Tuesday April 22 2008
Migraine affects one in 10 people
“Migraine hurts skin” is the headline in the Daily Mirror today. The newspaper describes the symptom of sensitive skin, called allodynia, where sufferers of migraine find combing their hair, wearing jewellery or getting dressed “excruciatingly painful”. The newspaper reports that 10% of people in the UK suffer migraine. The Daily Telegraph covers the same story and suggests “two thirds of migraine sufferers reported symptoms of the condition allodynia”.
The story is based on a questionnaire sent to 24,000 people living with different types of headaches. There is a chance the results are made less accurate by the number of people (over 30%) who did not respond to the questionnaire – only about 16,500 were returned fully completed. If these people had less severe symptoms and less skin sensitivity, the prevalence could have been reduced from two thirds to less than half. However, this still means that the symptom of sensitive skin is common among people who have migraines. The researchers are unable to say whether the presence of skin sensitivity is a risk factor for migraine progression. However, this could be a useful aspect for further study.
Where did the story come from?
Dr Marcelo Bigal from the Department of Neurology at the Albert Einstein College of Medicine in the Bronx and colleagues from elsewhere in the United States carried out this research. The study was sponsored by the National Headache Foundation and the lead researcher is now employed by Merck Research Laboratories. It was published in Neurology, a peer-reviewed medical journal.
What kind of scientific study was this?
This was a cross-sectional study in which the researchers used people who had been part of a previous large study and recorded as living with headaches. Using this group, they sent a random sample of 24,000 people a questionnaire which had 82 questions asking about headache diagnosis, other illnesses, and the impact that headache had on the patient’s life. They also asked background demographic questions, such as age, sex, race and income (which was classified in bands). This questionnaire had been validated in migraine sufferers.
Twelve of the questions specifically related to the frequency and severity of the symptom ‘cutaneous allodynia’. This symptom is described as a painful response to non-painful skin stimulation and is known to occur in migraine sufferers. The authors suggest that the presence of allodynia is suggestive of “central sensitisation”, a process where nerves in the central nervous system become involved in dealing with localised pain responses, meaning more pain sensations are transmitted.
The answers to the allodynia questions were scored as 0 (ie, never or rarely or does not apply to me), 1 (less than half the time) and 2 (half the time or more). This produced scores that ranged from 0 to 24 for the allodynia section. The researchers then summarised all the data descriptively and analysed the responses, looking for links between any of the responses and headache type, frequency, severity and other personal characteristics such as weight, that could determine the prevalence of allodynia scores of three or more.
What were the results of the study?
Of the 24,000 people sent the questionnaire, about 16,500 (69%) returned them completed. All of them had had at least one severe headache in the previous year and most (about 11,000) had a diagnosis of migraine. The researchers diagnosed other causes of headache from the questionnaires including probable migraine, chronic daily headache, severe episodic tension type headache and transformed migraine. The prevalence of allodynia was higher (68.3%) in those with transformed migraine (a form of migraine with very frequent attacks), than in the more common episodic form of migraine (63.2%). In both these types of migraine the prevalence of allodynia was higher than with the other causes of headache (around 36–42%).
When the researchers analysed the links between all the other personal characteristics, they found that the prevalence of allodynia in the migraine and transformed migraine groups was higher in women than in men and that it increased with disability score. Among the people with migraine, the symptom was also more common with more frequent headaches and higher body mass index. In all headache groups, the allodynia scores were higher in individuals with major depression.
What interpretations did the researchers draw from these results?
The researchers conclude that allodynia is more common and more severe in two types of migraine, transformed migraine and episodic migraine, than in other primary headaches. For those with migraine the chance of having allodynia is increased by being female, having frequent headaches, increased body mass index, disability and depression.
What does the NHS Knowledge Service make of this study?
This data, the researchers say, should be interpreted with caution:
- The use of a questionnaire that has been validated only in people with migraine for general use and in a population who have a wide variety of other headache types may have led to inaccuracies. For example, the questions about migraine symptoms may not have been understood by those people who did not have migraine.
- The classification of severity for the allodynia symptom was not the universally accepted ‘gold standard’ and although, the authors say, neither the gold standard nor their adopted scale are ideal, it will be difficult to convert the prevalence rates determined by their questionnaire into rates found in real life using conventional diagnosis.
- The cross-sectional study design means that it is not possible to determine if the symptom of allodynia predicts people who are more likely to develop more severe migraine over time, as the study was conducted at one point of time only.
A concern not mentioned by the researchers is the large number of uncompleted questionnaires (over 30%). This is not unusual in this type of study but in this case, it may mean that the prevalence of allodynia has been overestimated, as the non-responders may have had less severe or fewer symptoms of allodynia.
Despite these reservations, the study does provide evidence that this type of skin sensitivity is a common symptom occurring in migraine. Other studies following the development of the symptom over time and analysing the data in such a way as to allow patients and their doctors to predict either progression or responses to treatment, will no doubt be on the ‘to-do list’ for these researchers.