Fibrous dysplasia is a monostotic or polyostotic bone growth disorder caused by mosaicism involving the mesenchymal tissue. The presenting signs include pain and spontaneous fractures. Last year, Meneses et al. described a case in this journal1 and, in this letter, we report another.

A year ago, a 36-year-old man was referred to us with pain and a significant increase in his alkaline phosphatase levels: 658U/l (normal range: 40–130). He had never been examined by a rheumatologist, despite the fact that he had been diagnosed as having polyostotic fibrous dysplasia at the age of 5 years. He had undergone cranioplasty twice for cranial volume reduction and decompression surgery on another 2 occasions to relieve pressure on the left optic nerve. He had had a clavicular fracture and, shortly before our first encounter, fracture of left femur, without previous trauma, but with the fracture line over preexisting osseous cystic lesions. The examination revealed a head circumference of 67cm, hypertelorism and thoracolumbar scoliosis, with a lump in left costal region that was painful on palpation. Moreover, he presented with right-sided coxa vara and leg length discrepancy. The patient was treated with pamidronate (180mg/iv every 6 months), which relieved his symptoms and reduced his alkaline phosphatase level by over 20% to 390 U/l.

This disease is caused by a point mutation (activation of the GNAS1 gene) in part of the bone tissue.2,3 It is characterized by the coexistence of cells having the genetic alteration and normal cells (mosaicism). This mutation induces an expansion of osteoprogenitor cells and their accumulation in the bone marrow spaces, provoking localized hematopoietic tissue loss and bone marrow fibrosis. The collagen shows changes in orientation and biochemical composition. Markers of bone remodeling may be elevated, as occurred in our patient. It is usually asymptomatic and the diagnosis is incidental, although there may be pain, swelling, deformity and/or neurological involvement. Seventy percent of the cases are diagnosed before the age of 30 years.4 The dysplastic tissue is highly vascularized, and is prone to spontaneous bleeding with subsequent cyst formation. The bones widen and the cortical bone thins, and spontaneous fractures can occur as a complication when the condition affects weight-bearing long bones. The presence of intralesional cystic lesions measuring over 2.5cm in diameter increases the risk.5

It can affect several adjoining cranial bones, obliterating the sutures, compress cranial nerve pairs at their exit or affect structures of the middle ear.

The changes observed in plain radiography are variable, depending on the proportion of osseous and fibrous components of the lesion and on its location.

Treatment depends on the presenting signs, and ranges from a wait and see attitude, curettage of the lesions, correction of the deformities and nerve decompression,5 to treatment with bisphosphonates in polyostotic forms with active bone remodeling markers. In the monostotic forms, complete ablation of the lesion prevents recurrence. The rate of recurrences after curettage and grafting is high, especially in children. Thus, its use on a routine basis is not recommended, and it is reserved for the decompression of nerve structures.

To this day, there is no curative treatment for this disease. Uncontrolled studies have demonstrated the utility of pamidronate,6 which improves even the radiological changes and the physical aspect of the patient,7 basically when the facial skeleton is affected. The use of bisphosphonates has been shown to reduce the painful symptoms, with a decrease in remodeling markers and an increase in bone mineral density, and even results in the filling of cysts and cortex thickening.8 In another study, a reduced incidence of fractures was observed.9

A pediatric patient treated with denosumab because of the inefficacy of the bisphosphonates developed severe secondary effects.10

Chemotherapy and radiotherapy are not effective, and the latter can facilitate fractures and predispose the patient, albeit rarely (0.4%), to malignant transformation.4

We consider notable the delay in the referral of this patient to our department, despite the elevation of his alkaline phosphatase levels and his pain, a circumstance that suggests a lack of knowledge of the possibility of using beneficial drug therapies. The physicians who may at some time treat these patients should be aware of the risk of secondary fractures in weight-bearing bones when cystic lesions greater than 2.5cm in diameter are observed.4