Page 75 - JCBP-2-3

Journal of Clinical and
Basic Psychosomatics HD-tDCS on pain in SSD-P

symptom disorder (SSD), as per the Diagnostic and The current study aimed to investigate the feasibility of
Statistical Manual of Mental Disorders, Fifth Edition this protocol on pain and other associated variables such
(DSM-5), consists of somatic symptoms that are as burden, interference, and disability in SSD-P when
distressing or result in significant disruption in daily life, compared to sham stimulation.
persisting beyond 6 months. Somatic symptom disorder
2
with predominant pain (SSD-P), a specifier for SSD, has 2. Methods
replaced the previous DSM-4 diagnosis of pain disorder, 2.1. Study design and setting
removing the requirement that symptoms should be
medically unexplained. Although the exact prevalence In this study, we employed a single-blind, sham-controlled,
2,3
of SSD-P is not precisely known, it is estimated to affect crossover design, which is advantageous compared to the
about 4% of the population and is associated with a parallel-group design because patients act as their own
significant burden. Treatment options for SSD-P are controls. This study design allows for a lower number
4,5
limited and unsatisfactory with regard to effectiveness of participants and greater homogeneity among study
and convenience. SSD-P is considered difficult to treat subjects. The treatment periods were separated by a
6
due to the challenges associated with existing treatment washout period of 7 days. The study subjects were recruited
modalities. 5 from November 2020 to May 2021 from the outpatient
clinic of the Department of Psychiatry and Neurology
Transcranial direct current stimulation (tDCS) at a tertiary care hospital in North India. Approval was
has been utilized to treat various neurological and obtained from the Institute Ethics Committees where
psychological conditions, including chronic pain. tDCS this study was conducted (INT/IEC/2020/SPL-481). The
7,8
has shown effectiveness in managing chronic pain across study was registered in the Clinical Trials Registry of India
different diagnostic categories, with anodal stimulation (CTRI/2020/10/028752). Figure 1 presents the flowchart of
of the dominant motor cortex or prefrontal cortex the study design.
being common targets. This effectiveness supports the
7
proposed pathophysiology of pain, which suggests that 2.2. Inclusion criteria
pain perception and its emotional impact are influenced Right-handed patients of either gender, diagnosed with
not only by tissue damage but also by central cortical SSD-P as per DSM-5, aged 18 – 60 years, who provided
9
processing. The choice of cortical targets for tDCS is guided written informed consent and were already receiving
by their accessibility, ease of localization, and the proposed any form of stable treatment (defined as no change in
mechanisms of their involvement in painful conditions. treatment over the preceding 3 months), were approached
9
Therefore, it is likely that tDCS could be beneficial in most for inclusion in the study. Patients who consented were
chronic painful conditions, including SSD-P. included after obtaining written informed consent. The
There is a lack of consensus in existing protocols, with HD-tDCS sessions were an add-on to existing treatment,
most studies utilizing conventional tDCS with variable and and no other changes were made to the treatment being
7,10
multiple sessions. The effect of a single tDCS administration received for the duration of the study.
on chronic pain conditions has been assessed in a few studies
and shown to provide significant pain relief. 11-14 2.3. Exclusion criteria
High-definition tDCS (HD-tDCS) is considered an Patients who did not consent to participate in the study,
improvement over conventional tDCS due to its more those diagnosed with Parkinson’s disease, organic brain
focused application of current and precise targeting of syndrome, intellectual disability or dementia, head
underlying brain regions. However, only a limited number injury, uncontrolled epilepsy, encephalopathy due to any
of studies have examined the effect of HD-tDCS on chronic cause, substance dependence disorder other than tobacco
pain, 15,16 and none have studied its impact on SSD-P. In dependence, presence of other cross-sectional or lifetime
this study, we followed a novel protocol involving a single comorbid psychiatric disorders (except for a cross-
session of two administrations of HD-tDCS delivered sectional diagnosis of an anxiety or depressive disorder),
within a 30-min interval. This protocol is a modification of and pregnant females were excluded from the study.
single-session protocols, where it has been observed that In view of the crossover design and as per the available
delivering two sessions within a short interval (within- data on the analgesic benefit of tDCS, it was calculated
18
session repeated tDCS) results in longer-lasting effects that a total of 36 participants (18 per group randomized to
17
due to increased excitability-induced plasticity. Thus, the active tDCS or the sham tDCS conditions) would be
this proposed protocol may represent a viable treatment needed to detect an effect (alpha = 0.05, effect size f = 0.25,
modality. correlation among repeated measures = 0.5) with adequate

Volume 2 Issue 3 (2024) 2 doi: 10.36922/jcbp.2002