The relationship of alexithymia to pain severity and impairment among patients with chronic myofascial pain

Abstract

Objective: Alexithymia is elevated among patients with chronic pain, but the relationship of alexithymia to the severity of pain among chronic pain patients is unclear. Also, studies have rarely examined whether alexithymia is unique from other, more widely studied constructs in the chronic pain literature (i.e., self-efficacy, catastrophizing, and depression), and research has not examined how alexithymia relates to the sensory versus affective dimensions of pain. Methods: Among 80 patients with chronic myofascial pain, we tested how alexithymia (Toronto Alexithymia Scale-20) was related to three competing constructs—self-efficacy, catastrophizing, and depression—and to the sensory and affective dimensions of pain as well as physical impairment. We then determined whether alexithymia remained correlated with pain and impairment when tested simultaneously with each of the three competing constructs. Results: Analyses controlled for patients' sex, age, marital status, and duration of pain. Alexithymia was moderately correlated with less self-efficacy and greater catastrophizing, and substantially correlated with greater depression. Alexithymia was positively related to both affective pain and physical impairment, but was unrelated to sensory pain, whereas all three of the competing constructs were related to both types of pain as well as physical impairment. Regression analyses indicated that alexithymia remained a significant and independent correlate of affective pain severity while controlling for either self-efficacy or catastrophizing, but depression accounted for alexithymia's relationship with affective pain. Also, alexithymia was no longer related to physical impairment, after controlling for any of the other three constructs. Conclusion: Although alexithymia is not related to the sensory component of pain, it is correlated positively with the affective or unpleasantness component of pain, independent of self-efficacy or catastrophizing. The emotional regulation deficits of alexithymia may lead to depression, which appears to mediate alexithymia's relationship to affective pain. Alexithymia's relationship with physical impairment appears to be better accounted for by self-efficacy or catastrophizing.

Introduction

Alexithymia is conceptualized either as a deficit in a person's ability to employ cognitive processes to identify, differentiate, and communicate one's affective states [1], or as a global impairment in conscious recognition of emotion [2]. Alexithymia is thought to impede successful regulation of emotions, particularly negative affects, resulting in chronic sympathetic hyperarousal, physiological sensations, somatosensory amplification, and complaints of physical symptoms [3].

Alexithymia is elevated in numerous psychosomatic, psychiatric, and medical conditions [1], [3]. In particular, studies have found elevated alexithymia among patients with chronic or persistent pain. For example, from one-third to 53% of patients with various types of persistent pain appear to be alexithymic [4], [5], [6]. These percentages appear to be much higher than the base rate of alexithymia, which has been supported by studies that have included nonpain comparison groups. These studies have found higher levels of alexithymia among patients with psychogenic pain [7], rheumatoid arthritis [8], and inflammatory bowel disease [9] than among controls. Our group found that alexithymia was greater among a sample of heterogeneous chronic pain patients than among patients seeking treatment for either obesity or nicotine dependence [10].

It is noteworthy, however, that in all of these studies, only about one-quarter to one-half of the chronic pain patients had elevated alexithymia scores, suggesting that there is much variability in alexithymia among people with chronic pain. Similarly, there are substantial individual differences in pain severity and disability among those with persistent pain. Some people report little pain and have minimal disability, whereas others complain of great pain and dysfunction. This raises the possibility that differences in alexithymia account for variations in the experience of pain and disability. Yet, the evidence for this is mixed. In support of this hypothesis, three studies of healthy people found that alexithymia was positively correlated with reported pain during experimental pain induction or during medical procedures [11], [12], [13]. In contrast, three studies of relatively large samples of patients with various chronic pain conditions found no relationship between alexithymia and pain severity [4], [5], [6]. Thus, it remains unclear whether alexithymia is associated only with the presence of chronic pain per se, or is also associated with the severity of pain and disability among people with pain.

A recent editorial argued that research on alexithymia and specifically on the most widely used instrument, the Toronto Alexithymia Scale-20 (TAS-20), needs to be advanced by simultaneously considering other constructs that might compete with alexithymia as predictors of clinically important criteria, and by determining what alexithymia does not predict [14]. Most research studies have assessed only alexithymia as the sole predictor of some criterion measure, without also reporting other competing predictor constructs. It is important to determine whether alexithymia is unique in its ability to predict a criterion, whether another measure predicts the criterion better, or whether another measure mediates alexithymia's relationship with a criterion. Second, most alexithymia studies have reported only what alexithymia is related to or predicts, but not what it is unrelated to. Yet, the process of determining a measure's discriminant validity is a necessary complement to determining its convergent validity.

In this study, we sought to compare alexithymia to three widely studied predictor constructs in the chronic pain literature: self-efficacy, catastrophizing, and depression. Self-efficacy is the belief that one has the capacity to control pain and functioning in one's daily activities. Pain-related self-efficacy is one of the most robust predictors of reduced pain and disability and better adjustment across a range of measures [15], [16], [17], [18], [19]. One might hypothesize that alexithymia is related to reduced self-efficacy, but this has not yet been tested.

Catastrophizing also has been widely studied in the pain literature, and it is defined as the tendency to focus on and exaggerate the threat value of painful stimuli and to negatively evaluate one's ability to cope with pain [20]. Many studies have demonstrated that catastrophizing is related to a number of pain-relevant outcomes, including higher reported pain [21], [22], more overt pain behaviors [23], and more disability [22], [24]. Like self-efficacy, catastrophizing also has not yet been studied in relation to alexithymia, but alexithymic people may be more prone to catastrophize, given the negative affective experience associated with both of these conditions.

Finally, depression has been widely studied in both the chronic pain and alexithymia literatures. Chronic pain is often comorbid with depression [25], [26], and alexithymia is also substantially related to depression and may predispose to it [1], [3]. These observations suggest that depression may mediate the relationship between alexithymia and chronic pain. Indeed, recent research by Kosturek et al. [27] found that when depression was taken into account, alexithymia became unrelated to chronic pain, and de Zwaan et al. [28] found that depression, but not alexithymia, influenced thresholds to thermally and mechanically induced pain among patients with eating disorders.

This study also sought to examine both the convergent and discriminant validity of alexithymia by differentiating two types of pain. Pain is not a single entity, but includes at least two dimensions. The International Association for the Study of Pain [29] defined pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.” The sensory component of pain refers to its intensity and patterning. It might be thought of as the “volume” of pain stimulation. In contrast, the emotional or affective component of pain can be thought of as the degree to which a person experiences unpleasantness. Differentiating these two dimensions is important because they are affected by different psychological and biological processes [30]. For example, psychosocial treatments and medications that alter emotional functioning generally influence pain's affective dimension more than sensory dimension. The affective pain dimension appears to be regulated by the limbic system, whereas the sensory pain dimension is not. No prior studies of alexithymia have differentiated these two types of pain, but we hypothesized that alexithymia, which involves impaired emotional regulation, should be related to the affective component of chronic pain, but not to the sensory component of pain.

This study had three primary goals. First, in order to better understand the construct validity of the TAS-20, we examined how it was related to three widely studied constructs in the pain literature—self-efficacy, pain catastrophizing, and depression—the first two of which have not previously been examined in relation to alexithymia. Second, we tested whether alexithymia is related to the affective but not the sensory component of pain, and we also included a measure of pain disability or physical impairment as a criterion because it remains unclear whether alexithymia is related to impairment. Third, we tested whether alexithymia had unique predictive validity for pain severity and impairment—accounting for variance in these criteria beyond that explained by the more widely studied constructs of self-efficacy, catastrophizing, or depression—and whether depression might mediate the relationship between alexithymia and pain severity. We also explored separately how each of the three facets of alexithymia, as measured by the TAS-20, is related to the other predictors and to pain severity and impairment. We examined these relationships in a sample of patients with chronic myofascial pain, a group of interrelated muscular pain disorders that includes fibromyalgia and that are ranked among the most frequent causes of chronic pain [31].