Clinical, electrophysiological, and cutaneous innervation changes in patients with bortezomib-induced peripheral neuropathy reveal insight into mechanisms of neuropathic pain

Abstract

Bortezomib is a mainstay of therapy for multiple myeloma, frequently complicated by painful neuropathy. The objective of this study was to describe clinical, electrophysiological, and pathological changes of bortezomib-induced peripheral neuropathy (BiPN) in detail and to correlate pathological changes with pain descriptors. Clinical data, nerve conduction studies, and lower leg skin biopsies were collected from 22 BiPN patients. Skin sections were immunostained using anti-protein gene product 9.5 (PGP9.5) and calcitonin gene-related peptide (CGRP) antibodies. Cumulative bortezomib dose and clinical assessment scales indicated light-moderate sensory neuropathy. Pain intensity >4 (numerical rating scale) was present in 77% of the patients. Median pain intensity and overall McGill Pain Questionnaire (MPQ) sum scores indicated moderate to severe neuropathic pain. Sural nerve sensory nerve action potentials were abnormal in 86%, while intraepidermal nerve fiber densities of PGP9.5 and CGRP were not significantly different from healthy controls. However, subepidermal nerve fiber density (SENFD) of PGP9.5 was significantly decreased and the axonal swelling ratio, a predictor of neuropathy, and upper dermis nerve fiber density (UDNFD) of PGP9.5, presumably representing sprouting of parasympathetic fibers, were significantly increased in BiPN patients. Finally, significant correlations between UDNFD of PGP9.5 versus the evaluative Pain Rating Index (PRI) and number of words count (NWC) of the MPQ, and significant inverse correlations between SENFD/UDNFD of CGRP versus the sensory-discriminative MPQ PRI/NWC were found. BiPN is a sensory neuropathy, in which neuropathic pain is the most striking clinical finding. Bortezomib-induced neuropathic pain may be driven by sprouting of parasympathetic fibers in the upper dermis and impaired regeneration of CGRP fibers in the subepidermal layer.

Keywords: (non)peptidergic; Bortezomib; McGill Pain Questionnaire; calcitonin gene-related peptide; epidermal innervation; nerve conduction studies; neuropathic pain; neuropathy; parasympathetic; protein gene product 9.5.

Figure 1.

Immunohistochemical staining patterns of PGP9.5 (a and c) and CGRP (b and d) in BiPN patients (a and b) and healthy volunteers (c and d). (e) to (h) represent high-power insets, which enable to visualize the length of the intraepidermal fibers, branching pattern and intraepidermal axonal swellings. Red arrows represent intraepidermal nerve fibers, white arrows represent subepidermal nerve fibers, black arrows represent upper dermal nerve fibers, and green arrows represent axonal swellings. The white bars measure 50 µm. CGRP: calcitonin gene-related peptide; PGP9.5: protein gene product 9.5.

Figure 2.

Immunohistochemical staining patterns of PGP9.5 (a) and CGRP (guinea-pig) (c) and using preabsorbtion controls (b and d), in normal skins. Immunohistochemical staining patterns in normal skins, comparing a guinea pig (e) and a rabbit anti-CCRP antibody (f). The white bar measures 50 µm.

Figure 3.

Skin innervation measurements in BiPN patients (n = 22) and healthy volunteers (n = 17). Box plots showing the median, interquartile range, range, and outliers of the number of intraepidermal (IENFD; a), subepidermal (SENFD; c), upper dermal (UDNFD; d) nerve fiber density, and the axonal swelling ratios (b), using PGP9.5, CGRP, and (PGP9.5-CGRP) as markers to measure the total number of fibers and peptidergic and nonpeptidergic subclasses, ***p ≤ 0.001; Mann–Whitney tests, using Bonferroni correction with an adjusted significance level of 0.017.