To avoid or not to avoid, that’s the question. The relationship between pain-related avoidance behaviour, pain-related fear, and pain reports

Why is it that some people develop chronic pain after an injury, while others don’t? Pain has a clear function for our survival, because it signals potential harm or danger to the body and it promotes behaviours, such as avoidance and escape, to protect ourselves against these dangers. However, pain could also become a false alarm, especially in the case of chronic pain, where there is often  no objectifiable injury and where pain is disconnected from its original function.

Avoidance is considered key in the development and maintenance of chronic pain. Fear-avoidance models propose that pain-related fear may spur avoidance behaviour leading to chronic pain disability. So far, the fear-avoidance model assumes a unidirectional relationship between pain-related fear and avoidance, i.e. pain-related fear evokes avoidance behaviour. However, little is known about how avoidance behaviour subsequently affects pain-related fear and pain. In this PhD research project we introduced a new line of experimental work to further investigate the relationship between pain-related avoidance behaviour and pain-related fear. In a series of studies we have experimentally manipulated (the perception of) avoidance behaviour and tested its effects on changes in fear and pain reports. The results of our studies indicated that engaging in avoidance may (paradoxically) increase rather than decrease pain-related fear (i.e. bidirectionality hypothesis, whereby pain-related fear leads to avoidance behaviour (one direction) and in turn, engaging in avoidance behaviour increases pain-related fear (other direction)).

In our first study (see chapter 2) we tested the effects of avoidance of a painful heat stimulus on pain-related fear and pain. The results showed that self-reported pain-related fear was higher after performing an avoidance response (pressing the stop-button), despite equal intensities and duration of the heat stimulus as in the control condition. In our second study (see chapter 3), where we also tested the effects of avoidance of a painful heat stimulus, we replicated the findings of the first study, whereby we observed higher pain-related fear levels when the avoidance response was no longer available compared to those when the avoidance response was available. We also found that perceived avoidance attenuates pain reports despite exposure to identical stimulus intensity. In addition, the results showed that increased threat appraisals mediated the relationship between avoidance behaviour and increased pain-related fear. Together, these results provide support for a bidirectional relationship between fear and avoidance.

Chapter 4 describes our third experimental study, where we examined motor-behavioural characteristics of avoidance behaviours during different movements, using the HapticMaster, a 3-degrees of freedom, force-controlled robotic arm. We investigated the changes in pain-related fear and pain when avoidance behaviour was no longer effective. The results indicated participants became more afraid of and sensitive to pain, when previously acquired avoidance behaviour was no longer effective. Also, participants continued to show avoidance behaviour despite it being not adaptive anymore. These findings suggest that ineffective avoidance may play a role in the development and maintenance of chronic pain.

In our fourth experimental study (see chapter 5), where we also applied a robotic arm-reaching task, we investigated whether performing a movement to avoid a painful stimulus in the context of a novel, ambiguous movement increased threat and pain-related fear towards this movement, and whether avoidance behaviour persisted when given the choice between performing the acquired movement to avoid a painful stimulus or an alternative, novel movement. The results revealed that acquired avoidance behaviour in the presence of a novel, ambiguous movement elevated pain expectancy and pain-related fear towards that novel movement, even in the absence of confirmation of the actual threat level of the novel movement. We also observed persisting avoidance behaviour towards the novel movement, thereby preventing disconfirmation of the novel movement threat appraisals. These findings suggest that avoidance in the context of other neutral activities/movements may lead to the development and maintenance of threat appraisals and irrational fears.

Taken together, the findings reported in this dissertation provide support for the bidirectional relationship between pain-related fear and avoidance and constitute an important step in furthering our understanding of the underlying mechanisms in the development and maintenance of chronic pain.