Close apposition and exposure of non-myelinated axons in traumatic neuromas of the human lingual nerve.
Peripheral nerve injury is sometimes followed by the development of persistent painful sensory disorders, such as dysaesthesia. The aetiology of these disorders is not clear, but abnormal behaviour of damaged axons at the injury site is likely to be involved. In this study, we quantified some ultrastructural characteristics that may be related to the development of abnormal spontaneous activity, sympathetic interactions, and fibre-to-fibre crosstalk. Using electron microscopy, we have determined the frequency and extent of axonal exposure and close apposition among non-myelinated axons from 34 traumatic neuromas of the human lingual nerve. These specimens were removed at the time of microsurgical nerve repair, and the presence or absence of symptoms of dysaesthesia was determined pre-operatively. Comparisons were also made with eight normal control lingual nerve specimens obtained from patients undergoing organ donor retrieval. More non-myelinated axons showed signs of axonal exposure in traumatic neuromas (26%) than in controls (5%), and exposure was higher in nerve-end neuromas (31%) than in neuromas-in-continuity (22%). In addition, the proportion of the non-myelinated axolemma that was exposed was significantly higher in neuromas (32%) than in controls (21%). The frequency of close apposition between neighbouring non-myelinated axons was also higher in neuromas (11%) than in controls (0.35%). The majority of axons showing signs of exposure or close apposition had diameters <1 microm. These ultrastructural changes may account for some of the altered electrophysiological properties of axons within neuromas. However, no significant correlations were found between these ultrastructural characteristics and the patients' reported symptoms of dysaesthesia.
Vora
Amit R
AR
Department of Oral & Maxillofacial Surgery, School of Clinical Dentistry, University of Sheffield, Sheffield, UK.
Loescher
Alison R
AR
Boissonade
Fiona M
FM
Robinson
Peter P
PP
D000293:Adolescent; D000328:Adult; D002450:Cell Communication / Q000502:physiology*; D006801:Humans; D008036:Lingual Nerve / Q000473:pathology* / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D008875:Middle Aged; D036421:Nerve Fibers, Unmyelinated / Q000648:ultrastructure*; D009463:Neuroma / Q000473:pathology / Q000648:ultrastructure*