Brian P. Jacob, David C. Chen, Bruce Ramshaw, Shirin Towfigh (eds.) - The SAGES Manual of Groin Pain-Springer International Publishing (2016)

21. Dermatome Mapping: Preoperative and Postoperative Assessment
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Subsequent analysis has allowed us to implement technical modifications
such as extending our evaluation to include the upper third of the thigh,
because we found a high frequency of injury or involvement of the
femoral branch, especially in patients approached laparoscopically. The
dermatome mapping aims to determine the specific source of pain with
regard to type and intensity in order to establish therapeutic guidelines.
Unlike the rest of the proposed assessments that primarily determine the
impact on quality of life in the patient [ 5 , 6 ], we consider the two completely
different evaluation techniques yet highly complementary to
each other.
The current diagnostic methods for the evaluation of chronic postoperative
pain are primarily clinical. Electromyographical studies and
evoked potentials do not show a reliable sensitivity or specificity and are
difficult to implement and interpret. Imaging in general such as computerized
tomography (CT) magnetic resonance imaging (MRI) or ultrasound
(US) has demonstrated only limited utility in cases of granulomas or
meshomas; however, they are of no use in chronic pain of neuropathic
origin.
Technique Description
As a stimulator, a regular ballpoint pen is used to apply the pressure
needed to assess the deep sensation of the dermatome evaluated. Three
permanent markers black, red, and blue (Fig. 21.1 ) are used to mark and
delineate assessed areas.
In all patients with chronic postoperative pain, dermatome mapping
test (DMT) can be implemented using as reference a point one-inch lateral
to the umbilicus contralateral to the region to be evaluated. With respect
to this point, sequentially go from the superior iliac crest to the midline at
a distance of no more than one inch between each point radially, continuing
down to the upper third of the scrotum and penis for males, or the labia
for women. Continue inferiorly to reach and evaluate the upper third of
the thigh, including the anterior, lateral, and medial sides (Figs. 21.2 , 21.3 ,
21.4 , 21.5 , 21.6 , 21.7 , 21.8 , 21.9 , 21.10 , and 21.11 ).
Once the dermatome mapping is completed, proceed to photograph
the area and integrate this into the clinical record in order to have an
objective view of this event. We can follow up with subsequent mapping
to compare with previous DMTs in cases of vague pain scenarios or in
preoperative versus postneurectomy pain assessments after quadruple,
triple, or selective neurectomy.