- Email: [email protected]
Secondary headaches
Handbook of Clinical Neurology, Vol. 97 (3rd series) Headache G. Nappi and M.A. Moskowitz, Editors # 2011 Elsevier B.V. All rights reserved
Chapter 45
Secondary headaches: introduction GIUSEPPE NAPPI, 1 * AND MICHAEL A. MOSKOWITZ, 2 Chair of Neurology, “Sapienza” University of Rome and IRCSS “C. Mondino Institute of Neurology” Foundation, Pavia, Italy 2 Stroke and Neurovascular Regulation Laboratory, Departments of Radiology and Neurology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, USA
1
GENERAL DESCRIPTION
CLASSIFICATION
Secondary headaches, which are characterized by high epidemiological impact (Rasmussen and Olesen, 1992; Bigal et al., 2000), are certainly of multidisciplinary interest. Headache is sometimes the only sign of a severe underlying disease that must be identified as quickly as possible through a diagnostic process that can potentially involve any of the specialized medical or surgical fields, from general medicine to intensive care. In primary care settings secondary headaches account for around 44% of all headaches, and in 5% of cases they derive from neurological disorders (Bigal et al., 2000). Headache, presenting as an isolated or as an accompanying symptom, can signal the onset of a number of systemic and neurological diseases. Inflammatory, metabolic, and vascular causes, in that order of frequency, can cause the appearance of headache through mechanisms involving, respectively, the nerve endings of meningeal nociceptors, the neurotransmitter balance, and control of cerebrospinal fluid pressure. It follows that early detection and correct systemic contextualization of the symptom will yield the first information useful for interpreting the whole clinical picture.
Despite the considerable social impact of secondary headaches, the first systematic attempt to classify headache disorders (ICHD-I) was not published until as recently as 1988 (Headache Classification Subcommittee of the International Headache Society, 1988). The ICHD-I was structured as a single body, divided into 13 chapters, of which six (chapters 5–10) dealt with secondary headaches. The ICHD-II was published in 2004 following an extensive revision of the original classification which led to substantial changes being made to the main body of the work, to the general criteria, and to the disease-specific criteria. This new version is divided into three main parts: the primary headaches (chapters 1–4), the secondary headaches (chapters 5–12), and “cranial neuralgias, central and primary facial pain, other headaches” (chapter 13). The classification criteria are different for each of these parts, being, respectively, “symptom-based”, “etiological”, and “distribution-based”. The following definition of secondary headache is introduced: “a de novo headache occurring with another disorder recognized to be capable of causing it”, regardless of the phenomenological presentation. Basically, the ICHD-I and ICHD-II differ in structure and content as well as in the inclusion, in the updated version, of new topics.
STRUCTURE OF THE BOOK Basically, this book follows the nosological categories set out in the revised International Headache Classification (ICHD-II: Headache Classification Subcommittee of the International Headache Society, 2004). In some cases (diseases that generally imply a degree of urgency), in order to facilitate the diagnostic course after the initial assessment of the patient, the etiological classification criteria are integrated with “symptombased” algorithms.
ICHD-I VERSUS ICHD-II Headache is an extremely prevalent condition, which means that it can occur simultaneously with another disorder without a causal relationship. Therefore, a headache can only be diagnosed definitively as a secondary headache when an explicit cause-and-effect relationship has been established in scientific studies
*Correspondence to: Professor Giuseppe Nappi, Chair of Neurology, “Sapienza” University of Rome and IRCSS “C. Mondino Institute of Neurology” Foundation, Pavia, Italy, E-mail: [email protected]
498 G. NAPPI AND M.A. MOSKOWITZ between the underlying disorder and the headache. The in the case of “Headache attributed to infection”. In best way of establishing a causal relationship is to the first classification, this latter group was divided into document a close temporal association between the “intracranial” forms (listed in chapter 7: “Headache onset and disappearance of headache and of the causaassociated with non-vascular intracranial disorders”) tive disorder in large series of patients. Indeed, the and “systemic” forms (described in chapter 9: “Headauthors of the ICHD-II, as one of their main objecache associated with non-cephalic infection”). In the tives, set out to define as clearly as possible the revised classification, on the other hand, it is covered strength of the link between headache and the underlyin a single chapter (ICHD-II Chapter 9). Moreover, all ing disease. The two versions of the classification difthe paragraphs dealing with secondary headaches have fer from one another both structurally and in terms been considerably enriched with information regarding of content. In the ICHD-II the term “associated with”, both the characteristics of the pain and the salient feaused in the old version, has been replaced with the tures of the causative disease. This process of enrichstronger “attributed to”, to underline the link between ment has had some important therapeutic implications, the original cause and the headache. particularly in some sections, e.g., “Headache attributed The classification criteria are standardized, following to cranial or cervical vascular disorders”, in which many a fixed format based on four fundamental points. Point details have been added on the diagnosis of arteritis, A lists the salient features of the symptoms for descripand “Headache attributed to infection”, which has been tive purposes without making any mention of the possicompletely revised and updated. ble weight or hierarchy of these symptoms for that One new feature of the ICHD-II is the addition of particular headache type; point B establishes the presence an appendix in which the authors have included some of a new condition whose potential to induce headache recently reported variants of primary and, above all, has already been demonstrated; point C establishes the secondary headache forms for which there is still no presence of a temporal criterion linking the onset of definite evidence in the literature. the symptom (headache) with the underlying disease, Another new feature is the possibility of classifying while point D requires resolution of the headache within some conditions with more than one code. Patients prea variable period of time, depending on the partial or senting a pre-existing primary headache have to be complete resolution of the underlying disease. If this assigned two codes, the first indicating the previous, final criterion D is not met, then the relationship between primary headache diagnosis and the second the curcause and effect is classified as “probable”. rent, secondary headache diagnosis. The onset of a This format, which has made an important contribunew type of headache, potentially attributable to a tion to defining many forms of secondary headache, is new disease, can manifest itself in two ways: either also open to a number of criticisms. In some cases, the through a worsening of the pre-existing headache (in underlying disease can persist for a long time; this may this case the quality of the headache remains the be because of a poor response to treatment or because same), or through the onset of a new type of pain with of the intrinsic nature of the disease, as in the case of its own distinct characteristics. According to the some systemic infections. In these cases it can prove ICHD-II, both conditions can be classified as “secondimpossible, for a long time, to arrive at a nosological ary headaches”, providing the criteria establishing a categorization of the headache; this is why the term temporal link between the headache and the original “chronic post other disease headache” has been coined. cause, both during onset (criterion C) and resolution Some experts believe that these situations call for the (criterion D), are fulfilled. This new approach, entirely addition of a further criterion, E, which would rule different from that of the ICHD-I, reflects the authors’ out other diseases that can cause that same type of intention to found the classification of secondary headheadache. This would strengthen the pathogenetic link aches primarily on etiological criteria. between the headache and the underlying disease. A good example of this situation is that of the onset Compared with the previous classification, the of a daily headache theoretically due to an overuse of groups into which the secondary headaches were divided analgesics. In the first diagnostic phase this condition in the ICHD-II have been refined through the incorporacould be classified using three codes: primary headache tion of new elements to aid diagnosis. Some chapters (specific code), plus probable chronic headache (specihave been reorganized and renamed (“Headache attribufic code), plus probable medication overuse headache ted to head and neck trauma”, “Headache attributed (MOH, code: 8.2). Fulfilment of criterion D, which to cranial or cervical vascular disorders”, “Headache requires that the headache should resolve within attributed to disorders of homeostasis”), some are new 2 months of the discontinuation of the analgesics, chapters (“Headache attributed to psychiatric disorwould strongly support a diagnosis of MOH as ders”), and others have been considerably modified, as opposed to chronic headache.
SECONDARY HEADACHES: INTRODUCTION
COMMENTS AND PROPOSALS The lack of primary studies and the objective difficulty of planning such studies according to a correct and efficient methodology are, probably, the main limitations that, until the revision of the original international headache classification, prevented researchers from adopting a systematic approach to the secondary headaches. The authors of the new version of the classification (ICHD-II) have, with regard to the entire area of secondary headaches, sought, above all, to develop criteria that are both exhaustive but also readily useable for scientific and clinical purposes. This recourse to a standard format of diagnostic criteria for application in all the different categories of secondary headache, with the introduction of a few specific variants to cater for some pathologies, has simplified the physician’s task considerably and clarified our ideas with regard to this difficult and rather confused area. Although the results so far have been encouraging, we still encounter two main types of problem whose negative impact could be reduced considerably in the future: structural problems and problems related to the quality and quantity of ad hoc studies present in the literature.
Structural problems These are mainly linked to the use of a fixed format that is not always adaptable to specific situations. While, on the one hand, a precise and schematic approach is necessary, this can sometimes generate excessively “precise” assumptions, not always supported by literature evidence. Criterion D, in particular, states the period of time within which the headache must disappear once the causative disease has been resolved, but in many cases these estimates are not based on a careful review of the available literature data. On the basis of the same criterion, a secondary headache cannot be diagnosed until it is greatly improved or has disappeared, by which time the diagnosis is interesting only from the perspective of retrospective scientific studies. In many cases the patients have never fulfilled the criteria for a secondary headache, because they have never shown an improvement, but directly entered the chronic phase. As we have suggested, this problem could be resolved by the addition of a further criterion requiring the exclusion of other concomitant diseases that could, potentially, be responsible for the type of headache presented by the patient. This would, indirectly, strengthen the hypothesized link between the underlying disease and the headache. The “etiological” criterion, on which the whole section of the classification devoted to secondary headaches is supposed to be based, is not always respected.
499
This is seen most clearly in the chapter on “Headache attributed to infection” (Marchioni et al., 2006), where all the variants of lymphocytic meningoencephalitis share the same diagnostic code in spite of the fact that they are caused by different (viral, bacterial, fungal) etiological agents. The difficulties this creates are linked essentially to the considerable clinical, prognostic and therapeutic differences between these forms of meningoencephalitis, whose only common feature is the presence of lymphocytic pleocytosis in the cerebrospinal fluid. This problem could be resolved by a more rigorous etiology-based classification of these forms. Structurally, part 2 of the ICHD-II, which deals with secondary headaches, meets the needs of the researcher far more than those of the clinician. One solution might be to add to the current format a “symptom-based” classification that, especially in urgent situations, could help to guide the clinician when first faced with a patient affected by a secondary headache. The three main parts of the ICHD-II (primary headaches, secondary headaches, and cranial and facial pain) throw up some overlapping and not clearly classifiable situations. One typical example of this is TolosaHunt syndrome, which is classified in part 3 (code 13.17) but now recognized to be attributable to the presence of inflammatory granulomas in the orbit or in the cavernous sinus. Recent critical review has led to better definition of the characteristics of this condition, which should probably be included among the secondary headaches (La Mantia et al., 2006; Colnaghi et al., 2008).
Problems related to the quality and quantity of ad hoc studies present in the literature In fact, secondary headaches are the subject of very few, rather poor-quality studies. In many cases there are no targeted studies at all, or those that there are account for only a minimal percentage of literature reports pertaining to the topic in question. One effect of this lack of systematic studies is that it favors the employment of statements by “opinion leaders”. This is indeed why Olesen, in an editorial (2006), highlighted the need to submit some chapters of the classification to critical review, in order to bring out their shortcomings, and to plan primary studies targeting some specific secondary headache forms. In general, literature revisions are extremely time-consuming because they have to tackle the problem from every possible angle. But in this particular context they could be more structured and follow a simplified format aimed only at clarifying the critical points that
500
G. NAPPI AND M.A. MOSKOWITZ
constitute the core of the ICHD-II classification criteria: (1) the estimated prevalence of headache in the course of the underlying disease; (2) the features of the pain; and (3) the approximate mean times between appearance and resolution of the headache compared to the underlying disease. If parameters can be provided that reflect as closely as possible current knowledge on these three points the quality of the classification could be improved considerably.
REFERENCES Bigal ME, Bordini CA, Speciali JG (2000). Etiology and distribution of headaches in two Brazilian primary care units. Headache 40 (3):241–247. Colnaghi S, Versino M, Marchioni E et al. (2008). ICHD-II diagnostic criteria for Tolosa-Hunt syndrome in idiopathic inflammatory syndromes of the orbit and/or the cavernous sinus. Cephalalgia 28: 577–584.
Headache Classification Subcommittee of the International Headache Society (1988). Classification and diagnostic criteria for headache disorders, cranial neuralgias and facial pain. Cephalalgia (Suppl. 7):1–96. Headache Classification Subcommittee of the International Headache Society (2004). The international classification of headache disorders, 2nd edition. Cephalalgia 24 (Suppl. 1):9–160. La Mantia L, Curone M, Rapoport AM et al. (2006). Tolosa– Hunt syndrome: critical literature review based on IHS 2004 criteria. Cephalalgia 26 (7):772–781. Marchioni E, Tavazzi E, Bono G et al. (2006). Headache attributed to infection: observations on the IHS classification (ICHD-II). Cephalalgia 26 (12):1427–1433. Olesen J (2006). International classification of headache disorders, second edition (ICHD-2): current status and future revisions. Cephalalgia 26 (12):1409–1410. Rasmussen BK, Olesen J (1992). Symptomatic and nonsymptomatic headaches in a general population. Neurology 42 (6):1225–1231.
Chapter 45
Secondary headaches: introduction GIUSEPPE NAPPI, 1 * AND MICHAEL A. MOSKOWITZ, 2 Chair of Neurology, “Sapienza” University of Rome and IRCSS “C. Mondino Institute of Neurology” Foundation, Pavia, Italy 2 Stroke and Neurovascular Regulation Laboratory, Departments of Radiology and Neurology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, USA
1
GENERAL DESCRIPTION
CLASSIFICATION
Secondary headaches, which are characterized by high epidemiological impact (Rasmussen and Olesen, 1992; Bigal et al., 2000), are certainly of multidisciplinary interest. Headache is sometimes the only sign of a severe underlying disease that must be identified as quickly as possible through a diagnostic process that can potentially involve any of the specialized medical or surgical fields, from general medicine to intensive care. In primary care settings secondary headaches account for around 44% of all headaches, and in 5% of cases they derive from neurological disorders (Bigal et al., 2000). Headache, presenting as an isolated or as an accompanying symptom, can signal the onset of a number of systemic and neurological diseases. Inflammatory, metabolic, and vascular causes, in that order of frequency, can cause the appearance of headache through mechanisms involving, respectively, the nerve endings of meningeal nociceptors, the neurotransmitter balance, and control of cerebrospinal fluid pressure. It follows that early detection and correct systemic contextualization of the symptom will yield the first information useful for interpreting the whole clinical picture.
Despite the considerable social impact of secondary headaches, the first systematic attempt to classify headache disorders (ICHD-I) was not published until as recently as 1988 (Headache Classification Subcommittee of the International Headache Society, 1988). The ICHD-I was structured as a single body, divided into 13 chapters, of which six (chapters 5–10) dealt with secondary headaches. The ICHD-II was published in 2004 following an extensive revision of the original classification which led to substantial changes being made to the main body of the work, to the general criteria, and to the disease-specific criteria. This new version is divided into three main parts: the primary headaches (chapters 1–4), the secondary headaches (chapters 5–12), and “cranial neuralgias, central and primary facial pain, other headaches” (chapter 13). The classification criteria are different for each of these parts, being, respectively, “symptom-based”, “etiological”, and “distribution-based”. The following definition of secondary headache is introduced: “a de novo headache occurring with another disorder recognized to be capable of causing it”, regardless of the phenomenological presentation. Basically, the ICHD-I and ICHD-II differ in structure and content as well as in the inclusion, in the updated version, of new topics.
STRUCTURE OF THE BOOK Basically, this book follows the nosological categories set out in the revised International Headache Classification (ICHD-II: Headache Classification Subcommittee of the International Headache Society, 2004). In some cases (diseases that generally imply a degree of urgency), in order to facilitate the diagnostic course after the initial assessment of the patient, the etiological classification criteria are integrated with “symptombased” algorithms.
ICHD-I VERSUS ICHD-II Headache is an extremely prevalent condition, which means that it can occur simultaneously with another disorder without a causal relationship. Therefore, a headache can only be diagnosed definitively as a secondary headache when an explicit cause-and-effect relationship has been established in scientific studies
*Correspondence to: Professor Giuseppe Nappi, Chair of Neurology, “Sapienza” University of Rome and IRCSS “C. Mondino Institute of Neurology” Foundation, Pavia, Italy, E-mail: [email protected]
498 G. NAPPI AND M.A. MOSKOWITZ between the underlying disorder and the headache. The in the case of “Headache attributed to infection”. In best way of establishing a causal relationship is to the first classification, this latter group was divided into document a close temporal association between the “intracranial” forms (listed in chapter 7: “Headache onset and disappearance of headache and of the causaassociated with non-vascular intracranial disorders”) tive disorder in large series of patients. Indeed, the and “systemic” forms (described in chapter 9: “Headauthors of the ICHD-II, as one of their main objecache associated with non-cephalic infection”). In the tives, set out to define as clearly as possible the revised classification, on the other hand, it is covered strength of the link between headache and the underlyin a single chapter (ICHD-II Chapter 9). Moreover, all ing disease. The two versions of the classification difthe paragraphs dealing with secondary headaches have fer from one another both structurally and in terms been considerably enriched with information regarding of content. In the ICHD-II the term “associated with”, both the characteristics of the pain and the salient feaused in the old version, has been replaced with the tures of the causative disease. This process of enrichstronger “attributed to”, to underline the link between ment has had some important therapeutic implications, the original cause and the headache. particularly in some sections, e.g., “Headache attributed The classification criteria are standardized, following to cranial or cervical vascular disorders”, in which many a fixed format based on four fundamental points. Point details have been added on the diagnosis of arteritis, A lists the salient features of the symptoms for descripand “Headache attributed to infection”, which has been tive purposes without making any mention of the possicompletely revised and updated. ble weight or hierarchy of these symptoms for that One new feature of the ICHD-II is the addition of particular headache type; point B establishes the presence an appendix in which the authors have included some of a new condition whose potential to induce headache recently reported variants of primary and, above all, has already been demonstrated; point C establishes the secondary headache forms for which there is still no presence of a temporal criterion linking the onset of definite evidence in the literature. the symptom (headache) with the underlying disease, Another new feature is the possibility of classifying while point D requires resolution of the headache within some conditions with more than one code. Patients prea variable period of time, depending on the partial or senting a pre-existing primary headache have to be complete resolution of the underlying disease. If this assigned two codes, the first indicating the previous, final criterion D is not met, then the relationship between primary headache diagnosis and the second the curcause and effect is classified as “probable”. rent, secondary headache diagnosis. The onset of a This format, which has made an important contribunew type of headache, potentially attributable to a tion to defining many forms of secondary headache, is new disease, can manifest itself in two ways: either also open to a number of criticisms. In some cases, the through a worsening of the pre-existing headache (in underlying disease can persist for a long time; this may this case the quality of the headache remains the be because of a poor response to treatment or because same), or through the onset of a new type of pain with of the intrinsic nature of the disease, as in the case of its own distinct characteristics. According to the some systemic infections. In these cases it can prove ICHD-II, both conditions can be classified as “secondimpossible, for a long time, to arrive at a nosological ary headaches”, providing the criteria establishing a categorization of the headache; this is why the term temporal link between the headache and the original “chronic post other disease headache” has been coined. cause, both during onset (criterion C) and resolution Some experts believe that these situations call for the (criterion D), are fulfilled. This new approach, entirely addition of a further criterion, E, which would rule different from that of the ICHD-I, reflects the authors’ out other diseases that can cause that same type of intention to found the classification of secondary headheadache. This would strengthen the pathogenetic link aches primarily on etiological criteria. between the headache and the underlying disease. A good example of this situation is that of the onset Compared with the previous classification, the of a daily headache theoretically due to an overuse of groups into which the secondary headaches were divided analgesics. In the first diagnostic phase this condition in the ICHD-II have been refined through the incorporacould be classified using three codes: primary headache tion of new elements to aid diagnosis. Some chapters (specific code), plus probable chronic headache (specihave been reorganized and renamed (“Headache attribufic code), plus probable medication overuse headache ted to head and neck trauma”, “Headache attributed (MOH, code: 8.2). Fulfilment of criterion D, which to cranial or cervical vascular disorders”, “Headache requires that the headache should resolve within attributed to disorders of homeostasis”), some are new 2 months of the discontinuation of the analgesics, chapters (“Headache attributed to psychiatric disorwould strongly support a diagnosis of MOH as ders”), and others have been considerably modified, as opposed to chronic headache.
SECONDARY HEADACHES: INTRODUCTION
COMMENTS AND PROPOSALS The lack of primary studies and the objective difficulty of planning such studies according to a correct and efficient methodology are, probably, the main limitations that, until the revision of the original international headache classification, prevented researchers from adopting a systematic approach to the secondary headaches. The authors of the new version of the classification (ICHD-II) have, with regard to the entire area of secondary headaches, sought, above all, to develop criteria that are both exhaustive but also readily useable for scientific and clinical purposes. This recourse to a standard format of diagnostic criteria for application in all the different categories of secondary headache, with the introduction of a few specific variants to cater for some pathologies, has simplified the physician’s task considerably and clarified our ideas with regard to this difficult and rather confused area. Although the results so far have been encouraging, we still encounter two main types of problem whose negative impact could be reduced considerably in the future: structural problems and problems related to the quality and quantity of ad hoc studies present in the literature.
Structural problems These are mainly linked to the use of a fixed format that is not always adaptable to specific situations. While, on the one hand, a precise and schematic approach is necessary, this can sometimes generate excessively “precise” assumptions, not always supported by literature evidence. Criterion D, in particular, states the period of time within which the headache must disappear once the causative disease has been resolved, but in many cases these estimates are not based on a careful review of the available literature data. On the basis of the same criterion, a secondary headache cannot be diagnosed until it is greatly improved or has disappeared, by which time the diagnosis is interesting only from the perspective of retrospective scientific studies. In many cases the patients have never fulfilled the criteria for a secondary headache, because they have never shown an improvement, but directly entered the chronic phase. As we have suggested, this problem could be resolved by the addition of a further criterion requiring the exclusion of other concomitant diseases that could, potentially, be responsible for the type of headache presented by the patient. This would, indirectly, strengthen the hypothesized link between the underlying disease and the headache. The “etiological” criterion, on which the whole section of the classification devoted to secondary headaches is supposed to be based, is not always respected.
499
This is seen most clearly in the chapter on “Headache attributed to infection” (Marchioni et al., 2006), where all the variants of lymphocytic meningoencephalitis share the same diagnostic code in spite of the fact that they are caused by different (viral, bacterial, fungal) etiological agents. The difficulties this creates are linked essentially to the considerable clinical, prognostic and therapeutic differences between these forms of meningoencephalitis, whose only common feature is the presence of lymphocytic pleocytosis in the cerebrospinal fluid. This problem could be resolved by a more rigorous etiology-based classification of these forms. Structurally, part 2 of the ICHD-II, which deals with secondary headaches, meets the needs of the researcher far more than those of the clinician. One solution might be to add to the current format a “symptom-based” classification that, especially in urgent situations, could help to guide the clinician when first faced with a patient affected by a secondary headache. The three main parts of the ICHD-II (primary headaches, secondary headaches, and cranial and facial pain) throw up some overlapping and not clearly classifiable situations. One typical example of this is TolosaHunt syndrome, which is classified in part 3 (code 13.17) but now recognized to be attributable to the presence of inflammatory granulomas in the orbit or in the cavernous sinus. Recent critical review has led to better definition of the characteristics of this condition, which should probably be included among the secondary headaches (La Mantia et al., 2006; Colnaghi et al., 2008).
Problems related to the quality and quantity of ad hoc studies present in the literature In fact, secondary headaches are the subject of very few, rather poor-quality studies. In many cases there are no targeted studies at all, or those that there are account for only a minimal percentage of literature reports pertaining to the topic in question. One effect of this lack of systematic studies is that it favors the employment of statements by “opinion leaders”. This is indeed why Olesen, in an editorial (2006), highlighted the need to submit some chapters of the classification to critical review, in order to bring out their shortcomings, and to plan primary studies targeting some specific secondary headache forms. In general, literature revisions are extremely time-consuming because they have to tackle the problem from every possible angle. But in this particular context they could be more structured and follow a simplified format aimed only at clarifying the critical points that
500
G. NAPPI AND M.A. MOSKOWITZ
constitute the core of the ICHD-II classification criteria: (1) the estimated prevalence of headache in the course of the underlying disease; (2) the features of the pain; and (3) the approximate mean times between appearance and resolution of the headache compared to the underlying disease. If parameters can be provided that reflect as closely as possible current knowledge on these three points the quality of the classification could be improved considerably.
REFERENCES Bigal ME, Bordini CA, Speciali JG (2000). Etiology and distribution of headaches in two Brazilian primary care units. Headache 40 (3):241–247. Colnaghi S, Versino M, Marchioni E et al. (2008). ICHD-II diagnostic criteria for Tolosa-Hunt syndrome in idiopathic inflammatory syndromes of the orbit and/or the cavernous sinus. Cephalalgia 28: 577–584.
Headache Classification Subcommittee of the International Headache Society (1988). Classification and diagnostic criteria for headache disorders, cranial neuralgias and facial pain. Cephalalgia (Suppl. 7):1–96. Headache Classification Subcommittee of the International Headache Society (2004). The international classification of headache disorders, 2nd edition. Cephalalgia 24 (Suppl. 1):9–160. La Mantia L, Curone M, Rapoport AM et al. (2006). Tolosa– Hunt syndrome: critical literature review based on IHS 2004 criteria. Cephalalgia 26 (7):772–781. Marchioni E, Tavazzi E, Bono G et al. (2006). Headache attributed to infection: observations on the IHS classification (ICHD-II). Cephalalgia 26 (12):1427–1433. Olesen J (2006). International classification of headache disorders, second edition (ICHD-2): current status and future revisions. Cephalalgia 26 (12):1409–1410. Rasmussen BK, Olesen J (1992). Symptomatic and nonsymptomatic headaches in a general population. Neurology 42 (6):1225–1231.