tokyo: Saunders, 4057-4070, 1995.
4. Chapurlat RD, Delmas PD, Liens D, Meunier PJ. Long-term effects of intravenous pamidronate in fibrous dysplasia of bone. J Bone Miner Res 12(10):1746-52, 1997.
5. Marie PJ. Cellular and molecular basis of fibrous dysplasia. Histol Histopathol 16(3):981-8, 2001.

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