The study at hand found many indices to be statistically significantly different between HCG and OCD group, regarding both WCST and ToL. These indices denote that EF deficits are in fact related to OCD.
In WCST, namely, total number of perseverative errors, means number of perseverative errors, total number of non-perseverative errors, and means numbers of non-perseverative errors were found to be significantly different and were most important in interpretation of EF deficits. Higher perseverative errors in the OCD group denote failure of set shifting, while higher non-perseverative errors could indicate rapid loss of information learnt during the previous trials in the course of the test; denoting problems with working memory.
Sanz et al. stated that the most consistent finding across the studies in OCD was the deficit in tasks involving shifting in cognitive set. The cognitive operations needed to perform the WCST, searching for a new category and the consolidation of the correct classification category, were closely related to shifting cognitive set [14].
In ToL, only the total time, but not the total number of moves, was found to be statistically significantly different between HCG and OCD group, which could indicate a milder form of impairment in planning ability, response inhibition, and reasoning.
Abramovitch and Cooperman reported similar to the present results that there was significant difference in planning ability between healthy individuals and OCD individuals; being reduced in the latter, as measured by excessive moves in ToL and Tower of Hanoi (ToH) tests [15].
Also, in consistency with the current study, the study of Bouvard et al., in which the Behavior Rating Inventory of Executive Function Adult (BRIEF-A) was used to measure executive dysfunction in everyday life in people with OCD, their results confirmed the impairment of EF for patients with OCD [16].
Goncalves et al. reported poor performance in both attentional set shifting and task-switch situations in individuals with OCD in comparison to healthy individuals. This was evident by significantly more errors by OCD individuals [17].
Page et al. concluded that there was consistent evidence that OCD patients tend to decrease their working memory performance with increase task load [18].
In addition, the study of Pedroliet al. involved 58 participants (29 OCD patients and 29 controls) and showed a clear difference was found between OCD patients and the control group, particularly in EF [6].
It is however worth mentioning that, in the current study, not all indices were statistically significantly different between the individuals of both groups, which can shed some light on the wide variations and inconsistency in literature regarding EF deficits in OCD patients; the types, magnitude, and underlying pathology. This might be due to the fact that there’s a wide range of EF tests with wide range of calculated indices of which the application and interpretation can differ between researchers in literature.
For example, Shin et al. reported that patients with OCD appear to have broad, albeit not severe, EF deficits. Although the magnitude of the deficits was, in general, not large, visuospatial memory, visual organizational skill and, in accordance with the present results, planning ability appear to be the most impaired areas in patients with OCD. They also reported similarly to the current study that individuals with OCD had been observed to experience difficulties in (1) inhibiting ongoing cognitive and motor responses, (2) shifting attention from one aspect of stimuli to others, (3) engaging in executive planning, and (4) decision-making [5].
Other authors, like Bedard et al., mentioned that patients with OCD to experience significant impairments in visuospatial memory, verbal memory, verbal fluency, and processing speed, whereas the attentional ability was relatively preserved [19].
Meanwhile, Bannon et al. mentioned that the inconsistency in literature findings at many levels, regarding EF impairments in OCD patients. For example, it was reported by some authors that the most consistent finding was a deficit in inhibition and impaired set shifting ability, while planning ability was reported to be unaffected. Inconsistent findings had been observed for working memory and verbal fluency [20].
Similarly, Hosenbocus and Chahal reported that findings on working memory and verbal fluency had also been inconsistent. On the one hand, adolescents with OCD had been reported to have deficits similar to patients with frontal lobe lesions. On the other hand, other authors reported no impairments on several measures of working memory. Similar inconsistencies were reported in children with OCD. Interestingly, some authors reported that children with OCD demonstrated relative strengths in various executive control domains as well as intact memory functioning in comparison to HCG [1].
On the other hand, other neurocognitive conclusions as Bedard et al. tended to be moderate, as impairments might in fact be limited to basic functions such as motor execution and speed of processing [19].
Literature had also revealed mixed findings regarding EF deficits pathophysiology. For example, set shifting and inhibition were considered by some authors as Moritz et al. to represent deficits in core EFs; such that, a deficit of planning measured at the ToL or a low score at the WCST, associated with dorsolateral frontal lesions, might in fact reflect low motor inhibition or poor set-shifting capacities, respectively, more closely associated with frontal ventral or caudate involvement [21].
Divergent results from previous studies might be explained by the fact that OCD is a complex disorder with many symptoms and variants.
Regarding the relation between OCD symptoms severity and EF, this study showed that there were significant relation between OCD symptoms severity and EF in some domains.
In consistent with Fournet et al. who revealed positive significant correlations between the measures of OCD severity and BRIEF-A main scores [4]. Also, the results of McNamara et al. who found in children with OCD that impairments in various domains of EF were predictive of higher mean obsessive compulsive severity scores [22].
Pedron et al. showed that specific impairment of EF was associated with specific obsessive-compulsive symptoms dimensions (e.g., symmetry/ordering, hoarding, contamination/cleaning), the severity of obsessive-compulsive symptoms in those different dimensions significantly correlating with impaired specific EF [23].
This association between EF impairment and symptoms severity could be explained by the frontosubcortical circuitry deficits in OCD, influencing both clinical symptoms and executive dysfunctions, creating a vicious circle [4].
In a large systematic meta-analytic review of correlations between cognitive function and symptom severity in OCD samples. Thirty-eight studies were included; they found a small-to-moderate degree of association between OCD symptom severity and cognitive function [24].
In contrast, Bédard et al. assessed the EF of 40 patients with OCD and did not found correlation between the severity of illness and neuropsychological findings [19]. Similarly, in another study conducted by Airaksinen et al. who mentioned no correlation between neuropsychological test scores and YBOCS scores of patients with OCD [25].
Several studies have suggested significant association between the severity of symptoms and neuropsychological deficits in OCD. However, other studies have reported the absence of association between symptoms and neuropsychological test performance [26].
The study at hand also showed that there was no statistically significant difference between patients who had been receiving treatment accompanying OCD and those who had not regarding EF as evident by both WCST measured parameters and TOL parameters.
In consistent with Fournet et al. who revealed an impairment in EF in the treatment-naïve and relapsed OCD groups, relative to the HCG with no significant difference in EF between the two groups of patients [4].
Authors have argued for the absence of significant effect of medications. A study with large number of drug-naïve OCD patients reported significant impairment in tower of London, further supporting the primary nature of deficits and absence of significant effect of medications [27]. On the contrary, few studies have suggested improvement in neuropsychological test performance after treatment with selective serotonin reuptake inhibitors [28].
As regards OCD and comorbidities, the present results showed no statistically significant difference between patients who had comorbidities accompanying OCD and those who had not regarding EF as evident by both WCST measured parameters and TOL parameters.
Only a few studies have specifically examined the effect of depressive symptoms on neuropsychological performance in OCD; one study compared patients with OCD and those with unipolar depression and reported greater cognitive deficits in OCD compared to unipolar depression [29].
In agreement with Abramovitch et al. who examined the relationship between severity of depression and neuropsychological performance. This meta-analysis did not suggest significant relation between depressive symptoms and neuropsychological performance in OCD [30].
Further, evidence for persisting neuropsychological deficits in recovered OCD patients in the absence of depression or anxiety which provides further support to the view that these deficits are primary to OCD and not secondary to depression or other comorbidities [31].
On the other hand, Moritz et al. have found differences in WCST and creative verbal fluency test scores between OCD patients with high Beck Depression Inventory and Hamilton Depression Rating Scale (HAM-D) levels, OCD patients with low Beck Depression Inventory, and HAM-D levels and healthy controls. Executive functions of patients with OCD with low depression levels were found to be similar to those of healthy controls [32].
The limitations of present study included that assessment of EFs using WCST represents some domains of EFs but not all that is why there is an immediate need for uniform assessments in OCD as at present, there are no guidelines or consensus on the tests to be used. Such a consensus cognitive battery could allow cross-cultural comparison of results and could be used in future for multicentric trials for prediction of treatment response. Also, the small sample size may affect our results. Difficulty to identify patients in the clinic without comorbidity and without use of medicines forced us to include those patients on our study. It may be suggested that additional studies are needed, conducted over larger patient groups without comorbidity and use of medicines and where subgroups of disorders are taken into consideration to overcome the existing contradictory results in this field.
