Neural Growth Factor ( NGF) Receptor Expression in Human Cross-Facial Nerve Grafts: A Contributor to Good Functional Outcome

Unpredictable functional outcomes after microneurovascular reconstruction of facial paralysis call for attention to the phenomena taking place at the tissue level. In biopsies of the target organ, microneurovascular mucle grafts revealed a 40% atrophy of the fibers, satellite cell mitotic activity, and reinnervation with great individual variation. Earlier studies of nerve grafts fail to explain the differences in functional outcome by the number and size of regenerated axons. Therefore, an immunohistochemical approach was undertaken to delineate neurotrophic factors active in the free end of human nerve grafts.

Thirty-nine consecutive patients who had received a cross-facial nerve graft had a biopsy taken 4.2–19.6 months later (mean 7.3) from the distal end of the graft at the microneurovascular muscle transfer. Immunohistochemistry and morphometry (semiquantitative grading from 0–3 by two independent observers) for antibodies to NGF receptor (p75) were used to assess neurotrophic activity. Unaltered sural nerve biopsies served as controls. Clinical data, previous histology, functional outcome, and immunohistochemistry were statistically evaluated.

On a scale from 0-3 in graft biopsies taken from the distal end, the expression of NGF-receptor p75 was graded as 3 in 19 cases, as 2 in 15 cases, as 1 in 4 cases, and as 0 in only one nerve graft. In normal sural nerve biopies serving as control samples, there was virtually no expression of NGF-receptor p-75. High p75-expression in graft biopsies correlated with a better functional outcome (p = 0.02).

In this study, the expression of neural growth factor receptor p75 seems to predict the viability of human cross-facial nerve grafts. The possible neurotrophic activity of other growth factors, e.g., VEGF, in this setting remains to be elucidated.