Abstract
Proposals for the diagnostic criteria for hemicrania continua (HC) and also for the nosological status of HC are set forth. The clinical constellation of symptoms and signs making up HC consists of: unilaterality without side shift; absolute indomethacin effect; and long-lasting repetitive attacks of varying duration, eventually with a chronic pattern, the pain being mild to severe. For the typical clinical picture of HC, including a positive ‘indotest’, we propose the term hemicrania continua vera. More or less analogous, but ‘indotest-negative’ clinical pictures have provisionally been termed hemicrania generis incerti (of undetermined nature). At the present level of knowledge, the diagnosis of hemicrania generis incerti should be made mostly by exclusion. HC may possibly best be classified along with chronic paroxysmal hemicrania (CPH) as this is the only other headache absolutely responsive to indomethacin. The bond between these two headaches on the one hand and cluster headache on the other should, at most, be a loose one. Interrelationships of these four classifiable headaches are briefly discussed.
Keywords
Introduction
In the present communication, diagnostic criteria for hemicrania continua (HC) are proposed. Since the positioning of this headache in the classification has not been determined so far, our points of view regarding the nosological positioning of HC are also set forth.
HC was described as a syndrome in 1984 (1). On a world-wide basis, the number of HC cases increased to 18 during the next 5 years (2), whereas during the first 6 years after the description of chronic paroxysmal hemicrania (CPH) (3) only eight cases of CPH had been diagnosed. Nevertheless, this relatively small number of cases reported in the literature at the time may have been one reason for not including HC in the International Headache Society (IHS) classification system in 1988 (4). More recently, a clinical description of HC has been included in the International Association for the Study of Pain (IASP) classification (1994) (5). Fifteen years after the first report, a number of patients have been detected around the world (6, 7). Single cases of typical HC are not systematically published anymore; the real number of diagnosed cases probably is considerably higher than summing-up figures from the literature would indicate.
This headache category is still sub judice. Hemicrania continua does not seem to be a sub-fraction of the so-called chronic daily headache, as claimed by others (8). The reason for this statement is twofold. First, the unilaterality, the absolute response to indomethacin, and the occasional autonomic phenomena, should rather link this disorder to CPH. Secondly, a daily occurrence should not be sufficient for including this headache in the same category as other conditions with a pathophysiology distinct from that of HC. Hemicrania continua should probably be included in IHS group 3.
The diagnostic criteria
The criteria are presented in Table 1.
Hemicrania continua: diagnostic criteria
∗The pain is mostly in the ‘anterior’ area, but not infrequently also in the auricular/occipital area.
†Provided the dosage is adequate: 150 mg per day for 3 days. In the doubtful case, the ‘indotest’ should be carried out (see Headache 1998; 38:122–128). This is particularly important in the remitting cases, since a betterment of pain in reality being due to a remission may falsely be ascribed to indomethacin.
‡There are two forms of HC from a temporal point of view: a remitting and non-remitting (chronic) form. There may be transitions from the one temporal pattern to the other. The continuous pattern may eventually seem to dominate.
§Lacrimation, conjunctival injection, rhinorrhea and nasal obstruction; such signs are usually meagre and on the symptomatic side, and, if present, they occur mostly during the more severe attack periods.
¶Nausea, vomiting, photo- and phonophobia, pulsatile character of pain and accentuation upon mild physical activity.
∗∗Reduction of range of motion in the neck; ipsilateral upper extremity discomfort; mechanical precipitation of pain/attacks.
The items under B (numbers I–IV) would seem to be more or less obligatory ones.
Item C I is non-obligatory; its presence nevertheless strengthens the diagnosis.
Each item under D (numbers I–IV) is non-obligatory, because of the ‘relative’ and not absolute character of each proviso. The reverse situation may present itself for each solitary negative proviso without violating the diagnosis (for instance autonomic features may be present, D I).
D III–IV possibly carry more weight than D I–II. If ‘cervicogenic’ symptoms and signs (D III) were present and marked, a diagnosis of HC alone would not necessarily be acceptable, even in the presence of an ample indomethacin-effect. Such cases should be reported separately to help upgrade future classification versions. D IV may possibly be an exception: one would hardly accept, for example, a complete triptan effect in HC.
A combination of the negative provisos may clearly favour a HC diagnosis.
Jabs or idiopathic stabbing headache are not mentioned among the criteria for HC. The reason for this is: although jabs appear not infrequently in HC, it is a highly unspecific phenomenon, appearing, for example, in migraine, tension-type headache, and also in headaches more similar to HC, such as cluster headache and CPH.
Classification
The possible link between HC and CPH
The nosological position of HC should reflect its clinical manifestations. HC belongs to the group of primary, strictly unilateral headaches. In addition, the striking response to indomethacin—a property common to HC and CPH—makes it reasonable to vent the idea of co-classifying HC with CPH. CPH is so far the only other headache absolutely responsive to indomethacin, a fact that, at this stage of insight, supposedly links such disorders. The strict unilaterality also strengthens the bond between them, and so does the clear female preponderance. It should be emphasized that both headaches also exhibit remitting and non-remitting clinical forms. The two headaches differ clearly as regards the following clinical variables: duration and degree of pain, and also the extent of autonomic involvement. Thorough search for additional, distinguishing traits between them has uncovered only minor—and mostly probably insignificant—differences (9).
Cluster headache and CPH
The similarity between HC and CPH by far exceeds that between CPH and cluster headache, where differences predominate (9, 10). The indomethacin response is a factor that crucially distinguishes cluster headache and CPH; the differing sex preponderance another; the prevalent temporal pattern a third; the lack of effect of ‘cluster headache drugs’ in CPH is a fourth, etc. Almost as important may be the abnormal sweating pattern demonstrated in the central part of the forehead on the symptomatic side in many cases of cluster headache, but not in CPH (11). These are actually decisive differences.
CPH was nevertheless provisionally categorized together with cluster headache (4). Whether this was a correct decision from a long-term perspective is open to debate. If this practice is going to be be continued, then a clear line, in our estimation, should be drawn between the two (9, 12). It is possible that 25 years after the description of CPH one may be facing an ‘inverse’ nosologic situation: that of unleashing the bonds to cluster headache. Clarity as to the relationship between cluster headache and CPH may also provide clarity as regards the nosological positioning of HC.
Hemicrania continua vera and Hemicrania generis incerti (of undetermined nature)
Just as in CPH, a positive indomethacin response is a fundamental property of HC. However, since the inception of HC, similar clinical pictures but unresponsive to indomethacin have been reported. It has been a matter of controversy whether such patients do suffer from an ‘indomethacin-resistant’ variety of HC, and the disagreement regarding this feature has been appreciable. Since no markers for HC are available, the actual relevant question is how HC may be diagnosed in the absence of an indomethacin effect. A hemicrania alone hardly suffices diagnostically. The nature of such a hemicrania with negative indomethacin response or where such response is untried remains most unclear; it may not belong to the HC cycle at all. Accordingly, we propose that the typical clinical picture of HC, including a positive ‘indotest’, be termed hemicrania continua vera. More or less analogous, but ‘indotest-negative’ clinical pictures can provisionally be termed hemicrania generis incerti (of undetermined nature).
The reponse to indomethacin was rather readily acknowledged as a diagnostic criterion of CPH. There has for instance been no temptation to consider cluster headache as an ‘indomethacin-resistant CPH’.
A proposal for classification of HC
A proposal for the classification of HC in context with cluster headache and CPH is set forth in Table 2. A heavy line is inserted between on the one hand cluster headache and on the other HC vera and CPH. In the future, it may even be preferable to classify the two indomethacin-responsive headaches separately from cluster headache as the few dissimilarities that may seem to exist between them may be just apparent. Actually, the bond between CPH/HC and cervicogenic headache may be stronger than the bond between CPH/HC and cluster headache.
Proposed classification of hemicrania continua and chronic paroxysmal hemicrania
A heavy line is inserted between cluster headache and the two indomethacin-responsive headaches to show the clear alienation between them.
∗The extent to which HC vera will persist in the remitting form is not entirely known.
†Provisional term. It could also probably be termed ‘hemicrania of undetermined nature’.
The advantages of provisionally considering HC vera and hemicrania generis incerti separately are obvious: (i) The clinicians will be less bothered by what are frequently experienced as cumbersome situations regarding response/non-response to indomethacin. (ii) The ‘indotest’ can be a useful procedure, enabling this clinical refinement. (iii) One can more conveniently share descriptions, also internationally, thus allowing further developments.
As far as diagnostic criteria of HC (vera) are concerned, one should mainly rely on the positive provisos. Negative provisos may minimize any possible uncertainty. Fulfilment of the criteria would more or less seem to ascertain a HC vera diagnosis. Until the nature of Hemicrania generis incerti is known, diagnosis should be made mostly by exclusion. This is a provisional diagnostic category, in all probability subject to repeated revisions. A constant critical eye on this subgroup may solve the present confusion and clarify whether this is a variant of HC vera or, what is more likely, whether it qualifies as one or more independent categories of headache. An unravelling of the pathogenesis may provide us with the final word.