Determining the efficacy of chordotomy using laser evoked potentials: a pilot study

Percutaneous cervical chordotomy (PCC) is a neurolytic technique which destroys
nociceptive pathways in the spinal cord [Mullan et al, 1963]. PCC is often used
to control intractable unilateral pain due to cancer and compression of
surrounding neuronal tissues. It is particularly effective in managing severe
chest pain, known as the costopleural syndrome, accompanying malignant
mesothelioma. This method is described to exert significant pain relief in 83%
of patients with pleural mesothelioma [Jackson et al, 1999]. The degree of
effectiveness is mainly based on the extent in which opioïd intake decreases
after the procedure, which seems rather insufficient to objectively determine
spinothalamic tract function. Therefore, a quantifiable method to evaluate the
functional integrity of the nociceptive system after PCC, might be useful.
Laser stimuli can be applied to selectively activate pain receptors in the
skin, and generate an afferent volley in poorly myelinated Aδ and unmyelinated
C fibers that, upon arrival to the central nervous system, can be recorded at
the vertex as laser-evoked-potentials (LEPs) [Schestatsky et al, 2007]. In
healthy subjects it shows a negative-positive complex, comprising a N2 and P2
component, in a time window between 175-500ms after stimulation [Treede et al,
2003]. These waveforms reflect nociceptive responses and correlates with the
functional integrity of the spinothalamic tract. Pathological LEP reductions
occur for certain lesions of the peripheral nerve, plexus, root or spinal cord
[Treede et al, 2003]. Therefore, LEPs can be useful for objectively confirming
impairment of nociceptive pathways. The aim of this study is to assess if LEPs
can reliably be used to determine the efficacy of PCC. Furthermore, the change
in opioid consumption will be evaluated using a pain diary.

Primary Objective: Evaluate the functional integrity of the nociceptive system
after percutaneous cervical chordotomy using Laser Evoked Potentials

Secondary Objective(s): change in opioid consumption after percutaneous
cervical chordotomy using a pain diary

This study is a prospective, observational, mono-center pilot-study. 5 study
subjects will participate in this pilot study at the outpatient Neurophysiology
clinic of the St. Antonius Hospital Nieuwegein. Subjects will be screened upon
the inclusion and exclusion criterion, consented, and enrolled in the study
from November 2014 - November 2015.

Laser stimulation session
Cutaneous heat stimuli are delivered by a 980-nm diode laser (Biolitec, Ceram
Optec, Bonn, Germany) to the blackened dorsum of the right and left hand (C6
dermatome). Blackening of the skin is performed to rule out bias by differences
in skin pigmentation. Laser intensity is set at 1.0-2.5W (10-25 mJ/mm2),
duration of the stimuli is set at 50 msec, with a laser beam spotsize of 5 mm2.
The stimulus intensity will be adjusted to evoke a clear pinprick sensation
(before the PCC is performed). Interstimulus duration randomly varies between 5
and 10 sec to assure reorientation of attention to an unexpected stimulus. 10
laser stimulations will be adminstrated. In the second stimulation session
(after PCC) the same laser settings will be used. Our study group is
experienced in using this non-invasive device [MEC ID: R-06.38A, GOV ID:
NL14786.100.06; Korenromp et al, 2012].

Recording and Processing
Electroencephalography (EEG) recordings will be made to measure brain activity
following laser stimulation. EEG epochs recorded 200 msec before and 800 msec
after the onset of each stimulus.

Risks during participation in this study are negligible. Stimulation of Aδ
nerve fibers testing using 980nm diode laser stimulation might induce a pinprick
feeling in participants and some mild skin redness which will resolve
spontaneously.