Allodynia in cluster headache.

Cutaneous allodynia (CA), the perception of pain when a non-noxious stimulus is applied to normal skin, has been described in various pain syndromes. The pathophysiology of CA in headache is thought to be related to central sensitization of brainstem, and possibly thalamic, neurons. The recognition of CA in cluster headache (CH) is recent, and available data are scant. Some studies suggest the occurrence of CA in a significant proportion of CH patients. However, one study that examined sensory thresholds in CH failed to confirm this. CA in CH is characterized by rapid onset and termination, suggesting different mechanisms compared with CA in migraine. CA in CH is common in trigeminal areas but may spread to cervical dermatomes and beyond. The relations between the type of CH (episodic vs chronic) and CA are unknown. Further studies are needed to determine the mechanism of CA in CH, and its clinical implications.