What is the relationship between Obsessive Compulsive Disorder and other anxiety disorders?

Obsessive compulsive disorder (OCD) involves the recurrent intrusion of thoughts or mental images which are distressing and often inappropriate to the individual (such as wanting to kill a loved one), resulting in a need to suppress and neutralise them. This is attempted through the ritualised performance of repetitive compulsions, which can be either overt (such as repeated handwashing or checking) or covert (thinking the originally upsetting thought again a certain number of times). These actions are aimed at reducing the distress caused by the cognitions and at preventing the dreaded outcome. There are many similarities between OCD and other types of anxiety disorder, with all involving individuals who are more likely to interpret a situation as more dangerous than it really is, due to the particular assumptions and beliefs they learned during an earlier period of their lives. What makes OCD different, however, is the patients' overwhelming sense of responsibility for possible negative events, together with their belief that thoughts are equal to actions. In this way, OCD is a much more difficult disorder to treat, although cognitive and behavioural methods similar to those used with phobias and panic attacks have been found to be partially successful.

When considering OCD it is important to remember that intrusive thoughts are very common in the normal population (Rachman and de Silva, 1978), and that the disorder therefore lies on a continuum. As with most anxiety disorders, the difference between OCD and the non-clinical experience of distressing intrusions is in their interpretation. In Clarke's (1986) cognitive model of panic he suggested that it is the catastrophic misinterpretation of bodily sensations which causes and maintains panic attacks, and in a similar way, only those individuals who have an enduring tendency to interpret their own mental activities as indicating personal responsibility for future events, will experience the pattern of discomfort and neutralising that characterises OCD. Just as panic patients have been shown to focus on their internal sensations, thereby inadvertently increasing the probability of another attack, OCD patients have also been found to attend selectively to threat-related stimuli (Lavy et al, 1994), which may contribute to the number of obsessive thoughts they have.

Although OCD and other anxiety disorders clearly share the fact that stimuli, both internal and external, are misinterpreted as being more dangerous than they really are, there are also some striking differences between the disorders. In OCD the patient holds the unusual belief that there exists a fusion between her thoughts and actions, for example, if she thinks "I will kill my baby", she will then fear that this is actually going to happen just because she thought it. Even if the patient calculates that there is a very low probability of this danger occurring, the perceived cost is deemed too great to risk and neutralising behaviours are performed in order to prevent the possible negative outcome. In this way, compulsions can be compared with the safety behaviours undertaken by panic and phobia patients, in that they both reduce anxiety and prevent disconfirmation of the fears. In OCD, however, compulsive behaviours are a conscious attempt to exert control over future events, fuelled by a sense of responsibility for the outcomes, which is not present in other anxiety disorders. Evidence for the importance of responsibility appraisals in OCD comes from a study into the effects of changes in responsibility on compulsive checking (Lopatka and de Silva, 1995). It was demonstrated that decreases in perceived responsibility significantly reduced perceived discomfort, the urge to check, the probability and severity of anticipated harm and perceived panic. Although increases in perceived responsibility were not reliably followed by increases in checking behaviour, this may have been because responsibility was already so high that it could not be noticeably elevated, and the study clearly supports the role of responsibility in OCD. Interestingly, a decline in perceived responsibility was directly followed by a decline in the estimated probability the a misfortune would occur, implying that these are confused in the patients' minds.

Although intrusive thoughts are common, it seems that OCD patients find them more distressing and also experience them more frequently than the normal population, and it has been suggested that the patients' attempts to suppress the intrusive thoughts may actually contribute to maintaining the disorder (Clarke et al, 1991). Two hypotheses are possible explanations for this - suppression may lead to an immediate increase in the number of thoughts (enhancement), or suppression may be followed by a subsequent increase in thoughts (rebound effect). When this was tested by asking volunteers not to think about something for a period of time, no immediate enhancement effect was found but the evidence did support the rebound hypothesis. The subjects were very effective at suppressing thoughts in the short-term, but later the number of thoughts increased greatly. It may be the case, however, that enhancement does occur in individuals who are unable to use distraction while suppressing, such as OCD patients. In this way, the patients' strategy for reducing the distressing thoughts may actually increase them, thereby also increasing anxiety and the need for neutralising. Since compulsions relieve discomfort and anxiety, it has been proposed that they are reinforcing, in the same way that avoidance or escape is reinforcing in phobic patients. Rachman, de Silva and Roper (1996), studied the spontaneous decay of compulsive urges by provoking checkers to check, but then preventing them from performing their normal rituals. In this way they tested the hypothesis that compulsive rituals can as easily be anxiety provoking as anxiety reducing (Beech et al, 1969). They found that the execution of rituals reduced both the anxiety and the urge to check in all cases, contrary to Beech's proposal, and also found a spontaneous decay of discomfort and compulsive urges an hour after being prevented from neutralising. This strongly supports the exposure and response-prevention method of treating OCD, in which patients are exposed to a feared situation, such as touching "dirty" objects, and then prevented from carrying out their normal ritual in order to disconfirm their fears that something awful will happen.

Like with other anxiety disorders, there have been many attempts to link OCD to a biological factor. The seratonin hypothesis (Baumgarten and Grozdanovic, 1998), proposed that it is a deficiency in seratonin which causes OCD, but the only evidence for this is the efficacy of medication, such as clomipramine, which interferes with the uptake of seratonin. The time difference between the drug's effect on the nervous system and behavioural changes, however, suggest that it may not be seratonin itself that causes OCD but another unknown chemical on which it acts. The fact that SSRIs only result in a 50% improvement in OCD, and that a biological theory can not account for the effectiveness of cognitive behavioural therapy, further undermines a purely biological account of the disorder. There is some evidence, however, that a structural or functional dysfunction in the CNS may account for some aspects of OCD. Evidence for this comes from the finding that basal ganglia structures are associated with repetitive motor behaviour, and that this area may be damaged in OCD patients (Aylward et al, 1996). Saxena (1998) has also demonstrated that activity in the orbitofrontal cortex, caudate nucleus, thalamus and interior cingulate gyrus are implicated in OCD, suggesting that an imbalance of direct/indirect pathway tone in this circuit may mediate the repetitive, fixed behaviours relating to socio-terratorial concerns seen in OCD. Such a theory can not, however, account for the phenomenology of OCD, nor, like the seratonin hypothesis, for the success of CBT.

Treatment for OCD has mostly been of the cognitive-behavioural approach, and some of it has stemmed from methods successfully used to treat other anxiety disorders. Mowrer's 2 factor theory of phobias proposes that safety behaviours, such as avoidance or escape, become reinforced because they reduce anxiety, and therefore prevent the patient from seeing that their fears are unfounded. This theory has been applied to OCD by Rachman and Hodgson (1980), who suggested that the best method for treating the disorder is to expose the patient to the feared situation and then prevent them from performing their normal neutralising behaviours. In this way, it is hoped that the conditioning will be broken and the patient will no longer associate their obsessive thoughts with distress and anxiety. Although this is partially successful ( a 75% success rate was reported by Riggs and Foa, 1993), many OCD patients' fears are very far-fetched, such as fearing that they will burn in hell for all eternity if they do not neutralise their thoughts, and preventing them from performing their rituals may not actually disconfirm their belief that they will cause a terrible outcome. Cognitive behaviour therapy for OCD is therefore much less straight forward than for other anxiety disorders, some of which can be treated in a single session, and it aims to help patients step outside their concerns and adopt an entirely different perspective on their problem (Salkovskis, 1999). The main techniques used involve constructing and actively testing a coherent alternative and less threatening explanation of the patient's problem, and contrasting this with the one they had been applying themselves and that had been motivating their obsessive behaviour. In this way, patients are encouraged to conclude that obsessional thoughts are irrelevant to further action and that trying to control their thoughts is unnecessary and unhelpful.

Some of the misinterpretations the patient can be helped with are their over-estimations of the chance of danger occurring, as well as the extent of the consequences of the danger and their over-estimations of the amount of responsibility they hold and the perceived consequences of being responsible. A method often used is the pie-technique (Van Oppen and Arntz, 1994), in which a pie chart is filled with all the factors contributing to a negative event, with the patient's own responsibility filled in last. This helps the patient to realise how multi-faceted responsibility is and how they can not be solely responsible for any event. Another method used is the double-standard technique, in which the patient is encouraged to compare how they would perceive a negative event happening to someone else with how they would perceive the same event if it happened to them. Behavioural experiments can also be used to test out the empirical basis of being responsible and to identify and challenge the misinterpretations that cause the rituals in the first place. In general, these methods are quite successful in reducing the symptoms of OCD (Freeston et al, 1994) and they have an advantage over exposure response-prevention alone (van Oppen et al, 1995), but OCD is still one of the most difficult of the anxiety disorders to treat.

In conclusion, OCD relates to other anxiety disorders in that they all involve excessive ruminations about future catastrophes, and they all fit into a cognitive model in which safety behaviours, such as avoidance in phobias, sitting down in panic attacks and neutralising compulsions in OCD, are reinforced due to their anxiety-reducing effects and therefore prevent the disconfirmation of fears. OCD is, however, differentiated from other anxiety disorders by the perception of responsibility for negative outcomes, and the ritual behaviours which characterise the disorder can therefore be seen as a conscious attempt to either overtly or covertly prevent those outcomes from occurring.