Background
Migraine is experienced by the vast majority of sufferers as episodic migraine (EM) [
1,
2] occurring regularly although not necessarily frequently, with around 65% of sufferers estimated to have a migraine episode fortnightly to monthly [
3]. However if the episodic pattern becomes uncontrolled, a process of chronification occurs whereby the original episodic migraine becomes very frequent and more disabling. This is termed chronic migraine (CM) and is described by the International Headache Society (IHS) classifications [
4] as “
headache occurring on 15 or more days per month for more than three months, which, on at least 8 days per month, has the features of migraine headache”. On the days without migraine headache the individual can often suffer from pre and post headache effects adding to the burden of this condition.
The management of CM is more complex than EM, as it is often resistant to standard treatments with resultant additional costs compared to EM. The mean (SD) annual cost per CM person ($8243 [$10,646]) was over three times that of those with EM ($2649 [$4634]). Both direct medical costs and cost of lost productivity were substantially higher in CM than EM [
5]. In addition to financial costs, the social costs and personal impact of CM often leads to severe disability for those with CM [
6,
7]. This is especially true for females, with the annual prevalence of CM in women being 1.7–4.0% compared to men (0.6–0.7%) [
8‐
11]. Those women aged between 18 and 49 years of age are the most affected across the range of measures. In one study, CM sufferers were found to be three times more likely to have lost work and have reduced household productivity than those with EM (58% compared to 18%) [
12]. People with CM are also much more likely to report “very severe headache-related disability” as measured by the Migraine Disability Assessment Scale (MIDAS) than those with episodic (24.8 and 3.2% respectively) [
13,
14].
Despite the suggestion that migraine is a syndrome with multiple pathological mechanisms which support a multi therapeutic approach rather than a single approach [
15‐
17], the mainstay of treatment for CM is pharmacological. However, some patients do not want, or cannot, take some prophylactic medications such as Topiramate due to restrictions in its use [
18]. Currently, OnabotulinumtoxinA (Botox) is the only specifically licensed treatment for CM in the UK [
19]. Although its mechanism of action is unclear, studies have demonstrated that injecting specific sites on the head and neck produce significantly beneficial effects in CM patients. One study concluded that 32% of CM patients achieved a 50% reduction in headache days and a 50% reduction in migraine days, with NICE guidance recommending a 30% reduction in headache days as a measure of success in Botox studies [
20]. Although similar clinically significant reductions in the Headache Impact Test (HIT 6) scores are seen with Botox and Topiramate interventions, Botox has fewer side effects and higher adherence rates [
21,
22]. However, the efficacy of Botox in those patients who benefit only partially or not at all from Botox, and its relatively high cost, are barriers to an increased uptake [
23‐
25]. Therefore if adjunctive therapies, especially those with fewer side effects and relatively low costs could be utilised, this may increase the benefit to more of those with CM.
One possible adjunctive intervention is manual therapy. Despite the mechanisms of its potential action in CM being unknown, the basis for its potential role can be garnered from studies in associated conditions. These include primary headaches (tension type and migraine), as well as common comorbidities; chronic pain and specifically neck pain. One systematic review concluded that MT has an efficacy in the treatment of chronic tension headache equal to that of prophylactic medication with tricyclic antidepressant [
26]. Another involving massage therapy and chiropractic spinal manipulative therapy concluded that they may be as efficient as Propranolol and Topiramate in migraine prophylaxis. It also concluded that there is moderate quality evidence for both spinal manipulation and mobilisation as suitable treatments in chronic non-specific neck pain [
27]. These studies found benefits in at least one of the following: frequency, duration and intensity of headaches/pain.
Currently there are two theories in existence relevant to this study of manual therapy in the management of chronic migraine. One is that migraine is, in part, an abnormal response in those genetically pre-disposed, to nociceptive input involving the nerves of the upper cervical spine (C1, C2 and C3) and associated joints and muscles. This leads to exaggerated sensitisation of the trigeminal pathway and subsequent face, neck and head pain [
28‐
30].
The other theory incorporates the allostatic model in which people respond to stressful events, actual or perceived, with physiological and behavioural changes. In general these changes maintain normal physiological stability (allostasis). However, if stressors (including ongoing pain or nociceptive inputs) become too great or frequent then the normal response can become dysfunctional as a result of allostatic loading, which itself alters brain structure and function. Likewise, repeated migraines are themselves thought to be a driver of changes to the brain structure that may lead to a dysfunctional allostatic response. Consequently, many migraine sufferers report that stressful activities of daily living (physical and emotional) exacerbate their migraines [
31,
32].
Chronification from EM to CM may be a result of the stress mechanisms generating the migraine or as a consequence of changes in the brain arising in response to the attacks. Therefore if stressors (for example nociceptive pain, and central sensitisation, possibly from musculoskeletal disorders) can be reduced, this may add to the efficacy of existing interventions [
33].
Whilst the process of chronification in CM is not fully understood, there are a number of known associated risk factors including head and neck injury, and other pain disorders [
34] (Table
1).
Table 1
Risk factors associated with migraine chronification and reversion
• Obesity |
• Snoring |
• Sleep disorders |
• Excessive caffeine intake |
• Psychiatric/psychological disease (Depression/Anxiety) |
• High baseline headache frequency |
• Overuse of migraine abortive drugs |
• Major life changes |
• Head or neck injury |
• Cutaneous allodynia |
• Female sex |
• Comorbid pain disorders |
• Lower socioeconomic status |
Currently, one of the most common factors in chronification is considered to be the presence of medication over use headaches (MoH) due to the frequent use of opioids and barbituates in self medication of headaches, or in association with concomitant conditions. Estimates of between 30 and 72% of CM patients presenting at tertiary clinics are thought to have MoH associated chronification [
35,
36]. The IHS diagnosis of medication overuse is made if abortive drugs are used regularly for more than three months on 10 or more, or 15 or more, days a month, depending on the drug. One study estimated a twofold increase in chronification with opioid use on 8 days a month [
37]. Therefore any studies of interventions in CM should include a detoxification phase or a process to mitigate CM with MoH being included.
Both of the above migraine models suggest a role for altered sensory processing in the brainstem, which is associated with the presence of central sensitisation and one of the consequences, cutaneous allodynia (CA). Some studies cite CA as more prevalent in CM than EM, whilst others suggest there is little difference and it is more a reflection of migraine duration. There are a few potential reasons for these differences which include: the type of CA – thermal, dynamic and static mechanical; how it is measured and the temporal nature of CA making it difficult to measure consistently; and its role as a marker for the risk of frequent attacks rather than simply a consequence of frequent attacks [
38,
39]. CA is also consistently reported more in females than males (49.7% vs 32.6%%,
P < 0.001) [
40] and is common in other chronic pain conditions, with its presence associated with a reduction in the efficacy of abortive treatments [
41,
42].
Various models of MT and pain reduction exist which involve biomechanical, neurophysiological and psychological components, either individually or in combination. However all of these models consider that MT may work by activating descending inhibitory pathways via different levels of the spinal cord [
43‐
45]. The common relationship of central sensitisation, the cervical spine, and pain disorders (see Table
1) would suggest MT may have utility in the management of CM.
In terms of potential as an adjunctive treatment, MT has been shown to reduce pain and have a direct effect on the mechanics of the cervical spine that results in functional improvements [
46‐
48]. MT has also been shown to increase local pain pressure thresholds, which are used to detect central sensitisation [
49,
50]. Consequently, MT may reduce cutaneous allodynia and improve the efficacy of current approaches to treating CM.
The above discussion outlines commonalities between migraine, other pain conditions, its chronification and the potential for MT in its treatment. Combined with evidence showing the scope for improvement in existing CM treatment, this suggests there may be potential for the use of adjunctive non-pharmacological treatments, especially if these are generally associated with lesser side effects [
16,
51].
The objective of this study is to determine the effectiveness of MT as an adjunctive therapy to tertiary care (‘care as usual)’ in CM.