NF1: Associated Bony Abnormalities

The osseous abnormalities classically associated with NF1 include long bone dysplasia, scoliosis, and sphenoid wing dysplasia. Other osseous findings include short stature (compared to familial background), bone cysts, and relative macrocephaly. Of NF1 individuals, approximately 1/3 have one or more orthopedic findings. [Crawford: 1999]
Long bone dysplasia is seen in 5% of NF1 individuals and classically involves the tibia (though Involvement of other long bones has been reported), with fibular involvement seen in 43% of those with long bone dysplasia. The typical presentation is anterior lateral bowing leading to fracture and non-union or pseudarthrosis. Tibial pseudarthrosis is strongly associated with NF1 – 50% of individuals with tibial pseudarthrosis have NF1. The bowing usually presents before 4 years of age and fractures have been seen in utero. Before 2 years of age, 53% of NF1 individuals with long bone bowing will experience a fracture. [Stevenson: 1999] The extremities (particularly the lower leg) of children with NF1 should be carefully examined for any anterior-lateral bowing. If bowing is evident, an x-ray and referral to orthopedics should be made. Bracing should then be initiated if fracture has not yet occurred. Treatment of pseudarthrosis is controversial and studies are underway to determine the clinical outcome and long-term treatment results of this complication.
Both idiopathic and dystrophic forms of scoliosis are seen in individuals with NF1 (combined 10-33%), with a typical onset between 7-16 years. [Vitale: 2002] The dystrophic form is defined by one of the following dystrophic osseous finding: spinal canal widening, vertebral body narrowing, rib-penciling, vertebral wedging, defective pedicles, and vertebral scalloping. The non-dystrophic form of scoliosis is more common in children with NF1 [Vitale: 2002], but dystrophic scoliosis (typical presenting with a sharply angulated curve) is progressively debilitating and requires a more aggressive approach, with surgical intervention sooner. Every child with NF1 should be screened for scoliosis and any suspicion should prompt a PA and lateral erect thoracolumbar spine image. Referral to orthopedics is indicated if scoliosis is evident.
Sphenoid wing dysplasia is a congenital abnormality seen in approximately 7-11% of NF1 patients. [Friedman: 1997]; [Young: 2002] It is always unilateral, and approximately 50% will have a clinically apparent plexiform neurofibroma of the temporal-orbital region. One should have a lower index of suspicion for facial plexiforms in individuals with sphenoid wing dysplasia, and they may benefit from earlier imaging by MRI. Exophthalmosis is a rare complication that may require intervention, but the sphenoid wing dysplasia usually does not cause significant clinical complications or require therapeutic management.

Authors & Reviewers

Current Authors and Reviewers:
Author: David A. Stevenson, MD
Reviewers: Karin Dent, MS, CGC
David Viskochil, MD, Ph.D.

Page Bibliography

Crawford AH, Schorry EK.
Neurofibromatosis in children: the role of the orthopaedist.
J Am Acad Orthop Surg. 1999;7(4):217-230. PubMed abstract
Excellent review of the orthopedic manifestations of NF1 particularly for orthopedic physicians managing NF1 patients.

Friedman JM, Birch PH.
Type 1 neurofibromatosis: a descriptive analysis of the disorder in 1,728 patients.
Am J Med Genet. 1997;70(2):138-143. PubMed abstract
A large case series utilizing an international database; authors are international authorities on clinical aspects of NF1. Excellent review, focused on clinical characteristics and natural history.

Stevenson DA, Birch PH, Friedman JM, Viskochil DH, Balestrazzi P, Boni S, Buske A, Korf BR, Niimura M, Pivnick EK, Schorry EK, Short MP, Tenconi R, Tonsgard JH, Carey JC.
Descriptive analysis of tibial pseudarthrosis in patients with neurofibromatosis 1.
Am J Med Genet. 1999;84(5):413-419. PubMed abstract
One of the largest case series, through a multi-center, international collaboration, of tibial pseudarthrosis in NF1 describing the natural history and presentation of this hard to treat complication of NF1.

Vitale MG, Guha A, Skaggs DL.
Orthopaedic manifestations of neurofibromatosis in children: an update.
Clin Orthop. 2002(401):107-118. PubMed abstract
A recent review of the orthopedic manifestations of NF1. Very well organized and informative.

Young H, Hyman S, North K.
Neurofibromatosis 1: clinical review and exceptions to the rules.
J Child Neurol. 2002;17(8):613-621. PubMed abstract
Concise, up to date, review of clinical aspects of NF1 with focus on unusual manifestations.