Relationship between fibromyalgia and temporomandibular disorders: A review of current understandings
http://www.100md.com
《中华医药杂志》英文版 2006年第3期
Correspondence to Daniele Manfredini,Viale XX Settembre 298,Marina di Carrara (MS),54036 Italy
Tel / Fax: +39-0585 630964,E-mail: daniele.manfredini@tin.it
[Abstract]The aim of this paper was to review hypotheses and current understandings about the fibromyalgia (FM) - temporomandibular disorders (TMD) clinical association, which represents a matter of arising interest. Findings from works addressing this issue suggested the existence of a certain degree of comorbidity between these two pathologies, which share many clinical features. Many FM patients present several symptoms and signs of stomatognathic involvement, with a TMD prevalence ranging from 42% to 97%; by contrast, a small amount of TMD subjects, up to 23.5%, receive a FM diagnosis as well.Hypotheses of association between TMD and FM have been discussed and, based on clinical and literature data, it seems plausible to draw some interesting considerations, which should be taken into account by clinicians for the management of orofacial pain.
[Key words]fibromyalgia;temporomandibular disorders;orofacial pain
BACKGROUND
In the complex field of temporomandibular disorders (TMD) etiology, many authors recognized the importance of some systemic diseases, such as rheumatic disorders [1, 2]. These pathologies are characterized by a multidistrictual involvement of connective, bony and muscular tissues and may affect musculoskeletal structures of the stomatognathic system as well, causing the onset of orofacial symptoms and signs [3].
Among these pathologies, attention has been mostly focused on the study of fibromyalgia (FM), a chronic non inflammatory rheumatism affecting soft tissues, whose main features are the presence of generalized musculoskeletal pain and tenderness to palpation. FM diagnosis is based on the American College of Rheumatology Criteria (ACR), requesting the presence of: 1) widespread pain in all four quadrants of the body for a minimum of three months and 2) at least 11 out of the 18 specific tender points [4].
Fibromyalgia is often accompanied by a constellation of symptoms like morning stiffness, fatigue, sleep disturbance, anxiety, headache, mood disorders and stress [5~7], which seem to be frequent in TMD patients, as well [8~12]. Moreover, many authors described a high prevalence of orofacial pain and mandibular dysfunction in course of FM [13~18] and others showed that patients with TMD can experience pain and tenderness outside the facial area [19~24]. Such investigations provided experience that fibromyalgia and temporomandibular disorders share several clinical features and suggested the existence of a link between these two diseases, so that the aim of this study is to review studies on this particular issue.
LITERATURE REVIEW
A work on a small sample of FM patients (n=8) showed that the degree of clinical mandibular dysfunction, according to the Helkimo index, was severe or moderate in all subjects, accompanied by severe anamnestic dysfunction in 75% of them [13].
Such preliminary observations inspired further researches and an increasing interest is growing up on the issue of TMD-FM comorbidity.
A study adopting standardized criteria for both TMD and FM diagnosis to facilitate cross-works comparison showed that most patients with fibromyalgia (75%) had myofascial face pain (MFP), as defined by the Research Diagnostic Criteria for Temporomandibular
Disorders (RDC/TMD). By contrast, only a small portion of MFP patients (18.4%) satisfied the ACR criteria for the diagnosis of FM. Moreover, levels of pain, fatigue, sleep disturbance and inability to work were higher in FM patients, so that the authors concluded that FM and MFP are two different clinical entities with a certain degree of reciprocal comorbidity [17, 25].
According to Hedenberg-Magnusson et al., other clinical parameters can differentiate these conditions, as for example pressure pain threshold and pressure pain tolerance level, presence of generalized joint/muscle pain and masticatory muscle tenderness. All these alterations were found to be more severe in FM patients [26].
Nevertheless, the observation that FM patients experience a more intensive orofacial symptomatology than TMD patients is not widely shared in the literature. For example, a comparative Italian study evidenced that patients with FM and MFP did not differ in temporomandibular joint (TMJ) pain and noises as well as in pain during mandibular function and muscle pain levels [27]. A similar investigation by Dao et al. found that the intensity of facial pain was similar between FM and MFP patients. Moreover, despite a high percentage (from 42.1% to 68.4%) of MFP subjects had experienced painful conditions outside the facial area, the authors claimed that MFP is unlikely to be a manifestation of a widespread body-pain condition, even though the possibility of a FM-TMD coexistence cannot be excluded. Findings from this paper also suggested that fibromyalgia should be considered in the differential diagnosis of myofascial face pain [8].
Another debated issue is the possible role of MFP as a first manifestation of some generalized painful musculoskeletal conditions.
In a work addressing this aspect, the prevalence and the onset of TMD were evaluated in subjects with FM (n=36),chronic fatigue syndrome (n=34) or both (n=22), showing that 42% of patients referred a prior diagnosis of TMD. This percentage is relatively low if compared with findings from other researches and could be explained by the study sample, partly consisted by chronic fatigue syndrome patients and by the anamnestic TMD diagnosis. However, most patients reported that the onset of orofacial pain was secondary to the widespread pain suggesting that facial pain should not be considered an early symptom of fibromyalgia [15].
Contrasting results were reported in a work by Raphael et al., who evaluated, by means of telephone interviews, some clinical parameters in 162 patients who had history of MFP. Thirty-eight patients (23.5%) reported a history of comorbid fibromyalgia and most of them referred that the onset of the facial and widespread pain occurred about in the same period. If they did not, the facial pain problem most often predated the widespread one. Moreover, the patients with both pathologies evidenced a higher intensity of pain during chewing and during mouth opening, a higher interference on social life and a more severe symptomatology, which conduced them to seek more medical treatments [28].
Another research assessed the prevalence of rheumatic diseases in a sample of 104 TMD patients, showing the presence of a rheumatic disorder in 56% of the subjects and fibromyalgia in 13% of them. Despite such degree of comorbidity, the authors excluded the causal role of rheumatic diseases for mandibular dysfunctions, claiming that this hypothesis could be satisfied only in the case of correspondence between the origin of the orofacial pain (muscles or joints) and the type of the rheumatism (muscular or articular one). Therefore, they concluded that rheumatic diseases can not be included among the main causal factors for TMD, even if they might worsen orofacial symptoms and signs and influence treatment response and outcome [29].
As regard the therapeutic approach to these pathologies, literature data seems to be concordant. For example, subjects affected by both diseases have less benefit by an occlusal splint treatment than patients with MFP alone [30]. Furthermore, recent preliminary data showed that FM patients with TMD symptoms and signs not responding to conservative TMD treatment may improve their symptomatology with a tactile stimulation therapy. The role of sleep as a factor arising serotonin levels is discussed in this paper as a reason for such improvement [31].
In general, observations from works on treatment efficacy suggest that facial pain sometimes can be an integral part of fibromyalgia symptoms, so receiving no benefits by conservative local TMD therapies and that fibromyalgia may represent a perpetuating factor for TMD symptoms.
In confirmation of this last consideration, results from a longitudinal prospective study on 600 TMD patients showed that FM has a significant effect on TMD pain progression at 36 months, so representing a risk factor for the progression to chronic orofacial pain [32].
Other researches hypothesized that the relationship between FM and chronic form of TMD should have its basis in some common epidemiological characteristics and in their comorbidity with headache, bowel complaints, stress, sleep and mood disorders [5, 11, 33]; besides, these two conditions may share peripheral and central mechanism of soft tissue pain as well [34].In conclusion, a consistent number of clinical reports confirmed the high prevalence of TMD among patients with fibromyalgia, ranging from 42% to 97% [13~18]; by contrast, the prevalence of FM in TMD patients seems to range from 4% to 23.5%[17, 28, 29, 35, 36].
DISCUSSION
The relationship between fibromyalgia and temporomandibular disorders gained much interest in the literature and several studies confirmed a certain degree of comorbidity between these two pathologies.The strong similitude of some clinical variables between FM and muscular TMD led to hypothesized some sort of relationship. For example, it was suggested that they might represent a different expression of the same condition[37]; they were considered as distinct disorders characterized by the same underlying pathophysiology[38]; MFP was suggested to be a regional expression of fibromyalgia[35] and it was also hypothesized that MFP and FM represent the extremities of a clinical continuum[39].
According to the present knowledge, fibromyalgia and myofascial face pain should be viewed as different pathologies for many reasons.
First, MFP affects a restrict group of muscles, with a regional localized pain characterized by the presence of trigger points (TrPs), while FM is a systemic disease characterized by widespread pain and the presence of tender points (TePs). Besides, myofascial pain typically arises as a response to an acute trauma or to a chronic overload while FM has an insidious onset with an unknown etiology; as a consequence, TrPs characterizing MFP gain benefit from local treatments while FM TePs request systemic treatments [27, 40, 41].
In view of such considerations, differences between the two pathologies seem to be striking, not justifying the current nosological confusion on this particular issue, which derives from problems inherent with their classification systems, both based on a combination of anamnestic and clinical criteria.
The anamnestic criterion requests the presence of muscular pain at different body-levels for the same period of time for both pathologies, while the clinical criterion requests tenderness to muscle palpation in both cases. The diagnosis of FM, according to the ACR criteria, is met if patients show tenderness in at least 11 out of 18 specified tender points [4]. An interesting observation is that masticatory muscles palpation is not provided among these 18 sites, so ACR criteria do not take in consideration the orofacial involvement, in course of FM syndrome. The clinical criterion for the diagnosis of MFP, according to the RDC/TMD, requests the presence of pain to digital palpation of at least 3 out of 20 muscle sites, all localized in the facial area [25].
Therefore, the Research Diagnostic Criteria for TMD, that currently represent the standard of reference for TMD diagnosis and classification in the research setting, do not provide a distinction between TrPs and TePs and may lead clinicians to make diagnosis of myofascial pain even in the absence of TrPs, which should represent its chief clinical parameter [42], and in the presence of TePs, which may be an expression of fibromyalgia syndrome.
Nevertheless, in a clinical setting clinicians should know the peculiar characteristics of TePs and TrPs [43, 44] for their correct evaluation, which is necessary to discriminate between localized and systemic muscular disorders.Most studies focused on the relationship between FM and muscular forms of TMD, and in particular MFP, for the above-mentioned reasons [8, 15, 17, 26~30, 33, 34] and only few researches considered the prevalence of the different forms of TMD in FM patients [13, 14, 16, 29, 36]. To our knowledge, only one study conducted such investigation using the RDC/TMD system. In that study it was shown that a high percentage of patients with fibromyalgia (86.7%) met criteria for at least one RDC/TMD diagnosis; in particular, the prevalence of myofascial pain (RDC/TMD Axis Ⅰ Group Ⅰ), disk displacement with reduction (RDC/TMD Axis Ⅰ Group Ⅱa), disk displacement without reduction (RDC/TMD Axis Ⅰ Group Ⅱb + Ⅱc) and arthralgia, osteoarthritis and osteoarthrosis (RDC/TMD Axis Ⅰ Group Ⅲ) was 76.7%, 43.3%, 13.3% and 63.4% respectively. By contrast only a small portion of TMD subjects (10%) resulted positive to ACR criteria for FM diagnosis.
Such results showed that many FM patients experience inflammatory-degenerative articular disorders, which could represent a secondary effect of the muscular suffering characterizing FM [45].
The presence of overlapping clinical features led some authors to classify fibromyalgia and temporomandibular disorders under the “Functional Somatic Syndromes”, a group of syndromes, among which the irritable bowel syndrome, the sick building syndrome and others, characterized by different somatic complaints which remain unexplained by identifiable disease even after extensive medical assessment. Such syndromes in many cases present a similar phenomenology, similar epidemiological characteristics and treatment outcome [46, 47]. Under this view, some works supposed that fibromyalgia and some orofacial chronic painful condition may share similar etiologic factors, among which stress has a primary role [8, 34]. An impairment in the normal activity of the hypothalamus-pituitary-adrenal (HPA) axis, that represents the main neuroendocrine pathway of the stress response, has been described in different papers dealing with FM and/or TMD, lending support to the hypothesis that psychoneuroimmunology may play an important role in chronic painful conditions [48~50].
However, etiopathogenetic mechanisms of FM and some chronic mandibular dysfunctions are far to be completely elucidated and further researches are needed on this particular issue.
CONCLUSIONS
Based on literature data, different considerations can be made about the FM-TMD clinical association.
Many patients with fibromyalgia, in a percentage ranging from 42% to 97%, report orofacial symptoms and signs, while only few subjects with TMD (4%~23.5%) are affected by FM. This last observation regards patients with muscular TMD in particular, and raised questions about the interpretation of myofascial face pain in those cases.
In general, there is agreement on the fact that fibromyalgia is a more severe and debilitating condition than temporomandibular disorders, even though some papers showed that FM and TMD patients experience an orofacial pain of a similar intensity, suggesting the need for a multidisciplinary approach in patients seeking treatment for stomatognathic symptoms and signs. Then, a careful evaluation of the orofacial pain should not leave a systemic examination of the patient out of consideration, as several researches demonstrated that facial pain may be an expression of some systemic diseases, as fibromyalgia, and a correct interpretation of tender and trigger points seems to be fundamental for the diagnosis of the nature of this pain.
The association between FM and TMD can be also casual, as they are common disorders in the clinical practice, and in such cases fibromyalgia may represent a worsening factor for TMD symptoms, influencing treatment response and outcome. Moreover, it can not be excluded that fibromyalgia may play a primary role in the onset of orofacial symptoms and signs in some cases.
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1 Department of Maxillofacial Surgery, University of Padova, Italy
2 Section of Prosthetic Dentistry, Department of Neuroscience, University of Pisa, Italy
(Editor Emilia)(Manfredini Daniele1, Salv)
Tel / Fax: +39-0585 630964,E-mail: daniele.manfredini@tin.it
[Abstract]The aim of this paper was to review hypotheses and current understandings about the fibromyalgia (FM) - temporomandibular disorders (TMD) clinical association, which represents a matter of arising interest. Findings from works addressing this issue suggested the existence of a certain degree of comorbidity between these two pathologies, which share many clinical features. Many FM patients present several symptoms and signs of stomatognathic involvement, with a TMD prevalence ranging from 42% to 97%; by contrast, a small amount of TMD subjects, up to 23.5%, receive a FM diagnosis as well.Hypotheses of association between TMD and FM have been discussed and, based on clinical and literature data, it seems plausible to draw some interesting considerations, which should be taken into account by clinicians for the management of orofacial pain.
[Key words]fibromyalgia;temporomandibular disorders;orofacial pain
BACKGROUND
In the complex field of temporomandibular disorders (TMD) etiology, many authors recognized the importance of some systemic diseases, such as rheumatic disorders [1, 2]. These pathologies are characterized by a multidistrictual involvement of connective, bony and muscular tissues and may affect musculoskeletal structures of the stomatognathic system as well, causing the onset of orofacial symptoms and signs [3].
Among these pathologies, attention has been mostly focused on the study of fibromyalgia (FM), a chronic non inflammatory rheumatism affecting soft tissues, whose main features are the presence of generalized musculoskeletal pain and tenderness to palpation. FM diagnosis is based on the American College of Rheumatology Criteria (ACR), requesting the presence of: 1) widespread pain in all four quadrants of the body for a minimum of three months and 2) at least 11 out of the 18 specific tender points [4].
Fibromyalgia is often accompanied by a constellation of symptoms like morning stiffness, fatigue, sleep disturbance, anxiety, headache, mood disorders and stress [5~7], which seem to be frequent in TMD patients, as well [8~12]. Moreover, many authors described a high prevalence of orofacial pain and mandibular dysfunction in course of FM [13~18] and others showed that patients with TMD can experience pain and tenderness outside the facial area [19~24]. Such investigations provided experience that fibromyalgia and temporomandibular disorders share several clinical features and suggested the existence of a link between these two diseases, so that the aim of this study is to review studies on this particular issue.
LITERATURE REVIEW
A work on a small sample of FM patients (n=8) showed that the degree of clinical mandibular dysfunction, according to the Helkimo index, was severe or moderate in all subjects, accompanied by severe anamnestic dysfunction in 75% of them [13].
Such preliminary observations inspired further researches and an increasing interest is growing up on the issue of TMD-FM comorbidity.
A study adopting standardized criteria for both TMD and FM diagnosis to facilitate cross-works comparison showed that most patients with fibromyalgia (75%) had myofascial face pain (MFP), as defined by the Research Diagnostic Criteria for Temporomandibular
Disorders (RDC/TMD). By contrast, only a small portion of MFP patients (18.4%) satisfied the ACR criteria for the diagnosis of FM. Moreover, levels of pain, fatigue, sleep disturbance and inability to work were higher in FM patients, so that the authors concluded that FM and MFP are two different clinical entities with a certain degree of reciprocal comorbidity [17, 25].
According to Hedenberg-Magnusson et al., other clinical parameters can differentiate these conditions, as for example pressure pain threshold and pressure pain tolerance level, presence of generalized joint/muscle pain and masticatory muscle tenderness. All these alterations were found to be more severe in FM patients [26].
Nevertheless, the observation that FM patients experience a more intensive orofacial symptomatology than TMD patients is not widely shared in the literature. For example, a comparative Italian study evidenced that patients with FM and MFP did not differ in temporomandibular joint (TMJ) pain and noises as well as in pain during mandibular function and muscle pain levels [27]. A similar investigation by Dao et al. found that the intensity of facial pain was similar between FM and MFP patients. Moreover, despite a high percentage (from 42.1% to 68.4%) of MFP subjects had experienced painful conditions outside the facial area, the authors claimed that MFP is unlikely to be a manifestation of a widespread body-pain condition, even though the possibility of a FM-TMD coexistence cannot be excluded. Findings from this paper also suggested that fibromyalgia should be considered in the differential diagnosis of myofascial face pain [8].
Another debated issue is the possible role of MFP as a first manifestation of some generalized painful musculoskeletal conditions.
In a work addressing this aspect, the prevalence and the onset of TMD were evaluated in subjects with FM (n=36),chronic fatigue syndrome (n=34) or both (n=22), showing that 42% of patients referred a prior diagnosis of TMD. This percentage is relatively low if compared with findings from other researches and could be explained by the study sample, partly consisted by chronic fatigue syndrome patients and by the anamnestic TMD diagnosis. However, most patients reported that the onset of orofacial pain was secondary to the widespread pain suggesting that facial pain should not be considered an early symptom of fibromyalgia [15].
Contrasting results were reported in a work by Raphael et al., who evaluated, by means of telephone interviews, some clinical parameters in 162 patients who had history of MFP. Thirty-eight patients (23.5%) reported a history of comorbid fibromyalgia and most of them referred that the onset of the facial and widespread pain occurred about in the same period. If they did not, the facial pain problem most often predated the widespread one. Moreover, the patients with both pathologies evidenced a higher intensity of pain during chewing and during mouth opening, a higher interference on social life and a more severe symptomatology, which conduced them to seek more medical treatments [28].
Another research assessed the prevalence of rheumatic diseases in a sample of 104 TMD patients, showing the presence of a rheumatic disorder in 56% of the subjects and fibromyalgia in 13% of them. Despite such degree of comorbidity, the authors excluded the causal role of rheumatic diseases for mandibular dysfunctions, claiming that this hypothesis could be satisfied only in the case of correspondence between the origin of the orofacial pain (muscles or joints) and the type of the rheumatism (muscular or articular one). Therefore, they concluded that rheumatic diseases can not be included among the main causal factors for TMD, even if they might worsen orofacial symptoms and signs and influence treatment response and outcome [29].
As regard the therapeutic approach to these pathologies, literature data seems to be concordant. For example, subjects affected by both diseases have less benefit by an occlusal splint treatment than patients with MFP alone [30]. Furthermore, recent preliminary data showed that FM patients with TMD symptoms and signs not responding to conservative TMD treatment may improve their symptomatology with a tactile stimulation therapy. The role of sleep as a factor arising serotonin levels is discussed in this paper as a reason for such improvement [31].
In general, observations from works on treatment efficacy suggest that facial pain sometimes can be an integral part of fibromyalgia symptoms, so receiving no benefits by conservative local TMD therapies and that fibromyalgia may represent a perpetuating factor for TMD symptoms.
In confirmation of this last consideration, results from a longitudinal prospective study on 600 TMD patients showed that FM has a significant effect on TMD pain progression at 36 months, so representing a risk factor for the progression to chronic orofacial pain [32].
Other researches hypothesized that the relationship between FM and chronic form of TMD should have its basis in some common epidemiological characteristics and in their comorbidity with headache, bowel complaints, stress, sleep and mood disorders [5, 11, 33]; besides, these two conditions may share peripheral and central mechanism of soft tissue pain as well [34].In conclusion, a consistent number of clinical reports confirmed the high prevalence of TMD among patients with fibromyalgia, ranging from 42% to 97% [13~18]; by contrast, the prevalence of FM in TMD patients seems to range from 4% to 23.5%[17, 28, 29, 35, 36].
DISCUSSION
The relationship between fibromyalgia and temporomandibular disorders gained much interest in the literature and several studies confirmed a certain degree of comorbidity between these two pathologies.The strong similitude of some clinical variables between FM and muscular TMD led to hypothesized some sort of relationship. For example, it was suggested that they might represent a different expression of the same condition[37]; they were considered as distinct disorders characterized by the same underlying pathophysiology[38]; MFP was suggested to be a regional expression of fibromyalgia[35] and it was also hypothesized that MFP and FM represent the extremities of a clinical continuum[39].
According to the present knowledge, fibromyalgia and myofascial face pain should be viewed as different pathologies for many reasons.
First, MFP affects a restrict group of muscles, with a regional localized pain characterized by the presence of trigger points (TrPs), while FM is a systemic disease characterized by widespread pain and the presence of tender points (TePs). Besides, myofascial pain typically arises as a response to an acute trauma or to a chronic overload while FM has an insidious onset with an unknown etiology; as a consequence, TrPs characterizing MFP gain benefit from local treatments while FM TePs request systemic treatments [27, 40, 41].
In view of such considerations, differences between the two pathologies seem to be striking, not justifying the current nosological confusion on this particular issue, which derives from problems inherent with their classification systems, both based on a combination of anamnestic and clinical criteria.
The anamnestic criterion requests the presence of muscular pain at different body-levels for the same period of time for both pathologies, while the clinical criterion requests tenderness to muscle palpation in both cases. The diagnosis of FM, according to the ACR criteria, is met if patients show tenderness in at least 11 out of 18 specified tender points [4]. An interesting observation is that masticatory muscles palpation is not provided among these 18 sites, so ACR criteria do not take in consideration the orofacial involvement, in course of FM syndrome. The clinical criterion for the diagnosis of MFP, according to the RDC/TMD, requests the presence of pain to digital palpation of at least 3 out of 20 muscle sites, all localized in the facial area [25].
Therefore, the Research Diagnostic Criteria for TMD, that currently represent the standard of reference for TMD diagnosis and classification in the research setting, do not provide a distinction between TrPs and TePs and may lead clinicians to make diagnosis of myofascial pain even in the absence of TrPs, which should represent its chief clinical parameter [42], and in the presence of TePs, which may be an expression of fibromyalgia syndrome.
Nevertheless, in a clinical setting clinicians should know the peculiar characteristics of TePs and TrPs [43, 44] for their correct evaluation, which is necessary to discriminate between localized and systemic muscular disorders.Most studies focused on the relationship between FM and muscular forms of TMD, and in particular MFP, for the above-mentioned reasons [8, 15, 17, 26~30, 33, 34] and only few researches considered the prevalence of the different forms of TMD in FM patients [13, 14, 16, 29, 36]. To our knowledge, only one study conducted such investigation using the RDC/TMD system. In that study it was shown that a high percentage of patients with fibromyalgia (86.7%) met criteria for at least one RDC/TMD diagnosis; in particular, the prevalence of myofascial pain (RDC/TMD Axis Ⅰ Group Ⅰ), disk displacement with reduction (RDC/TMD Axis Ⅰ Group Ⅱa), disk displacement without reduction (RDC/TMD Axis Ⅰ Group Ⅱb + Ⅱc) and arthralgia, osteoarthritis and osteoarthrosis (RDC/TMD Axis Ⅰ Group Ⅲ) was 76.7%, 43.3%, 13.3% and 63.4% respectively. By contrast only a small portion of TMD subjects (10%) resulted positive to ACR criteria for FM diagnosis.
Such results showed that many FM patients experience inflammatory-degenerative articular disorders, which could represent a secondary effect of the muscular suffering characterizing FM [45].
The presence of overlapping clinical features led some authors to classify fibromyalgia and temporomandibular disorders under the “Functional Somatic Syndromes”, a group of syndromes, among which the irritable bowel syndrome, the sick building syndrome and others, characterized by different somatic complaints which remain unexplained by identifiable disease even after extensive medical assessment. Such syndromes in many cases present a similar phenomenology, similar epidemiological characteristics and treatment outcome [46, 47]. Under this view, some works supposed that fibromyalgia and some orofacial chronic painful condition may share similar etiologic factors, among which stress has a primary role [8, 34]. An impairment in the normal activity of the hypothalamus-pituitary-adrenal (HPA) axis, that represents the main neuroendocrine pathway of the stress response, has been described in different papers dealing with FM and/or TMD, lending support to the hypothesis that psychoneuroimmunology may play an important role in chronic painful conditions [48~50].
However, etiopathogenetic mechanisms of FM and some chronic mandibular dysfunctions are far to be completely elucidated and further researches are needed on this particular issue.
CONCLUSIONS
Based on literature data, different considerations can be made about the FM-TMD clinical association.
Many patients with fibromyalgia, in a percentage ranging from 42% to 97%, report orofacial symptoms and signs, while only few subjects with TMD (4%~23.5%) are affected by FM. This last observation regards patients with muscular TMD in particular, and raised questions about the interpretation of myofascial face pain in those cases.
In general, there is agreement on the fact that fibromyalgia is a more severe and debilitating condition than temporomandibular disorders, even though some papers showed that FM and TMD patients experience an orofacial pain of a similar intensity, suggesting the need for a multidisciplinary approach in patients seeking treatment for stomatognathic symptoms and signs. Then, a careful evaluation of the orofacial pain should not leave a systemic examination of the patient out of consideration, as several researches demonstrated that facial pain may be an expression of some systemic diseases, as fibromyalgia, and a correct interpretation of tender and trigger points seems to be fundamental for the diagnosis of the nature of this pain.
The association between FM and TMD can be also casual, as they are common disorders in the clinical practice, and in such cases fibromyalgia may represent a worsening factor for TMD symptoms, influencing treatment response and outcome. Moreover, it can not be excluded that fibromyalgia may play a primary role in the onset of orofacial symptoms and signs in some cases.
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1 Department of Maxillofacial Surgery, University of Padova, Italy
2 Section of Prosthetic Dentistry, Department of Neuroscience, University of Pisa, Italy
(Editor Emilia)(Manfredini Daniele1, Salv)