Corneal and Epidermal Nerve Quantification in Chemotherapy Induced Peripheral Neuropathy

Abstract

Chemotherapy-induced neurotoxicity is an increasingly recognized clinical issue in oncology. in vivo confocal microscopy (IVCM) of corneal nerves has been successfully used to diagnose peripheral neuropathies, including diabetic neuropathy. The purpose of this study was to test if the combination of corneal nerve density and morphology assessed by IVCM is useful to monitor the neurotoxic effects of chemotherapy compared to epidermal nerve quantification. Overall, 95 adult patients with different cancer types were recruited from the oncology and hematology departments of the San Raffaele Hospital. Neurological examination, including clinical Total Neuropathy Score, and in vivo corneal confocal microscopy (IVCM), were performed before and after chemotherapy. In a group of 14 patients, skin biopsy was performed at the first and last visit. In the group of 14 patients who underwent both skin biopsy and corneal nerve imaging, clinical worsening (+69%, p = 0.0018) was paralleled by corneal nerve fiber (CNF) density reduction (-22%, p = 0.0457). Clinical Total neuropathy score significantly worsened from the first to the last visit (+62%, p < 0.0001). CNF length was not significantly reduced overall. However, CNF density/tortuosity ratio significantly decreased after therapy. Correlation analysis showed that the CNF density/tortuosity ratio was also correlated with the number of chemotherapy cycles (r = -0.04790, P = 0.0009). Our data confirm that in vivo corneal confocal microscopy is a helpful, non-invasive tool which shows promise for the diagnosis of chemotherapy-induced peripheral neuropathies. IVCM could allow a rapid, reproducible and non-invasive quantification of peripheral nerve pathology in chemotherapy-associated neuropathy.

Keywords: chemotherapy-induced neuropathy; cornea; corneal confocal microscopy; nerves; neurotoxicity; skin biopsy.

Figure 1

Chemotherapy-induced neuropathy is demonstrated by reduced CNF length/tortuosity index in a large cohort of patients. (A) Clinical TNS calculated in patients before and after therapy. (B) Average ΔTNS calculated before and after the different therapies. Paclitaxel n = 15 patients, Platinum compounds n = 8 patients, VTD n = 9 patients, Cyclophosphamide-combined n = 6 patients. (C) Corneal Nerve Fiber length before and after therapy. (D) Corneal nerve tortuosity obtained by using the short-range tortuosity algorithm before and after the therapy. (E) Corneal Nerve Fiber length—tortuosity ratio before and after therapy. (F) Scatter plot correlating the cumulative dose received from patients treated with paclitaxel with the corneal nerve fiber density/tortuosity ratio. (G) Scatter plot correlating the number of chemotherapy cycles with the corneal nerve fiber density/tortuosity ratio. (H) Scatter plot correlating the number of chemotherapy cycles of paclitaxel with the corneal nerve fiber density/tortuosity ratio. Histograms represent mean values ± SEM; Statistical analysis by Mann-Whitney non-parametric test, One-sample t-test or Spearman's Rank-Order Correlation (*p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001).

Figure 2

Analysis of corneal nerve parameters per drug group in a large cohort of patients. (A) Average ΔCNF length calculated before and after the different therapies. Paclitaxel n = 36 patients, Platinum compounds n = 12 patients, VTD n = 11 patients, Cyclophosphamide-combined n = 15 patients. (B) Average ΔTortuosity calculated before and after the different therapies. Paclitaxel n = 36 patients, Platinum compounds n = 12 patients, VTD n = 11 patients, Cyclophosphamide-combined n = 15 patients. (C) Average ΔCNF length—Tortuosity ratio calculated before and after the different therapies. Paclitaxel n = 36 patients, Platinum compounds n = 12 patients, VTD n = 11 patients, Cyclophosphamide-combined n = 15 patients. Statistical analysis by One sample t-test (**p < 0.01).

Figure 3

Chemotherapy-induced clinical worsening is paralleled by altered corneal but not epidermal nerve morphology in a subset of 14 patients. (A) Clinical TNS calculated in patients before and after the therapy. (B) Epidermal nerve fiber density from skin biopsies obtained in patients before and after the therapy. (C) Corneal Nerve Fiber length before and after therapy. (D) Corneal nerve tortuosity obtained by using the short-range tortuosity algorithm before and after therapy. (E) Corneal Nerve Fiber length—tortuosity ratio before and after therapy. (F) A representative picture of nerve fiber staining with PGP 9.5 (G) representative pictures of in vivo corneal confocal microscopy before and after therapy, which shows a significant reduction of corneal nerve fiber density. Histograms represent mean values ± SEM; Statistical analysis by Mann-Whitney non-parametric test (*p < 0.05, **p < 0.01).