Modulation of spinal deformities in patients with neurofibromatosis Type 1

Study Design. A consecutive case retrospective chart and radiographic revie w. Objectives. To determine the incidence of nine radiographic dystrophic feat ures acquired during the process of modulation, and to analyze the statisti cal correlation of these acquired dystrophic features with clinical progres sion of a spinal deformity. Summary of Background Data. In patients with neurofibromatosis, spinal defo rmities with seemingly few initial dystrophic features have shown a tendenc y to acquire dystrophic changes during long-term follow-up periods. Similar ly, deformities with dystrophic changes can acquire further dystrophic feat ures. This phenomenon is termed "modulation," a feature unique to spinal de formities in neurofibromatosis. These dystrophic changes may evolve slowly or aggressively, and may spread to other regions as well. Methods. A review was done of the clinical records, photographs, radiograph s, and other imaging studies of 457 patients referred between 1982 and 1995 with the diagnosis of neurofibromatosis Type 1. One hundred twenty-eight p atients were diagnosed with a spinal deformity. Ninety-one patients who had a complete set of clinical and radiographic data were included in the stud y. Location and type of curve as well as the extent of spinal deformity wer e studied for their effect on the tendency for modulation. Initial spinal r adiographs were analyzed for nine radiographic dystrophic features: rib pen ciling, vertebral rotation, posterior vertebral scalloping, anterior verteb ral scalloping, lateral vertebral scalloping, vertebral wedging, spindling of the transverse process, widened interpedicular distance, and enlarged in tervertebral foramina. Subsequent radiographs were analyzed critically for evolution, progression, or spread of these features. Correlation of acquisi tion in these dystrophic features with clinical progression in the spinal d eformity, as measured in increments of scoliosis and kyphosis, was analyzed . Results. In 81% of patients with spinal deformity diagnosed before 7 years of age and in 25% of patients with such a diagnosis after 7 years of age, e vidence of modulation was observed. Location, side, and extent of the defor mity and patient gender did not influence the propensity of the deformity t o modulate, Correlation of modulation with clinical progression of the defo rmity showed rib penciling to be the only singular factor statistically ,in fluencing risk of progression. Of the deformities that acquired three or mo re penciled ribs, 87% showed significant clinical progression. No other rad iographic dystrophic feature individually influenced progression. However,w hen three or more of the dystrophic skeletal features were acquired, the ri sk of progression reached statistical significance in 85% of patients. Conclusions, Spinal deformities in patients with neurofibromatosis 1 should be regarded as deformities in evolution. One should resist assigning these evolving deformities to either the dystrophic or nondystrophic end of the spectrum without considering the possibility of modulation across the spect rum. A spinal deformity that develops before 7 years of age should be follo wed closely for evolving dystrophic features (i.e., modulation). When a cur ve acquires either three penciled ribs or a combination of three dystrophic features, clinical progression is almost a certainty.