So-called "vascular headache of the migraine type": one or more nosological entities?

The dispute about whether migraine and cluster headache are one disorder--the "unified theory"--or two facets of a spectrum of "vascular headache" has not yet been settled. The author discusses various clinical features that unite or divide migraine and cluster headache in this respect: so-called "mixed forms" of vascular headache, corneal indentation pulse amplitudes, partial Horner's syndrome and possible aberrations in histamine metabolism. Evidence is presented showing that there may exist subunits of cluster headache, such as chronic paroxysmal hemicrania (C.P.H.) and a hitherto unreported type that co-exists with recurring bouts of retrobulbar neuritis and a partial factor XII deficiency.