Contrary to our expectation and in seeming contradiction to our previous cross-sectional analysis in the same cohort25
, this prospective study showed a negative rather than a positive association between alexithymia and occupational LBP, particularly for the factor “difficulty describing feelings”. From our previous cross-sectional and this new prospective study a paradoxical set of findings emerges: Reduced emotional awareness was associated with an increased 1-year prevalence of self-reported LBP in the cross-sectional analysis and a decreased incidence of compensated LBP claims in the prospective analysis. Several considerations are presented to understand these paradoxical findings.
First, we have to consider the validity of the TAS-20 instrument in assessing the ability to put one's emotion into words. The items for the factor “difficulty describing feelings” (factor 2 of TAS-20) do not distinguish the difficulty in symbolizing emotions from the difficulty in communicating emotions; in fact, they were only weakly or not at all associated with the observation-based Levels of Emotional Awareness Scale (LEAS).46, 49
Instead, they were strongly associated with shame anxiety (Corr. = 0.58) and shyness-embarrassment (0.69)50
. Our findings might therefore reflect fears of being ashamed and of self-devaluation in communicating emotions rather than difficulties in symbolizing emotions as the basis for the difficulty in emotional self-disclosure in social interactions50
Second, in previous cross-sectional research alexithymia was associated with increased symptom reporting68
. Alexithymia has previously been found to be stronger related to subjective pain and complaints of symptoms than to physical functioning and disability42, 68
. Our results seem to show a similar pattern, with alexithymia positively associated with self-reported LBP symptoms but not or negatively associated with compensated work disability from LBP.
Third, findings regarding the prevalence of self-reported LBP symptoms are not readily comparable to findings regarding the incidence of compensated LBP claims, even within the same study population. Filing a claim and receiving compensation is at least two steps removed from experiencing LBP symptoms. One possible interpretation is that the proneness or willingness to or the efficacy in filing a claim and navigating the bureaucratic process, rather than the onset of symptomatic LBP, might be negatively associated with the difficulty describing feelings. Or in other words: if one is less able to describe one's feelings, could one also be less apt and able or willing to complete the somewhat cumbersome process of filing a claim or convincing the examining physician of one's predicament? Recalled or present, the experience of LBP, the degree to which it is disabling, and the capacity or need of filing a claim are discernable consecutive steps in a chain of events, and personality traits can have different and maybe even opposite effects at each step.. Such time-dependent or “disability phase-specific” effects have been shown in a cohort of Californian low back pain claimants examining psychosocial and physical job factors.69, 70
Consequently, a possible interpretation of the result of this study is that the fear of being ashamed and self-devaluated, the shyness and anxiety around verbally expressing emotions is associated with a decreased willingness to file a claim with workers' compensation for a LBP injury. Thus the difficulty identifying feelings can be positively associated with recalled LBP prevalence, which is strongly predictive of LBP later on, but the difficulty in expressing emotions from fear of being ashamed may negatively modify the efficacy in successfully filing for workers' compensation.
The independent negative association between alexithymia and LBP incidence becomes stronger after controlling for the coping-with-stress strategy of denial. Denial of stress has a strong positive association with the incidence of compensated claims (separate publication in preparation). Denial and alexithymia are moderately and positively correlated (r = 0.38) but they seem to have opposite effects on LBP claim incidence. Alexithymia and denial are not mediators for each other, as including one of these variables to a model using the other as predictor strengthens rather than weakens the effect of the predictor on the outcome (Sobel-Goodman tests: negative value). Furthermore, they are not effect modifiers to each other as their product terms are not significant (P = 0.91). Rather, they are negative confounders to each other and mask each other's effect on the outcome.
Drivers with difficulties describing feelings likely also have difficulties identifying feelings (r = 0.68). One possible interpretation is that they might be more willing to complain about LBP in the past year and prefer to ignore the actual stress of it and avoid the stress of going through the hassles involved in filing a claim, in-line with a strategy of denial and disengagement.
A secondary aim of the study was to answer the question whether alexithymia might be a risk factor for the chronification of compensated LBP. We found that among workers filing a first claim for LBP, duration of work disability associated with this claim was unrelated to alexithymia.
Again, as reported in previous cross-sectional studies of different samples and diagnoses25, 42, 43
, ethnicity seems to play an important role for the effect of alexithymia on health outcomes and its role remains to be explored. Our findings from both cross-sectional and prospective analyses consistently contradict reports suggesting that variations in emotional awareness and expression may be more important for pain reports among African Americans than among Caucasians42
The major strength of this study is its prospective design, its relatively large sample size compared to the smaller samples used in alexithymia research, its ethnical diversity, and our ability to control for several important psychological and workplace factors.
A major limitation of this study is that depression or negative affect were not separately assessed. Both factors are associated with alexithymia30, 71, 72
particularly when assessed by TAS-2046
and are associated with low back pain as well22, 30, 73-75
. Depression and alexithymia scores have been reported as being correlated (Pearson) at 0.40 to 0.59 76
. Several studies found an effect of alexithymia on symptom report even after controlling for depression: Alexithymia predicted self-report of somatic symptoms in depressed patients 77
, independently from depression78
, and remained stable among depressed patients when level of depression declined79
. Furthermore, the association between a distinct neuro-endocrine pattern and alexithymia was strengthened in men after controlling for depression80
. However, depression has also been suggested to mediate the association between alexithymia and the affective component of chronic myofascial pain30, 81
or symptom complaints in somatoform disorders46
. These latter studies found no additional contribution of alexithymia when controlling for depression but persistent contribution of depression when controlling for alexithymia: alexithymia, interfering with adaptive emotion regulation, resulted in negative affect such as depression, which in turn influenced the affective pain experience30
. These findings suggest that depression may be a mediator between alexithymia and the affective component of pain. In this case, adjustment for depression would be a methodological mistake.
The primary predictor variable alexithymia used for this report was collected by self-assessment. Observation- or performance-based measures, such as LEAS, clearly would be preferable. However, this was not feasible in such a large sample.
Respondents tended to be proportionally more men, less African-American, more light rail and less diesel-bus drivers. Therefore, our ability to generalize our findings to all San Francisco municipal transit operators is limited. However, since we controlled for vehicle type and ethnicity in our analyses and response rates were rather high we feel confident that our findings were not materially influenced by any response bias. The observed variation of effects across ethnical groups may have several explanations. In order to examine them it will be necessary to validate the concept and measurement of alexithymia (and of LPB for that matter) for different ethnic groups.
Our results did not confirm previously reported findings of a positive association between deficiencies in emotional awareness and LBP, at least regarding the incidence of work-related, compensated claims of LBP injuries with workers' compensation insurance. To the contrary, high alexithymia may reduce the incidence of such claims, at least among Caucasians. One plausible explanation in light of the literature is that shame rather than level of emotional awareness explains the discrepant findings in our cross-sectional and prospective studies.
Also, we found no positive relationship between alexithymia and duration of disability or the incidence of chronic disabling compensated LBP. This does not entirely rule out the possibility of alexithymia being a risk factor for non-disabling LBP when no formal insurance claim is filed and compensated, i.e. in a primary care clinic rather than occupational setting. The latter is a different outcome and may have different predictors.
As in our previous report25
, this study again demonstrated the importance of including coping styles in analyses of alexithymia and LBP. We will report separately about the relationship of coping styles with LBP.