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The paper by Viana et al1 analyses the relationship between Harlequin syndrome2 and headache. One facet of this interesting syndrome is the demonstration of pupillary signs by pharmacological studies explicable by the sudden onset of parasympathetic and sympathetic deficit, implicating an autonomic neuropathy mediated by an autoimmune process or viral infection.3
Sympathetic innervation of human cerebral and extracranial circulation is well documented. Parasympathetic innervation of cranial arteries has been established in rat, cat and monkey, but information on humans is meagre. Stimulation of the pre- or post-ganglionic fibres of the sphenopalatine ganglion in animals …
Competing interests None.
Provenance and peer review Commissioned; internally peer reviewed.