| Abstract|| |
Electroconvulsive therapy (ECT) is an effective modality of treatment for a variety of psychiatric disorders. However, it has always been accused of being a coercive, unethical, and dangerous modality of treatment. The dangerousness of ECT has been mainly attributed to its claimed ability to cause brain damage. This narrative review aims to provide an update of the evidence with regard to whether the practice of ECT is associated with damage to the brain. An accepted definition of brain damage remains elusive. There are also ethical and technical problems in designing studies that look at this question specifically. Thus, even though there are newer technological tools and innovations, any review attempting to answer this question would have to take recourse to indirect methods. These include structural, functional, and metabolic neuroimaging; body fluid biochemical marker studies; and follow-up studies of cognitive impairment and incidence of dementia in people who have received ECT among others. The review of literature and present evidence suggests that ECT has a demonstrable impact on the structure and function of the brain. However, there is a lack of evidence at present to suggest that ECT causes brain damage.
Keywords: Adverse effect, brain damage, electroconvulsive therapy
|How to cite this article:|
Jolly AJ, Singh SM. Does electroconvulsive therapy cause brain damage: An update. Indian J Psychiatry 2020;62:339-53
| Introduction|| |
Electroconvulsive therapy (ECT) as a modality of treatment for psychiatric disorders has existed at least since 1938. ECT is an effective modality of treatment for various psychiatric disorders. However, from the very beginning, the practice of ECT has also faced resistance from various groups who claim that it is coercive and harmful. While the ethical aspects of the practice of ECT have been dealt with elsewhere, the question of harmfulness or brain damage consequent upon the passage of electric current needs to be examined afresh in light of technological advances and new knowledge.
The question whether ECT causes brain damage was reviewed in a holistic fashion by Devanand et al. in the mid-1990s., The authors had attempted to answer this question by reviewing the effect of ECT on the brain in various areas – cognitive side effects, structural neuroimaging studies, neuropathologic studies of patients who had received ECT, autopsy studies of epileptic patients, and finally animal ECS studies. The authors had concluded that ECT does not produce brain damage.
This narrative review aims to update the evidence with regard to whether ECT causes brain damage by reviewing relevant literature from 1994 to the present time.
| Framing the Question|| |
The Oxford Dictionary defines damage as physical harm that impairs the value, usefulness, or normal function of something. Among medical dictionaries, the Peter Collins Dictionary defines damage as harm done to things (noun) or to harm something (verb). Brain damage is defined by the British Medical Association Medical Dictionary as degeneration or death of nerve cells and tracts within the brain that may be localized to a particular area of the brain or diffuse. Going by such a definition, brain damage in the context of ECT should refer to death or degeneration of brain tissue, which results in the impairment of functioning of the brain. The importance of precisely defining brain damage shall become evident subsequently in this review.
There are now many more tools available to investigate the structure and function of brain in health and illness. However, there are obvious ethical issues in designing human studies that are designed to answer this specific question. Therefore, one must necessarily take recourse to indirect evidences available through studies that have been designed to answer other research questions. These studies have employed the following methods:
- Structural neuroimaging studies
- Functional neuroimaging studies
- Metabolic neuroimaging studies
- Body fluid biochemical marker studies
- Cognitive impairment studies.
While the early studies tended to focus more on establishing the safety of ECT and finding out whether ECT causes gross microscopic brain damage, the later studies especially since the advent of advanced neuroimaging techniques have been focusing more on a mechanistic understanding of ECT. Hence, the primary objective of the later neuroimaging studies has been to look for structural and functional brain changes which might explain how ECT acts rather than evidence of gross structural damage per se; however, put together, all these studies would enable us to answer our titular question to some satisfaction. [Table 1] and [Table 2] provide an overview of the evidence base in this area.
| Structural and Functional Neuroimaging Studies|| |
Devanand et al. reviewed 16 structural neuroimaging studies on the effect of ECT on the brain. Of these, two were pneumoencephalography studies, nine were computed tomography (CT) scan studies, and five were magnetic resonance imaging (MRI) studies. However, most of these studies were retrospective in design, with neuroimaging being done in patients who had received ECT in the past. In the absence of baseline neuroimaging, it would be very difficult to attribute any structural brain changes to ECT. In addition, pneumoencephalography, CT scan, and even early 0.3 T MRI provided images with much lower spatial resolution than what is available today. The authors concluded that there was no evidence to show that ECT caused any structural damage to the brain. Since then, at least twenty more MRI-based structural neuroimaging studies have studied the effect of ECT on the brain. The earliest MRI studies in the early 1990s focused on detecting structural damage following ECT. All of these studies were prospective in design, with the first MRI scan done at baseline and a second MRI scan performed post ECT.,,,, While most of the studies imaged the patient once around 24 h after receiving ECT, some studies performed multiple post ECT neuroimaging in the first 24 h after ECT to better capture the acute changes. A single study by Coffey et al. followed up the patients for a duration of 6 months and repeated neuroimaging again at 6 months in order to capture any long-term changes following ECT.
The most important conclusion which emerged from this early series of studies was that there was no evidence of cortical atrophy, change in ventricle size, or increase in white matter hyperintensities. The next major conclusion was that there appeared to be an increase in the T1 and T2 relaxation time immediately following ECT, which returned to normal within 24 h. This supported the theory that immediately following ECT, there appears to be a temporary breakdown of the blood–brain barrier, leading to water influx into the brain tissue. The last significant observation by Coffey et al. in 1991 was that there was no significant temporal changes in the total volumes of the frontal lobes, temporal lobes, or amygdala–hippocampal complex. This was, however, something which would later be refuted by high-resolution MRI studies. Nonetheless, one inescapable conclusion of these early studies was that there was no evidence of any gross structural brain changes following administration of ECT. Much later in 2007, Szabo et al. used diffusion-weighted MRI to image patients in the immediate post ECT period and failed to observe any obvious brain tissue changes following ECT.
The next major breakthrough came in 2010 when Nordanskog et al. demonstrated that there was a significant increase in the volume of the hippocampus bilaterally following a course of ECT in a cohort of patients with depressive illness. This contradicted the earlier observations by Coffey et al. that there was no volume increase in any part of the brain following ECT. This was quite an exciting finding and was followed by several similar studies. However, the perspective of these studies was quite different from the early studies. In contrast to the early studies looking for the evidence of ECT-related brain damage, the newer studies were focused more on elucidating the mechanism of action of ECT. Further on in 2014, Nordanskog et al. in a follow-up study showed that though there was a significant increase in the volume of the hippocampus 1 week after a course of ECT, the hippocampal volume returned to the baseline after 6 months. Two other studies in 2013 showed that in addition to the hippocampus, the amygdala also showed significant volume increase following ECT., A series of structural neuroimaging studies after that have expanded on these findings and as of now, gray matter volume increase following ECT has been demonstrated in the hippocampus, amygdala, anterior temporal pole, subgenual cortex, right caudate nucleus, and the whole of the medial temporal lobe (MTL) consisting of the hippocampus, amygdala, insula, and the posterosuperior temporal cortex, para hippocampi, right subgenual anterior cingulate gyrus, and right anterior cingulate gyrus, left cerebellar area VIIa crus I, putamen, caudate nucleus, and nucleus acumbens  and clusters of increased cortical thickness involving the temporal pole, middle and superior temporal cortex, insula, and inferior temporal cortex. However, the most consistently reported and replicated finding has been the bilateral increase in the volume of the hippocampus and amygdala. In light of these findings, it has been tentatively suggested that ECT acts by inducing neuronal regeneration in the hippocampus – amygdala complex., However, there are certain inconsistencies to this hypothesis. Till date, only one study – Nordanskog et al., 2014 – has followed study patients for a long term – 6 months in their case. And significantly, the authors found out that after increasing immediately following ECT, the hippocampal volume returns back to baseline by 6 months. This, however, was not associated with the relapse of depressive symptoms. Another area of significant confusion has been the correlation of hippocampal volume increase with improvement of depressive symptoms. Though almost all studies demonstrate a significant increase in hippocampal volume following ECT, a majority of studies failed to demonstrate a correlation between symptom improvement and hippocampal volume increase.,,,, However, a significant minority of volumetric studies have demonstrated correlation between increase in hippocampal and/or amygdala volume and improvement of symptoms.,,
Another set of studies have used diffusion tensor imaging, functional MRI (fMRI), anatomical connectome, and structural network analysis to study the effect of ECT on the brain. The first of these studies by Abbott et al. in 2014 demonstrated that on fMRI, the connectivity between right and left hippocampus was significantly reduced in patients with severe depression. It was also shown that the connectivity was normalized following ECT, and symptom improvement was correlated with an increase in connectivity. In a first of its kind DTI study, Lyden et al. in 2014 demonstrated that fractional anisotropy which is a measure of white matter tract or fiber density is increased post ECT in patients with severe depression in the anterior cingulum, forceps minor, and the dorsal aspect of the left superior longitudinal fasciculus. The authors suggested that ECT acts to normalize major depressive disorder-related abnormalities in the structural connectivity of the dorsal fronto-limbic pathways. Another DTI study in 2015 constructed large-scale anatomical networks of the human brain – connectomes, based on white matter fiber tractography. The authors found significant reorganization in the anatomical connections involving the limbic structure, temporal lobe, and frontal lobe. It was also found that connection changes between amygdala and para hippocampus correlated with reduction in depressive symptoms. In 2016, Wolf et al. used a source-based morphometry approach to study the structural networks in patients with depression and schizophrenia and the effect of ECT on the same. It was found that the medial prefrontal cortex/anterior cingulate cortex (ACC/MPFC) network, MTL network, bilateral thalamus, and left cerebellar regions/precuneus exhibited significant difference between healthy controls and the patient population. It was also demonstrated that administration of ECT leads to significant increase in the network strength of the ACC/MPFC network and the MTL network though the increase in network strength and symptom amelioration were not correlated.
Building on these studies, a recently published meta-analysis has attempted a quantitative synthesis of brain volume changes – focusing on hippocampal volume increase following ECT in patients with major depressive disorder and bipolar disorder. The authors initially selected 32 original articles from which six articles met the criteria for quantitative synthesis. The results showed significant increase in the volume of the right and left hippocampus following ECT. For the rest of the brain regions, the heterogeneity in protocols and imaging techniques did not permit a quantitative analysis, and the authors have resorted to a narrative review similar to the present one with similar conclusions. Focusing exclusively on hippocampal volume change in ECT, Oltedal et al. in 2018 conducted a mega-analysis of 281 patients with major depressive disorder treated with ECT enrolled at ten different global sites of the Global ECT-MRI Research Collaboration. Similar to previous studies, there was a significant increase in hippocampal volume bilaterally with a dose–response relationship with the number of ECTs administered. Furthermore, bilateral (B/L) ECT was associated with an equal increase in volume in both right and left hippocampus, whereas right unilateral ECT was associated with greater volume increase in the right hippocampus. Finally, contrary to expectation, clinical improvement was found to be negatively correlated with hippocampal volume.
Thus, a review of the current evidence amply demonstrates that from looking for ECT-related brain damage – and finding none, we have now moved ahead to looking for a mechanistic understanding of the effect of ECT. In this regard, it has been found that ECT does induce structural changes in the brain – a fact which has been seized upon by some to claim that ECT causes brain damage. Such statements should, however, be weighed against the definition of damage as understood by the scientific medical community and patient population. Neuroanatomical changes associated with effective ECT can be better described as ECT-induced brain neuroplasticity or ECT-induced brain neuromodulation rather than ECT-induced brain damage.
| Metabolic Neuroimaging Studies: Magnetic Resonance Spectroscopic Imaging|| |
Magnetic resonance spectroscopic imaging (MRSI) uses a phase-encoding procedure to map the spatial distribution of magnetic resonance (MR) signals of different molecules. The crucial difference, however, is that while MRI maps the MR signals of water molecules, MRSI maps the MR signals generated by different metabolites – such as N-acetyl aspartate (NAA) and choline-containing compounds. However, the concentration of these metabolites is at least 10,000 times lower than water molecules and hence the signal strength generated would also be correspondingly lower. However, MRSI offers us the unique advantage of studying in vivo the change in the concentration of brain metabolites, which has been of great significance in fields such as psychiatry, neurology, and basic neuroscience research.
MRSI studies on ECT in patients with depression have focused largely on four metabolites in the human brain – NAA, choline-containing compounds (Cho) which include majorly cell membrane compounds such as glycerophosphocholine, phosphocholine and a miniscule contribution from acetylcholine, creatinine (Cr) and glutamine and glutamate together (Glx). NAA is located exclusively in the neurons, and is suggested to be a marker of neuronal viability and functionality. Choline-containing compounds (Cho) mainly include the membrane compounds, and an increase in Cho would be suggestive of increased membrane turnover. Cr serves as a marker of cellular energy metabolism, and its levels are usually expected to remain stable. The regions which have been most widely studied in MRSI studies include the bilateral hippocampus and amygdala, dorsolateral prefrontal cortex (DLPFC), and ACC.
Till date, five MRSI studies have measured NAA concentration in the hippocampus before and after ECT. Of these, three studies showed that there is no significant change in the NAA concentration in the hippocampus following ECT.,, On the other hand, two recent studies have demonstrated a statistically significant reduction in NAA concentration in the hippocampus following ECT., The implications of these results are of significant interest to us in answering our titular question. A normal level of NAA following ECT could signify that there is no significant neuronal death or damage following ECT, while a reduction would signal the opposite. However, a direct comparison between these studies is complicated chiefly due to the different ECT protocols, which has been used in these studies. It must, however, be acknowledged that the three older studies used 1.5 T MRI, whereas the two newer studies used a higher 3 T MRI which offers betters signal-to-noise ratio and hence lesser risk of errors in the measurement of metabolite concentrations. The authors of a study by Njau et al. argue that a change in NAA levels might reflect reversible changes in neural metabolism rather than a permanent change in the number or density of neurons and also that reduced NAA might point to a change in the ratio of mature to immature neurons, which, in fact, might reflect enhanced adult neurogenesis. Thus, the authors warn that to conclude whether a reduction in NAA concentration is beneficial or harmful would take a simultaneous measurement of cognitive functioning, which was lacking in their study. In 2017, Cano et al. also demonstrated a significant reduction in NAA/Cr ratio in the hippocampus post ECT. More significantly, the authors also showed a significant increase in Glx levels in the hippocampus following ECT, which was also associated with an increase in hippocampal volume. To explain these three findings, the authors proposed that ECT produces a neuroinflammatory response in the hippocampus – likely mediated by Glx, which has been known to cause inflammation at higher concentrations, thereby accounting for the increase in hippocampal volume with a reduction in NAA concentration. The cause for the volume increase remains unclear – with the authors speculating that it might be due to neuronal swelling or due to angiogenesis. However, the same study and multiple other past studies ,, have demonstrated that hippocampal volume increase was correlated with clinical improvement following ECT. Thus, we are led to the hypothesis that the same mechanism which drives clinical improvement with ECT is also responsible for the cognitive impairment following ECT. Whether this is a purely neuroinflammatory response or a neuroplastic response or a neuroinflammatory response leading to some form of neuroplasticity is a critical question, which remains to be answered.
Studies which have analyzed NAA concentration change in other brain areas have also produced conflicting results. The ACC is another area which has been studied in some detail utilizing the MRSI technique. In 2003, Pfleiderer et al. demonstrated that there was no significant change in the NAA and Cho levels in the ACC following ECT. This would seem to suggest that there was no neurogenesis or membrane turnover in the ACC post ECT. However, this finding was contested by Merkl et al. in 2011, who demonstrated that NAA levels were significantly reduced in the left ACC in patients with depression and that these levels were significantly elevated following ECT. This again is contested by Njau et al. who showed that NAA levels are significantly reduced following ECT in the left dorsal ACC. A direct comparison of these three studies is complicated by the different ECT and imaging parameters used and hence, no firm conclusion can be made on this point at this stage. In addition to this, one study had demonstrated increased NAA levels in the amygdala following administration of ECT, with a trend level increase in Cho levels, which again is suggestive of neurogenesis and/or neuroplasticity. A review of studies on the DLPFC reveals a similarly confusing picture with one study, each showing no change, reduction, and elevation of concentration of NAA following ECT.,, Here, again, a direct comparison of the three studies is made difficult by the heterogeneous imaging and ECT protocols followed by them.
A total of five studies have analyzed the concentration of choline-containing compounds (Cho) in patients undergoing ECT. Conceptually, an increase in Cho signals is indicative of increased membrane turnover, which is postulated to be associated with synaptogenesis, neurogenesis, and maturation of neurons. Of these, two studies measured Cho concentration in the B/L hippocampus, with contrasting results. Ende et al. in 2000 demonstrated a significant elevation in Cho levels in B/L hippocampus after ECT, while Jorgensen et al. in 2015 failed to replicate the same finding., Cho levels have also been studied in the amygdala, ACC, and the DLPFC. However, none of these studies showed a significant increase or decrease in Cho levels before and after ECT in the respective brain regions studied. In addition, no significant difference was seen in the pre-ECT Cho levels of patients compared to healthy controls.,,
In review, we must admit that MRSI studies are still at a preliminary stage with significant heterogeneity in ECT protocols, patient population, and regions of the brain studied. At this stage, it is difficult to draw any firm conclusions except to acknowledge the fact that the more recent studies – Njau et al., 2017, Cano, 2017, and Jorgensen et al., 2015 – have shown decrease in NAA concentration and no increase in Cho levels ,, – as opposed to the earlier studies by Ende et al. The view offered by the more recent studies is one of a neuroinflammatory models of action of ECT, probably driving neuroplasticity in the hippocampus. This would offer a mechanistic understanding of both clinical response and the phenomenon of cognitive impairment associated with ECT. However, this conclusion is based on conjecture, and more work needs to be done in this area.
| Body Fluid Biochemical Marker Studies|| |
Another line of evidence for analyzing the effect of ECT on the human brain is the study of concentration of neurotrophins in the plasma or serum. Neurotrophins are small protein molecules which mediate neuronal survival and development. The most prominent among these is brain-derived neurotrophic factor (BDNF) which plays an important role in neuronal survival, plasticity, and migration. A neurotrophic theory of mood disorders was suggested which hypothesized that depressive disorders are associated with a decreased expression of BDNF in the limbic structures, resulting in the atrophy of these structures. It was also postulated that antidepressant treatment has a neurotrophic effect which reverses the neuronal cell loss, thereby producing a therapeutic effect. It has been well established that BDNF is decreased in mood disorders. It has also been shown that clinical improvement of depression is associated with increase in BDNF levels. Thus, serum BDNF levels have been tentatively proposed as a biomarker for treatment response in depression. Recent meta-analytic evidence has shown that ECT is associated with significant increase in serum BDNF levels in patients with major depressive disorder. Considering that BDNF is a potent stimulator of neurogenesis, the elevation of serum BDNF levels following ECT lends further credence to the theory that ECT leads to neurogenesis in the hippocampus and other limbic structures, which, in turn, mediates the therapeutic action of ECT.
| Cognitive Impairment Studies|| |
Cognitive impairment has always been the single-most important side effect associated with ECT. Concerns regarding long-term cognitive impairment surfaced soon after the introduction of ECT and since then has grown to become one of the most controversial aspects of ECT. Anti-ECT groups have frequently pointed out to cognitive impairment following ECT as evidence of ECT causing brain damage. A meta-analysis by Semkovska and McLoughlin in 2010 is one of the most detailed studies which had attempted to settle this long-standing debate. The authors reviewed 84 studies (2981 participants), which had used a combined total of 22 standardized neuropsychological tests assessing various cognitive functions before and after ECT in patients diagnosed with major depressive disorder. The different cognitive domains reviewed included processing speed, attention/working memory, verbal episodic memory, visual episodic memory, spatial problem-solving, executive functioning, and intellectual ability. The authors concluded that administration of ECT for depression is associated with significant cognitive impairment in the first few days after ECT administration. However, it was also seen that impairment in cognitive functioning resolved within a span of 2 weeks and thereafter, a majority of cognitive domains even showed mild improvement compared to the baseline performance. It was also demonstrated that not a single cognitive domain showed persistence of impairment beyond 15 days after ECT.
Memory impairment following ECT can be analyzed broadly under two conceptual schemes – one that classifies memory impairment as objective memory impairment and subjective memory impairment and the other that classifies it as impairment in anterograde memory versus impairment in retrograde memory. Objective memory can be roughly defined as the ability to retrieve stored information and can be measured by various standardized neuropsychological tests. Subjective memory or meta-memory, on the other hand, refers to the ability to make judgments about one's ability to retrieve stored information. As described previously, it has been conclusively demonstrated that anterograde memory impairment does not persist beyond 2 weeks after ECT. However, one of the major limitations of this meta-analysis was the lack of evidence on retrograde amnesia following ECT. This is particularly unfortunate considering that it is memory impairment – particularly retrograde amnesia which has received the most attention. In addition, reports of catastrophic retrograde amnesia have been repeatedly held up as sensational evidence of the lasting brain damage produced by ECT. Admittedly, studies on retrograde amnesia are fewer and less conclusive than on anterograde amnesia., At present, the results are conflicting, with some studies finding some impairment in retrograde memory – particularly autobiographical retrograde memory up to 6 months after ECT.,,, However, more recent studies have failed to support this finding., While they do demonstrate an impairment in retrograde memory immediately after ECT, it was seen that this deficit returned to pre-ECT levels within a span of 1–2 months and improved beyond baseline performance at 6 months post ECT. Adding to the confusion are numerous factors which confound the assessment of retrograde amnesia. It has been shown that depressive symptoms can produce significant impairment of retrograde memory., It has also been demonstrated that sine-wave ECT produces significantly more impairment of retrograde memory as compared to brief-pulse ECT. However, from the 1990s onward, sine-wave ECT has been completely replaced by brief-pulse ECT, and it is unclear as to the implications of cognitive impairment from the sine-wave era in contemporary ECT practice.
Another area of concern are reports of subjective memory impairment following ECT. One of the pioneers of research into subjective memory impairment were Squire and Chace who published a series of studies in the 1970s demonstrating the adverse effect of bilateral ECT on subjective assessment of memory.,,, However, most of the studies conducted post 1980 – from when sine-wave ECT was replaced by brief-pulse ECT report a general improvement in subjective memory assessments following ECT. In addition, most of the recent studies have failed to find a significant association between measures of subjective and objective memory.,,,,, It has also been shown that subjective memory impairment is strongly associated with the severity of depressive symptoms. In light of these facts, the validity and value of measures of subjective memory impairment as a marker of cognitive impairment and brain damage following ECT have been questioned. However, concerns regarding subjective memory impairment and catastrophic retrograde amnesia continue to persist, with significant dissonance between the findings of different research groups and patient self-reports in various media.
Some studies reported the possibility of ECT being associated with the development of subsequent dementia., However, a recent large, well-controlled prospective Danish study found that the use of ECT was not associated with elevated incidence of dementia.
| Conclusion|| |
Our titular question is whether ECT leads to brain damage, where damage indicates destruction or degeneration of nerves or nerve tracts in the brain, which leads to loss of function. This issue was last addressed by Devanand et al. in 1994 since which time our understanding of ECT has grown substantially, helped particularly by the advent of modern-day neuroimaging techniques which we have reviewed in detail. And, what these studies reveal is rather than damaging the brain, ECT has a neuromodulatory effect on the brain. The various lines of evidence – structural neuroimaging studies, functional neuroimaging studies, neurochemical and metabolic studies, and serum BDNF studies all point toward this. These neuromodulatory changes have been localized to the hippocampus, amygdala, and certain other parts of the limbic system. How exactly these changes mediate the improvement of depressive symptoms is a question that remains unanswered. However, there is little by way of evidence from neuroimaging studies which indicates that ECT causes destruction or degeneration of neurons. Though cognitive impairment studies do show that there is objective impairment of certain functions – particularly memory immediately after ECT, these impairments are transient with full recovery within a span of 2 weeks. Perhaps, the single-most important unaddressed concern is retrograde amnesia, which has been shown to persist for up to 2 months post ECT. In this regard, the recent neurometabolic studies have offered a tentative mechanism of action of ECT, producing a transient inflammation in the limbic cortex, which, in turn, drives neurogenesis, thereby exerting a neuromodulatory effect. This hypothesis would explain both the cognitive adverse effects of ECT – due to the transient inflammation – and the long-term improvement in mood – neurogenesis in the hippocampus. Although unproven at present, such a hypothesis would imply that cognitive impairment is tied in with the mechanism of action of ECT and not an indicator of damage to the brain produced by ECT.
The review of literature suggests that ECT does cause at least structural and functional changes in the brain, and these are in all probability related to the effects of the ECT. However, these cannot be construed as brain damage as is usually understood. Due to the relative scarcity of data that directly examines the question of whether ECT causes brain damage, it is not possible to conclusively answer this question. However, in light of enduring ECT survivor accounts, there is a need to design studies that specifically answer this question.
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Dr. Shubh Mohan Singh
Department of Psychiatry, Postgraduate Institute of Medical Education and Research, Chandigarh
Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2]