SAT-739 - Monostotic Fibrous Dysplasia of Skull

Introduction:
Fibrous dysplasia (FD) is a skeletal disorder where normal lamellar bone is replaced by irregularly woven fibrous bone leading to bone deformities, pain and fractures. FD is caused due to postzygotic activating mutation in GNAS gene encoding Gs alpha protein causing elevated intracellular cAMP. FD can present as monostotic FD (MFD), polyostotic FD (PFD) or McCune-Albright syndrome (MAS), a condition with polyostotic FD, café-au-lait spots, precocious puberty and endocrinopathies. Here we present a case of monostotic fibrous dysplasia of the skull.


Case Report:
A 58-year-old African American male with hypertension and headaches for 30 years. He reports a history of skull lesion which was biopsied, but results were unknown. No hearing loss, vision changes, paresthesia or fragility fractures. CT head revealed two ground-glass lytic lesions in the posterior calvarium (right greater than left), temporal bone, clivus, and occipital condyles. Bone scan showed increased uptake in the right skull and right fifth rib consistent with fibrous dysplasia or Paget’s disease. Initial labs with elevated PSA 37.2 ng/dl. Subsequent, PET scan showed increased uptake in prostate, skull base and right fifth rib. Prostate biopsy confirmed high grade Gleason 8 prostate cancer which was treated with radiation and leuprolide. Biopsy of the rib lesion showed no evidence of carcinoma, Paget’s disease, or fibrous dysplasia. Bone turnover markers (elevated alkaline phosphatase 268 IU/L) were elevated. Skull biopsy was consistent with fibrous dysplasia. Vitamin D supplementation and therapy with zoledronic acid for pain are planned.


Discussion: MFD is the most common presentation and involves craniofacial bones, proximal femur and ribs. Most MFD lesions are incidentally discovered but can present with deformity, asymmetry, hearing or vision impairment, pathologic fracture, paresthesia or pain. FD is usually slow and indolent growing, however rapid progression and rarely malignant change to osteosarcoma have been reported. Typical CT/MRI are well-defined radiolucent medullary lesions with “ground glass” appearance and a peripheral sclerotic rim. Skeletal survey or Bone scan and endocrinopathy evaluation are done if PAF or MAS are suspected. Bone biopsy is warranted in atypical presentation or if malignancy is suspected.

Currently there are no FDA approved treatments for FD. Initial goals include optimizing bone mineralization, prevent fractures, treatment of pain and surgery for appropriate cases. Bisphosphonates (IV) are considered for persistent and severe pain that was resistant to other pain modalities.

Treatment of craniofacial FD(CFFD) needs multidisciplinary approach with goals to prevent function loss (hearing or vision impairment), reducing facial deformity and long-term morbidity. Any active disease with rapid growth, new pain, functional loss warrants surgical referral.

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