Page 136 - The clinical aspects and management of chronic migraine Judith Anne Pijpers

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Chapter 7
risk for migraine chronification, and ultimately answer the question why some episodic migraine patients will develop to chronic migraine and others won’t. Due to the similarities of chronic migraine and other chronic pain conditions, some techniques used in the chronic pain field are interesting to apply in this setting. A technique used to quantify the trigeminal nerve in a non-invasive manner, is corneal confocal microscopy. The corneal nerve plexus is a densely innervated and highly dynamic plexus of small nerve fibers, mainly C-fibers, formed by the ophthalmic branch of the trigeminal nerve.38 Abnormalities in corneal nerve parameters haven been demonstrated in patients with peripheral (non-trigeminal) neuropathies, correlated to the severity of pain and used as a marker of dieseas.38,39 Corneal nerve fiber changes have also been suggested in a small study of chronic migraine patients.40 As the plexus is highly dynamic, the quantification by corneal confocal microscopy can be used for longitudinal measurements,41,42 even demonstrating posttreatment changes after 4 weeks.42 Another technique of interest is conditioned pain modulation, which assesses inhibition of pain by the descending pain pathway. Conditioned pain modulation tests comprise an isolated pain stimulus, and later on a second similar pain stimulus preceded by a conditioning stimulus, usually cold or hot water immersion. The read-out is the change in pain rating between the two pain stimuli. 43 Applying a conditioned stimulus has been shown to reduce migraine pain in episode migraine patients,44 suggesting a functional descending pain pathway.
A combination of these read-outs with Quantitative Sensory Testing to assess different types of allodynia (i.e. dynamic mechanical, static mechanical and thermal allodynia) and temporal summation (i.e. increment of pain at the end of a set of stimuli)27,45 would enhance interpretation of the involved mechanisms. As shown in chapter 6, an assessment of both a cephalic and extracephalic location is important.
Management of chronic migraine
Prevention of migraine chronification
Despite of the advancing insights in processes of central sensitization and lack of pain inhibition, direct intervention in these pathways in chronic migraine is not yet possible. With the role of CGRP in central sensitization, antibodies