The use of anterolateral bowing of the lower leg in the diagnostic criteria for neurofibromatosis type 1

Abstract

Neurofibromatosis type 1 is diagnosed clinically based on the presence of two of seven criteria developed by a panel of experts in 1987. The sixth criterion focuses on skeletal findings and is as follows: "A distinctive osseous lesion such as sphenoid dysplasia or thinning of long bone cortex, with or without pseudarthrosis." The wording for this criterion is misleading. In particular, "thinning of long bone cortex" is not the characteristic radiographic presentation, and no mention of long bone bowing is included. The distinctive clinical feature of long bone dysplasia in neurofibromatosis type 1 is anterolateral bowing of the lower leg (portion of the body delimited by the knee and ankle). The usual radiographic findings of long bone dysplasia in neurofibromatosis type 1 at first presentation, prior to fracture, are anterolateral bowing with medullary canal narrowing and cortical thickening at the apex of the bowing. We suggest that anterolateral bowing of the lower leg, with or without fracture or pseudarthrosis, is a more appropriate description of the primary finding that a clinician will use to fulfill the sixth diagnostic criterion for neurofibromatosis type 1. Clarification of this diagnostic criterion is important for the clinician and for research protocols. Appropriate interpretation will improve understanding of the natural history and pathophysiology of neurofibromatosis type 1. Genet Med 2007:9(7):409-412.

Analysis of Radiographic Characteristics of Anterolateral Bowing of the Leg Before Fracture in Neurofibromatosis Type 1

“…Based on our previous clinical experience, NF1 individuals with anterolateral bowing of the lower leg prior to fracture have medullary canal narrowing with cortical thickening 6. Our retrospective radiographic review confirmed the appearance of cortical thickening with medullary canal narrowing near the apex of the bowing most consistently located near the junction of the middle and distal thirds of the tibia on plain films.…”

“…The NF1 diagnostic criterion for the skeletal abnormalities states: “A distinctive osseous lesion such as sphenoid dysplasia or thinning of long bone cortex, with or without pseudarthrosis.”2,3 Our anecdotal clinical experience is that cortical thinning was not a consistent component of tibial dysplasia in NF1 6. This prompted us to systematically investigate our clinical suspicions and better characterize the geometry of the tibia and fibula in individuals with NF1 with anterolateral bowing of the lower leg.…”

The Neurofibromatoses: Classification, Clinical Features and Genetic Counselling

“…The majority of reported children have been born into known HNPCC families. As a result of their studies of long bone dysplasias in NF1 Stevenson et al [33] have recently suggested alteration to the wording of criterion 6 of the NIH criteria and I have included this in the revised criteria (table 3).…”

Tibial geometry in individuals with neurofibromatosis type 1 without anterolateral bowing of the lower leg using peripheral quantitative computed tomography

“…Other osseous abnormalities are also observed and include short stature for familial background, bone overgrowth, bone cysts, increased dental caries, osteopenia, and non-dystrophic scoliosis. The skeletal abnormalities are a key component in the clinical diagnosis of individuals with NF1 [6–8], and skeletal abnormalities taken as a whole are quite common in NF1 [5]. …”