Cutaneous allodynia in transformed migraine patients

There is growing evidence that central sensitization plays a role in migraine pathogenesis, and that cutaneous allodynia is its clinical correlate. In headache research, allodynia has largely been studied in episodic migraine. The purpose of this investigation was to determine whether cutaneous allodynia occurs in transformed migraine, using individuals without headaches as controls.

Fifteen patients with a diagnosis of transformed migraine and 15 control subjects with no history of headaches were included. All subjects were females between 18 and 50. Similar to the methods of Burstein et al, Von Frey hairs (VFH) were sequentially applied to territories supplied by divisions of the trigeminal nerve, cervical paraspinal muscles, trapezius muscles, ventral forearm, and lower leg to determine a pain threshold. As a milder stimulus, a cotton swab was stroked in the same locations. Each trial was repeated 3 times on 2 occasions. Group comparisons were made using the Student's t-test.

Mean pain thresholds were lower among migraine patients than control subjects across all test areas. The thresholds were statistically significantly lower in migraine patients than in control subjects for the 1st division of the trigeminal nerve (34.0 g versus 115.8 g, P= .035) and for the 2nd division (23.5 g versus 97.6 g, P= .039). Six patients found a cotton swab-stroke painful, compared to zero control subjects. Using a quantitative definition of allodynia, 75% of patients had allodynia to mechanical stimuli.

This study is the first to demonstrate allodynia in transformed migraine patients using a headache-free control population and supports the hypothesis that central sensitization plays a role in the evolution of transformed migraine.