Fibromyalgia has been described as a chronic condition characterized by widespread musculoskeletal pain, sleep disorders and prominent fatigue [1]. The prevalence of fibromyalgia as a rheumatic disease has shown to be between 0.2 and 6.6% in the general population, between 2.4 and 6.8% in women and between 0.7 and 11.4% in urban areas [2]. Worldwide, researchers are still debating on the as yet unclear etiopathogenesis of fibromyalgia which could comprise genetic predisposition, environmental factors, an influence on the neuroendocrine functions and the contribution of immune system [3]. A recent work [4] revealed how certain gene polymorphisms (especially those influencing serotoninergic, dopaminergic and catecholaminergic systems) could be directly involved in fibromyalgia development, with an influence on susceptibility and symptoms severity. Jiao and colleagues [5] observed the role of physical trauma and infection as a precipitating factor, while another study [6] suggested that regulation of pain process can be influenced by viral or bacterial infection throughout the activation of a specific type of cytokines. In his critical review, Di Tella M, et al. [7] highlighted that central sensitization could play an important role in fibromyalgia syndrome; in fact, the high sensitization to noxious stimuli can lead to hyperalgesia or allodynia and equate different clinical conditions (central sensitivity syndromes). In a recent review [8] fibromyalgia has been described as a central sensitization syndrome characterized by chronic widespread pain. There are other factors that could influence both the onset and the course of fibromyalgia: Eating habits, psychic stress response (as a psychological variable) and lack of social relationships [9]. Nevertheless, patients suffering from this condition have to deal with heterogeneous symptom manifestations, non-resolving treatments and a high prevalence of comorbidity suggesting a complicated diagnostic process [9]. Fibromyalgia often occurs in comorbidity with psychiatric conditions of various kinds, including mood disorders and anxiety disorders [10-13]. Specifically, some studies highlighted high percentages of major depression (comorbidity rates range from 20 to 80%), dysthymia and Generalized Anxiety Disorder [14-16] in FM patients.

The method used for this review satisfies the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) [30]. We identified PsycInfo and PubMed as databases for our research and selected fibromyalgia and personality as specific keywords, combined with the Boolean operator and. Specific inclusion criteria were as follows: a) the article was written in English and b) published in peer review journals, c) from 2010 to 2017 (the time span was selected based on the recent changing of international diagnostic criteria for fibromyalgia). Initially, the research returned a total number of 366 articles: From this opening corpus we deleted duplicated articles and corrigendum (n=12). At this stage some specific keywords were used to refine the results, in particular the Boolean operator not, to exclude articles about:

• adolescents (n=37),
• treatment and treatmentoutcome and pharmacologicaltreatment (n=99)
• psychometricproperties of evaluation instruments or questionnaires (n=124)
• etiologic aspects of rheumatic diseases and singlecasestudies (n = 29)
• other rheumaticdiseases and comorbidities (n=41).

The final number of articles enrolled in this study was 24, of which the full texts were examined independently. We decided to exclude a review about borderline personality disorder [31] in fibromyalgia because of its focus on a specific psychopathological disorder, a meta-analysis about the use of Minnesota Multiphasic Personality Inventory (MMPI) [22] in patients with fibromyalgia for its focus on a specific instrument and, lastly, a letter to the editor about perfectionism [32]. The articles examined for this systematic review were definitively 21. (Table 1). Fig. (1) presents a flow chart depicting the literature search process.

Fig. (1). Flow chart for literature search and screening results.

1. Regarding Definition and Diagnostic Criteria of Fibromyalgia Twenty studies [2, 3, 5, 6, 19-26, 28, 29, 33-41] defined fibromyalgia as a syndrome characterized by chronic widespread pain and sensitivity to digital palpation and only one study referred to fibromyalgia as a rheumatic disease [35]. Nineteen of these studies [2, 3, 5, 6, 19, 23, 25, 26, 28, 29, 33-41] add to this basic definition the presence of fatigue, sleep disorders, cognitive impairment and emotional distress. Furthermore, 5 studies [5, 19, 29, 35, 36] highlighted the presence of sensitivity to tender points (11/18) as described by ACR criteria for FM diagnosis in 1990 [21] while only two studies referred explicitly to the new ACR criteria [13] for its definition and diagnosis. From a methodological perspective, all studies enrolled participants who had been diagnosed with FM: In particular, 7 studies [5, 19, 24, 26, 33, 34, 41] recruited participants among those who had been diagnosed by expert rheumatologists and fibromyalgia hospital unit outpatients. In three studies [35, 36, 39], participants were selected from previously used databases. Ten studies clearly used the ACR criteria to select participants with FM; in one study the participants were described as people who meet the ACR criteria, without other specifications [37], 7 referring to ACR criteria of 1990 [2, 3, 6, 23, 25, 29, 39] and only 3 used the 2010 criteria [28, 38, 30].
2. Regarding Aspects of Personality The examined studies focused on various aspects of personality associated with FM and highlighted different roles for these aspects compared to FM. Five articles used the term “personality traits” to identify specific psychopathological elements in FM patients, pointing out the role of personality disorders, anxiety, depression as characteristics of a subgroup of patients [35-37, 40, 41]. Other studies examined some specific personality traits such as alexithymia, type D personality, emotional regulation, neuropsychological aspects and dysfunctional beliefs, and used a comprehensive model of personality such as that of Eysenck, Cloninger or the big-five model.

As far as neuropsychological aspects are concerned, three studies of the present review focused on this aspect [19, 26, 29]. The reasoning of the authors concerned the complex relationship between the comprehension and regulation of emotional states and the neurological networks that operate the ability required for social cognition. From the authors’ point of view, this executive function related to planning, working memory, attention and inhibition could possibly explain the hypersensitivity to pain and the difficulties in emotional recognition and regulation. Di Tella et al. [34], starting from the model of Miyake et al. [42], explained the subcomponents of Executive Function (EF) evaluating the social-cognitive profile of patients with FM and the relationship between the performance on cognitive tasks with that on social tasks. Results showed a significant impairment in social cognition skills in people with FM who highlighted at the same time a substantial independence of this impairment from executive function deficits. Miró et al. [43] explored the relationship between attention functioning and the main symptoms of FM with differences between genders and with healthy controls in three attention networks (alertness, orienting and executive control). Findings revealed a general impairment in attention networks for these patients, similar in both males and females. Rosselló et al. [44] evaluated the autonomic and central nervous response during affective startle modulation using the motivational priming hypothesis. They found out that patients are characterized by relevant impairment in affective modulation in response to affective state induction and they suggested the presence of alterations in both attentional and emotional aspects of information processing that could explain the main symptoms of FM.

Five studies examined alexithymia in FM patients [5-7, 17, 20]. Alexithymia has been described as a personality trait that includes difficulty in identification and description of emotions and feelings, together with an externally oriented cognitive thinking style [45]. The Toronto Alexithymia Scale (TAS-20), a self-report 20-item questionnaire, was chosen as the fundamental measure of alexithymia in all of these studies [45].

Di Tella et al. [35] examined the relationship between alexithymia and pain (both sensory and the affective component of pain) in 159 patients with fibromyalgia. The study showed that alexithymic patients exhibited higher level of pain intensity and pain experience (both sensory and affective dimensions) when compared to non-alexithymic ones (controls). Moreover, alexithymic patients showed higher levels of anxiety, depression and emotional distress compared with controls: When controlling anxiety, depression and emotional distress, no correlation was found. Emotional distress was the only predictor on intensity of pain and neither anxiety/depression or alexithymia showed a significant role in pain intensity.

The study of Montoro and del Paso [27] revealed that FM patients show higher levels of alexithymia compared with the healthy control group. Similarly, in Martinez et al. [41] alexithymia was shown to play an important role in predicting the affective aspects of pain. The study found FM group more alexithymia than in controls and when anxiety, depression and pain appraisal variables were controlled, alexithymia lost meaningfulness as a predictor of pain experience and sleep quality. On the other hand, anxiety demonstrated to be highly qualified in predicting pain experience, as depression was the best choice for sleep quality. Difficulty in identifying emotions has proved to have a moderate role in the relationship between pain catastrophizing levels and anxiety. Di Tella and colleagues [24] showed higher levels of alexithymia in FM sample compared with controls; moreover, a positive correlation between alexithymia, anxiety, depression and pain was found.

Ablin, et al. [28] showed two different personality profiles in a fibromyalgic sample: The first was characterized by higher well-being, more adaptive coping strategies and lower levels of alexithymia with a similar prevalence of type D personality when compared with the general population; the second qualified with lower levels of well-being, less adaptive coping strategies, higher levels of alexithymia and more prevalence of type D personality.

Moreover, the author assessed personality aspects from a psychobiological point of view. Van Middendorp et al. [46] found that on this peculiar type 56.5% of FM patients showed distressed personality while type D was associated with mental and physical health.

Specifically, the negative affective component was strongly related to the mental health of the sample and type D personality appeared highly prevalent in this group. In their contribution, Ablin and colleagues [28] studied the role of alexithymia and type D personality in fibromyalgia and chronic fatigue syndrome, and found in some patients maladaptive profiles with high level of alexithymia and high frequency of type D personality. Additionally, the authors examined all the patients’ personality profiles using a specific model that also other studies adopted: The psychobiological model [28, 38, 39, 47].

Personality traits are often studied in patients with rheumatic diseases and, most of all, in those with fibromyalgia. However, the literature on this topic presents inconsistent results. The proposed systematic review underlines some specific characteristics of the recent literature and highlights some relevant key-points for future researches. Firstly, there were many differences in the definitions of fibromyalgia and also in patient recruitment in the studies. Some authors only enrolled participants who were referenced in diagnosis, while some others used patients with a diagnosis formulated with ACR criteria of 1990 [17] and yet others with ACR criteria of 2010 [21].

Secondly, personality is studied under many aspects and a reference model is not always present. Many studies underline high levels of alexithymia and type D personality in FM patients but when depression is controlled, these results do not differ from those of healthy controls. Studies that use a comprehensive model of personality present a different theoretical approach and use alternatively the Big-Five model, Eysenck’s and Cloninger’s models. Obviously, when the theoretical model of personality changes, also the measures change, and that could explain the difference found between results. Therefore, the contrasting results are probably due to the use of different explicative models and diverse measures of personality. Malin and Little [40] observed that the scientific research examining personality characteristic in FM patients is limited by the differences in instrument design as well as by the limited data on clinical aspects of FM patients. They also did not find any study showing a specific personality profile in FM patients. In the study of Lundberg et al. [48] both aspects, such as temperament and character, of Cloninger’s TCI test were found different in FM personality.

In some cases, personality is studied in terms of psychopathology, with a completely different approach: Measures and results show how personality disorders can influence subthreshold dysfunctional traits. In these cases, personality is conceptualized as a feature, affecting patients’ quality of life and their response to treatment in general. Although in many studies FM patients are compared with healthy controls and personality differences are found, when comparison is made with other disorders with controlled depression, personality traits appear to be less relevant than before.

From this analysis, for future research, the relevance of a clear definition of fibromyalgia is evinced, together with the necessity to enrol participants on the basis of more recent criteria. Moreover, the use of a comprehensive model of personality and of psychopathological disorders, such as anxiety and depression, seems to be very relevant for a better understanding of a specific personality profile associated with fibromyalgia, also because of the high prevalence of Axis I psychopathologies in FM patients [45].

Obviously, some limits are present in our study: Our choice of scientific databases, such as PsycInfo and PubMed and the inclusion criteria (such as the English language), could exclude important studies in the field. Furthermore, most of the studies include female participants and thus no gender differences are controlled. For future research, it might be useful to extend the analysis of the literature on this topic, focusing on gender differences in personality aspects and their relationship with fibromyalgia.