Lipomatosis of nerve and overgrowth: is there a preference for motor (mixed) vs. sensory nerve involvement?

Background: Lipomatosis of nerve (LN) is a peripheral nerve disorder characterized by fibroadipose proliferation within the epineurium. It has been associated with nerve-territory overgrowth affecting soft tissue and/or bony structures. We sought to understand if there is an anatomical relationship associated with nerve-territory overgrowth. Methods: A review of the literature and our institutional LN cases was performed to determine the prevalence of nerve-territory overgrowth. Only cases with sufficient clinical and/or imaging data were selected. The cases were then subdivided into two groups and analyzed: (1) motor (mixed) nerve and (2) predominant sensory nerve, based on the anatomical location of the LN lesion. Subgroup analysis was performed on median nerves affected by LN, for a more homogenous population. Results: We identified 329 LN cases with sufficient information for analysis. Motor (mixed) nerve group (M) consisted of 287 cases (155 with overgrowth and 132 without overgrowth). Sensory nerve group (S) revealed group of 42 cases (4 cases with overgrowth and 38 without overgrowth). Statistical analysis comparing overgrowth status in the M and S nerve groups showed a statistically significant difference in overgrowth, favoring the M group for overgrowth (p < 0.0001). The analysis of median nerve group consisted of 225 cases in the M group (106 with overgrowth and 119 without overgrowth) and 20 cases in the S group (3 with overgrowth and 17 cases without overgrowth). A statistically significant difference in nerve-territory overgrowth status was present in the M vs. the S group, again favoring the M group for overgrowth. (p = 0.0083). Cases from our institution included 44 cases for this analysis. Forty-two cases in the M group (28 with overgrowth and 14 without overgrowth) and 2 cases in the S group (all 2 without overgrowth). Conclusion: We believe the association of LN and nerve-territory overgrowth might be explained by involvement of mixed motor nerves; however, the exact underlying mechanism is not known.