Fibrous Dysplasia

Timothy C. Hain, MD • Page last modified: March 14, 2020

Main Points:

Fibrous dysplasia is an uncommon cause of ear disease. As of 2020, In our records at Chicago Dizziness and Hearing, we have only 4 diagnoses of FD out of approximately 30,000 cases.

Definition of FIbrous displasia

Fibrous dysplasia is a benign bone disease that occasionally causes cosmetic issues with the skull, mass effect, and occasionally is associated with systemic features as in the McCune-Albright syndrome (Mishra and Rout, 2018) . The McCune-Albright syndrome (MAS) is even rarer, classically defined by the triad of polyostotic fibrous dysplasia of bone, cafe-au-lait skin pigmentation, and precocious puberty. (Kabali et al, 2019). Although related with a genetic variant, fibrous dysplasia is not inherited. (Boyce et al, 1993).

Endocrinopathies include: Gonadotropin-independent precocious puberty resulting from recurrent ovarian cysts in girls and autonomous testosterone production in boys; Testicular lesions with or without associated gonadotropin-independent precocious puberty; Thyroid lesions with or without non-autoimmune hyperthyroidism; Growth hormone excess; FGF23-mediated phosphate wasting with or without hypophosphatemia in association with fibrous dysplasia; and Neonatal hypercortisolism.(Boyce et al, 1993)

Associations with Dizziness and Hearing loss:

About 1/20 persons with FD also have Chiari or Basilar impression (potential causes of dizziness). (Pan et al, 2018).

Hearing loss is common in persons with craniofacial FD. According to Boyce et al (2018): "Hearing loss in craniofacial FD is common and mild to moderate in most individuals. It typically arises from FD crowding of the ossicular chain and elongation of the IAC, whereas EAC stenosis and otic capsule invasion are less common causes."

Visual loss from optic nerve involvment can also occur in FD (Loewenstern et al, 2018).

Diagnosis of Fibrous Dysplasia

FD ground grlass

Expansion and replacement with a ground glass appearance of the right mastoid and clivus in a patient with fibrous dysplasia. This is an axial view of a CT scan.

 

FD sclerotic
Sclerotic area of bone in the frontal skull (white blotches). This is a CT scan. On the left is the sagittal, and on the right the coronal view.

 

According to Hocaoglu et al (2014), "Our patients are described as FD at CT imaging with the following findings: expansion, ground glass density, expansion and sclerosis, expansion with sclerosis and lytic appearance, expansion and lytic appearance, and only sclerosis. Expansion was the main feature which was seen with other findings (85%). The most common finding was ground glass density and the least appearance was expansion with lytic areas and only sclerosis."

According to Frisch et al (2015), in the temporal bone, ". A growing number of patients are diagnosed incidentally through imaging, and since most patients experience a benign course, the majority can be followed clinically without need for intervention".

Management of fibrous dysplasia:

According to Boyce et al (1993), This is a multisystem disease and management usually requires a multidisciplinary team of specialists. "Management focuses on optimizing function and minimizing morbidity related to fractures and deformity (including scoliosis). Precocious puberty. Treatment prevents bone age advancement and compromise of adult height. For girls, the aromatase inhibitor letrozole is used; for boys, treatment options are less well established. Thyroid disease. Methimazole effectively manages hyperthyroidism; however, because hyperthyroidism is persistent, thyroidectomy is common. Growth hormone excess. Medical therapy is the preferred first-line treatment; options include (alone or in combination) octreotide and the growth hormone receptor antagonist pegvisomant. Hypercortisolism. Treatment varies by the presentation of neonatal Cushing syndrome. Surveillance: FD/MAS. Monitor for the following: Infants: clinical signs of hypercortisolism. All children: growth acceleration and other clinical signs of precocious puberty and/or growth hormone excess. Children: Age <5 years: thyroid function abnormalities. With thyroid abnormalities on ultrasound examination but normal thyroid function: periodic monitoring of thyroid function. Males: testicular lesions (physical examination and testicular ultrasound). Individuals on: Pegvisomant: hepatotoxicity. Somatostatin analogs: signs and symptoms of gallbladder disease. Females: breast cancer (earlier than is recommended for the general population). FD: Periodic radiographs to monitor existing FD and development of new lesions. Periodic serum phosphorus (for development of hypophosphatemia) and 25-hydroxyvitamin D levels. Craniofacial FD: yearly vision and hearing evaluations; periodic skull CT; routine serum IGF-1 levels through young adulthood. Spine FD: close monitoring for progressive scoliosis. Agents/circumstances to avoid: Contact sports and other high-risk activities (when skeletal involvement is significant); prophylactic optic nerve decompression (in individuals with craniofacial FD); surgical removal of ovarian cysts; radiation therapy for treatment of FD; risk factors for malignancy (e.g., radiation exposure). "

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