9. Subclinical peripheral neuropathy prior to chemotherapy in colorectal cancer patients – Myth or reality?

Abstract

Background Several studies have reported subclinical deficits in sensory nerve function, as evidenced by quantitative sensory testing, in adult patients with colorectal cancer prior to any exposure to neurotoxic chemotherapy. These studies, however, have not correlated the quantitative sensory testing with objective neurophysiological studies. If present, this could be an important risk factor for developing chemotherapy induced peripheral neuropathy. Aim To determine whether patients with colorectal cancer have subclinical peripheral neuropathy, before commencing neurotoxic chemotherapy. Method Assessments were undertaken in 87 participants with colorectal cancer prior to initiation of chemotherapy. Clinical and functional findings were correlated with conventional nerve conduction studies and specialised nerve excitability techniques. Data were compared to normal controls or normative reference ranges. Results Mean lower limb sural sensory amplitude for colorectal patients aged ⩽ 39, 40–59 and ⩾ 60years were 21.4 ± 2.7 μ V, 16.0 ± 1.1 μ V and 13.5 ± 1.5 μ V respectively, with 85 of 86 individual values falling within our laboratory normative reference values for age. All lower limb tibial motor amplitudes and upper limb superficial radial amplitudes were also within normative reference values for age. No significant difference was seen in multiple median sensory nerve excitability parameters between colorectal patients ( n =60) and controls including refractoriness at 2.5ms (colorectal 22.84 ± 2.32%, controls 19.30 ± 2.53%, p =0.56), superexcitability (colorectal −16.54 ± 0.76%, controls −18.53 ± 1.30%, p =0.11) and hyperpolarising threshold electrotonus at 90–100ms (colorectal −129.57 ± 2.5%, controls −123.35 ± 4.13%, p =0.13). Clinical history and examination findings were obtained in a subset of 52 participants. 39/52 (75%) participants had no peripheral sensory or motor symptoms or examination abnormalities. 13/52 had distal symptoms and/or signs in 1–2 modalities (reduced ankle jerks, vibration and pinprick sensibilities in toes) which did not correlate with abnormalities on conventional nerve conduction studies. 11/13 patients were > 60years of age and these isolated changes can also be seen in older individuals in the normal population. Conclusion This study demonstrates that there is a low likelihood of significant distal symmetrical polyneuropathy in colorectal cancer patients, prior to chemotherapy initiation.