Is the Volume of the Caudate Nuclei Associated With Area of Secondary Hyperalgesia? – Protocol for a 3-Tesla MRI Study of Healthy Volunteers

Background Experience and development of pain may be influenced by a number of physiological, psychological, and psychosocial factors. In a previous study we found differences in neuronal activation to noxious stimulation, and microstructural neuroanatomical differences, when comparing healthy volunteers with differences in size of the area of secondary hyperalgesia following a standardized burn injury. Objective We aim to investigate the degree of association between the volume of pain-relevant structures in the brain and the size of the area of secondary hyperalgesia following brief thermal sensitization. Methods The study consists of one experimental day, in which whole-brain magnetic resonance imaging (MRI) scans will be conducted including T1-weighed three-dimensional anatomy scan, diffusion tensor imaging, and resting state functional MRI. Before the experimental day, all included participants will undergo experimental pain testing in a parallel study (Clinicaltrials.gov Identifier: NCT02527395). Results from this experimental pain testing, as well as the size of the area of secondary hyperalgesia from the included participants, will be extracted from this parallel study. Results The association between the volume of pain-relevant structures in the brain and the area of secondary hyperalgesia will be investigated by linear regression of the estimated best linear unbiased predictors on the individual volumes of the pain relevant brain structures. Conclusions We plan to investigate the association between experimental pain testing parameters and the volume, connectivity, and resting state activity of pain-relevant structures in the brain. These results may improve our knowledge of the mechanisms responsible for the development of acute and chronic pain. ClinicalTrial Danish Research Ethics Committee (identifier: H-15010473). Danish Data Protection Agency (identifier: RH-2015-149). Clinicaltrials.gov NCT02567318; http://clinicaltrials.gov/ct2/show/NCT02567318 (Archived by WebCite at http://www.webcitation.org/6i4OtP0Oi)


APPENDIX 2 Other tests and evaluations
The following tests and evaluations are not conducted in this study, but are conducted in the study: "To determine the degree of association between Heat Pain Detection Threshold and area of secondary hyperalgesia following Brief Thermal Sensitization in healthy male volunteers" (Clinical trials identifier: NCT02527395) that have previously been approved by the regional Committee on Health Research Ethics (protocol number: H-8-2014-012). Thus, the following descriptions are for informational purposes only.

Pain assessment
Pain is assessed with a Visual analogue scale (VAS), index from 0-100 mm, where 0 mm represents "no pain", and 100 mm represents "the worst pain imaginable".

Brief thermal sensitization (BTS)
A computer-controlled thermode (Somedic MSA Thermotester TM ; size 2.5x5 cm) is placed on the participant's skin, and the skin is heated to 45°C for 3 min. After 3 min., while the thermode still has contact with the skin, the assessment of secondary hyperalgesia is conducted. The test is conducted on the anterior right thigh.

Assessment of secondary hyperalgesia
The area of secondary hyperalgesia is quantified after stimulation with a 19G monofilament (von Frey hair) in 4 linear paths arranged in 90° around the centre of stimulation. Stimulation will begin 15 cm. from the centre of stimulation and advance in steps of 5 mm. with 1 second intervals towards the centre of stimulation. When the participant states a clear change in sensation the place will be marked with a felt pen and the transverse and longitudinal axes will be measured for later area calculation.

Pain during thermal stimulation (p-TS)
The computer-controlled thermode is placed on the participant's skin, and the skin is heated to 45°C for 1 min. During this the participant evaluates the pain with an electronic VAS-scale. The participant will continuously evaluate the pain using the electronic VAS-scale because of the fluctuations in pain intensity during this type of stimulation. The equipment automatically Is the volume of the caudate nuclei associated with area of secondary hyperalgesia? -Protocol for a 3-tesla MRI study of healthy volunteers calculates a VAS-score under the curve (VAS-AUC) and a maximum VAS-score for the time period. The participant will not be able to see the computer screen during the measurement, and each pain evaluation will be independent of the previous evaluation. The test is conducted centrally on the anterior part of the non-dominant lower arm

Heat pain detection threshold (HPDT)
Heat pain detection threshold represents the lowest temperature that is perceived as painful, when heating the skin with the computer-controlled thermode. The initial temperature is 32°C, and temperature is increased 1°C/sec. The participant is asked to press a button when the heat is perceived as painful. If 52°C (the maximum temperature for the thermode) is reached before the participant's threshold has been registered, the thermode will automatically return to the initial temperature of 32°C. The HPDT is calculated as an average of four stimulations. Each stimulation will be performed with an interval of 6-10 seconds. The test is conducted on the anterior of the dominant lower arm.

Hospital Anxiety and Depression scale (HADS)
HADS is a questionnaire consisting of 14 questions, and is a 4-point Likert scale with values from 0-3. HADS can be subdivided into HADS-A, evaluating anxiety, and HADS-D, evaluating depression. The highest achievable score is 42, and a total HADS-score will estimate the participant's level of distress. To evaluate anxiety and depression separately, HADS-A and HADS-D must be evaluated separately, with a maximum score of 21 in the two subtests.
The interpretation of the score in HADS-A and HADS-D is as follows: -0-7: Normal -8: Mild level of anxiety/depression -11-15: Moderate level of anxiety/depression ->16: Severe level of anxiety/depression The HADS questionnaire is to be completed before study day 1.

Pain Catastrophizing Scale (PCS)
PCS is a questionnaire consisting of 13 questions. PCS is a 5-point Likert scale with values from 0-4, and can be subdivided into 3 subtests, that each evaluates the central elements in catastrophizing: Is the volume of the caudate nuclei associated with area of secondary hyperalgesia? -Protocol for a 3-tesla MRI study of healthy volunteers Rumination, magnification and helplessness. The highest achievable score is 52, and with separate evaluation of the three subtests, the 3 different elements can be assessed individually. To evaluate the 3 elements separately the 13 questions must be evaluated in the 3 following subgroups: -Rumination: The sum of question 8, 9, 10, 11. Maximal sum =16 -Magnification: The sum of question 6, 7, 13. Maximal sum = 12 -Helplessness: The sum of question 1, 2, 3, 4, 5, 12. Maximal sum = 24 The PCS questionnaire is to be completed before study day 1.