Fibrous Dysplasia: Management of the Optic Canal

Sir: In Dr. Satterwhite and colleagues’ article, “Fibrous Dysplasia: Management of the Optic Canal,”1 the authors reported their experience with prophylactic optic nerve decompression. Long-term visual compromise developed in two of five fibrous dysplasia patients undergoing therapeutic optic nerve decompression and one of seven patients undergoing prophylactic optic nerve decompression, with three of 12 (25 percent) having adverse outcomes. They concluded that fibrous dysplasia patients who underwent prophylactic optic nerve decompression had better outcomes, and that optic nerve unroofing is “safe in our [sic] hands.” We disagree with the authors’ belief that, “optic canal involvement is a predictor for impending optic nerve damage.” Our National Institutes of Health cohort2 reported 13 patients with optic neuropathy, of which 10 had growth hormone excess [seven of 13 (54 percent)] or associated aneurysmal bone cyst [three of 13 (23 percent)]. We know growth hormone excess in fibrous dysplasia is associated with macrocephaly and vision loss, with some patients developing blindness. Recent analysis of the National Institutes of Health cohort indicates that early diagnosis and treatment may prevent growth hormone excess–associated morbidity (specifically, vision loss).3 Furthermore, optic nerve decompression in symptomatic patients has been shown to have high perioperative morbidity. We advocate for close observation (i.e., frequent ophthalmologic examinations with optical coherence tomography and evoked potentials, and medical treatment of growth hormone excess when present) as the preferred approach to patients with fibrous dysplasia encasement of the optic canal. Thus, we feel that confounding factors such as untreated growth hormone excess and aneurysmal bone cysts, not long-term involvement of the optic canal, are predictors of visual compromise in the McCune-Albright population. This case series did not state whether patients had growth hormone excess or associated aneurysmal bone cyst. We stress the importance of a complete workup in fibrous dysplasia patients before surgery, because growth hormone excess can be treated nonoperatively, reducing the risk of optic neuropathy. Amit et al. performed a meta-analysis4 on patients from the National Institutes of Health: a total of 368 nerves were included in the meta-analysis; long-term follow-up revealed that surgery in asymptomatic patients is associated with worse prognosis compared with patients managed expectantly. Moreover, growth hormone excess was not found to have an association with optic neuropathy because young subjects with reported excess underwent early treatment. Visual loss was seen only in subjects whose growth hormone excess diagnosis and treatment were delayed until adulthood, as none of the subjects treated in childhood had visual disturbances.5 There is no evidence that fibrous dysplasia progression can be predicted, and it is not possible to foresee which patients would benefit from optic nerve decompression surgery. We agree that a randomized, prospective trial would be informative though difficult. Although the authors report a lower risk in prophylactic decompression at their center, they admit that, “Other authors have reported blindness with prophylactic unroofing, but in our hands, this never happened.” In light of the meta-analysis performed, it is unreasonable to create a standard of care based on the abilities of a few surgeons who have had rare complications. Furthermore, an outcome of three of 12 patients (25 percent) developing visual compromise is still relatively high. We strongly recommend against prophylactic optic nerve decompression based on the aforementioned meta-analysis data and our experience from the natural history protocol ongoing at the National Institutes of Health. DISCLOSURE The authors have no financial interest to declare in relation to the content of this communication. ACKNOWLEDGMENT This research was supported by the Intramural Research Program of the National Institutes of Dental and Craniofacial Research, National Institutes of Health. © copyright property of Intramural Research Program of the National Institutes of Dental and Craniofacial Research, National Institutes of Health. Andrea B. Burke, D.M.D., M.D.Alison M. Boyce, M.D.Michael T. Collins, M.D.Skeletal Clinical Studies SectionCraniofacial and Skeletal Diseases BranchNational Institutes of Dental and Craniofacial ResearchNational Institutes of HealthBethesda, Md.