Page 18 - The clinical aspects and management of chronic migraine Judith Anne Pijpers

Chapter 1
16
C: Sensitisation of the thalamus, causing cephalic and extracephalic allodynia
Recurrent stimulation by the trigeminal afferents, TNC of pain modulating pathways, induces sensitisation of the thalamus. Due to convergence of all sensory input of the skin, this causes extended cutaneous allodynia (extended cephalic and extracephalic allodynia)
DRG = dorsal root ganglia; TG = Trigeminal Ganglion; TNC = Trigeminal Nucleus Caudalis.
Image from Nervus Nascholing June 2017
Hence, cutaneous allodynia is a clinical marker of these central sensitisation processes. Cutaneous allodynia can be assessed in detail by elaborate sensory testing,15,21 but also by means of clinical information provided by patients with questions regarding hypersensitivity of head and extremities.22–24 Cutaneous allodynia symptoms appear to be more often present, and more severe in migraine patients with a high attack frequency as compared to a low attack frequency.23,25 Moreover cutaneous allodynia is an independent risk factor for migraine chronification.24 These findings signify the importance of central sensitisation in the process of migraine chronification.
Descending pain modulating pathways: lack of pain inhibition
The ascending nociceptive system described above (i.e. activation of the peripheral trigeminal afferents, signalling to the brainstem, thalamus and sensory cortex) is modulated by descending pain modulating pathways.This descending system can either facilitate or inhibit nociceptive transmission. Important structures of this system include the hypothalamus, the periaqueductal grey