Biopsy of the posterior interosseous nerve indicates neuropathy in surgically treated patients with ulnar nerve entrapment - preliminary observations
Erika Nyman, MD PhD1, Seyedamin Razavizadeh, MSc1, Antonia Papadopoulou, MD2, Simin Mohseni, PhD1, Niels Thomsen, MD PhD3 and Lars B. Dahlin, MD, PhD4, (1)Department of Biomedical and Clinical Sciences, Linköping, Sweden, (2)Department of Surgical Sciences, Plastic and Reconstructive surgery, Department of Hand Surgery, Plastic Surgery and Burns, Linköping, Sweden, (3)Department of Hand Surgery, Malmö, Sweden, (4)Hand Surgery, Department of Translational Medicine, Malmö, Sweden
Ulnar nerve entrapment (UNE) produces a variety of symptoms in affected patients. Outcome of surgical treatment may be unpredictable. However, the pathophysiology of UNE is still not clarified. One hypothesis, as in carpal tunnel syndrome (CTS), is that an underlaying peripheral neuropathy makes the ulnar nerve susceptible for entrapment; thereby contributing to an unpredictable outcome of surgery. Our aim was to evaluate any signs of neuropathy in the posterior interosseous nerve (PIN), i.e., a non-compressed nerve, in patients surgically treated for UNE.
In a subproject of a prospective study, evaluating outcome of surgical treatment of UNE, biopsies of PIN were harvested in connection with nerve decompression of the ulnar nerve (n=9; 3 men and 6 women; median [IQR] age 55 [49-64]; concomitant CTS 4/9 patients; smoking 2/7; diabetes 1/9) and compared with postmortem biopsies of PIN from donated cadavers (n=5; 2 men and 3 women; p=0.58; age 78 [73-85]; Mann-Whitney U test p=0.012; no signs of UNE or CTS). The specimens were fixed in 2% glutaraldehyde and 1% formaldehyde in 0.1M phosphate buffer and then processed and sectioned for electron microscopy. Myelinated nerve fiber density (MNFD; no/mm2), diameters of axons and nerve fibers, and g-ratio (diameter axon/diameter nerve fiber) were evaluated together with qualitative grading (demyelination, axonal degeneration and nerve regeneration). In another analysis, nerve biopsies from surgically treated patients with UNE (n=10) were compared with patients with surgery for CTS (n=8).
Findings showed a significantly higher g-ratio among UNE patients (0.63 [0.61-0.66]) compared to control subjects (0.58 [0.55-0.61]; Mann Whitney U test, p=0.012), indicating thinner myelin sheaths of the myelinated nerve fibers, despite control subjects being older. MNFD as well as diameter of axons and nerve fibers did not differ (p=1.00; 0.61 and 0.70, respectively). Both groups displayed signs of pathology based on qualitative judgment (no difference between groups; Chi-squared test p=0.89). Preliminary analyses of PIN from UNE (n=10) and CTS (n=8) show a higher number of small diameter myelinated nerve fibers in UNE, indicating both nerve degeneration and regeneration in biopsies from UNE patients.
Our preliminary data indicate pathological signs of neuropathy in PIN biopsies from surgically treated patients with UNE, indicating an underlaying neuropathy, which may explain suboptimal outcome. Morphometry may reveal subtle morphological changes in nerve biopsies.
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