Dear Editor,
Chronic pain syndromes pose a challenge for interdisciplinary teams of pain specialists.
We report a patient who presented with a neuropathic trigeminal pain syndrome after
repeated resection of an epidermoid tumour involving the trigeminal ganglion. Multiple
therapeutic approaches—including chronic motor cortex stimulation, intrathecal drug
application and deep brain stimulation (DBS) to the periventricular/periaqueductal
grey and sensory thalamus—did not lead to a sustained relief of pain with a persistent
rating of 7-9 on the visual analogue scale (VAS). A magnetic resonance imaging (MRI)
scan was suspicious for a malposition of the previously implanted clinically non-functional
DBS electrodes. The DBS system was completely removed surgically. The patient underwent
diffusion tensor magnetic resonance imaging (DTI). Imaging was performed on a clinical
3-T MRI system (Magnetom Trio Tim System 3 T; Siemens, Erlangen, Germany). DTI: single-shot,
two-dimensional, SE EPI; TR, 10,000 ms; TE, 94 ms; diffusion values, b = 0 s/mm2 and
b = 1,000 s/mm2; diffusion directions, 61; slice count, 69; voxel size, 2.0 × 2.0 × 2.0 mm3;
acquisition time, 11:40 min. Deformation correction of the EPI sequence according
to Zaitsev et al. [1]. DTI tractography: StealthViz-DTI system (Medtronic Navigation,
Louisville, USA); FA level, 0.2; minimal fibre length, 10 mm; seed density, 5.0; maximal
fibre cut-off angle, 50°. Tractography as shown here used the MCP coordinates of the
previous (removed) and newly implanted electrodes. Three-dimensional visualisation
and rendering of tracked fibres were performed with Amira (Konrad Zuse Zemtrum, Berlin,
Germany and Visualization Sciences Group, SAS Bordeaux, France); electric stimulation
as previously described [2].
At the day after imaging, two DBS electrodes were implanted stereotactically, assisted
with the DTI technology (MCP coordinates cross-checked with DTI fibre-tracking results:
VCP: laterality 11 mm, 2-mm anterior to PC, verticality at level of ACPC plane; PVG/PAG:
5-mm laterality, 2-mm anterior PC, verticality at level of ACPC plane).
DTI tractography analysis revealed that the previously misplaced DBS electrodes were
touching the median polysynaptic pain system (MPNS) (Fig. 1a-c, blue arrows). The
newly placed electrodes (as displayed with helical computed tomography) now in addition
reached the medial and trigeminal lemniscal systems (Fig. 1d, e). The patient’s VAS
dropped almost instantaneously and remained stable with fluctuating levels between
2 and 5 over a period of 15 months.
Fig. 1
a–c Deep brain stimulation (DBS) electrode positions (postoperative computed tomography
superimposed onto preoperative T2-weighted MRI scans): a axial view at the level of
the inter-commissural plane; b coronal view; c parasagittal view. Blue arrowheads
in a and c indicate previous implantation site of a DBS electrode (removed). A second
electrode (from a previous operation, removed) was located intraventricularly, its
tract site is not discernible. d, e Results from diffusion tensor imaging (DTI) fibre-tracking
analysis combined with individual electric field simulation studies: d unsuccessful
previous treatment with two DBS electrodes; e successful stimulation attempt over
VCP and PAG DBS electrodes now reaching the medial (blue MPNS) and lateral (pink ML)
systems (acg anterior cingulate gyrus [BA24], ATR anterior thalamic radiation, IC/STP
internal capsule/superior thalamic peduncle, MPNS midline polysynaptic nociceptive
system, VCP nucleus ventralis caudalis posterior, PVG/PAG periventricular grey/periaqueductal
grey, prcg precentral gyrus, pcg postcentral gyrus, sfg superior frontal gyrus, TL/ML
trigeminal lemniscus/medial lemniscus)
Recently, DBS of the medial lemniscus in neuropathic pain after planning with tractography
has been described [3]. This line of investigation is likely to be fruitful in the
light of successful stimulation of fibre tracts in other indications [2, 4–6]. The
PAG/MPNS system is concerned with autonomic, emotional and pain function. In the context
of DBS, the connectivity of the PAG has been previously addressed utilising the DTI
technology [7, 8]. In accordance with our own tractography studies [9], we are convinced
that one previously described upstream projection [8] is confluent with the ATR system
that at different levels (midbrain, PAG, prefrontal cortex, bed-nucleus of the stria
terminalis) connects with the MFB system. Recently we have shown in a pilot study
that direct stimulation of the MFB has strong anti-depressive effects [6]. Since PAG/PVG
stimulation is located in a supposed connection hub of MFB/ATR, it is possible that
PAG stimulation alters the network balance of the ATR system in favour of the MFB
system and diminishes emotional and somatic pain. We have elaborated on the limitations
of the DTI technology in our previous publications [2, 4, 5].
This report strengthens the idea of the application of the DTI tractography technology
for DBS surgery in neuropathic and nociceptive pain and, moreover, for the thorough
analysis of the electrode positions obtained with respect to the fibre systems, which
in addition to computation of somatic pain are concerned with emotion processing.