This is often classified as an affection of a different order from the neuralgias, but there seem to be no real grounds for this distinction.
The superficial neuralgias themselves are probably not one, but a group of affections, with the common bond of severe and paroxysmal pain.
Neither is what is called migraine always one and the same disease.
Although in its most typical form it presents very striking characteristics, such as a marked preliminary stage, with peculiar visual and sensory auras, sometimes occupying one entire half of the body, a short and regular course and periodical return, deep-seated pain without tender points, and prominent unilateral vascular disorders, yet these symptoms shade off by imperceptible degrees into those of neuralgia of the fifth pair, or more often into one or another form of unilateral neuralgic headache which stands midway between the two.
The vascular phenomena of migraine are believed by various observers, as is well known, to constitute the primary and essential pathological feature of the disease, and to be the cause of the pain. But this is a pure hypothesis, and as a matter of fact the cases are abundant in which no greater vascular changes are present than in other neuralgias of equal severity.
Migraine seems to occupy an intermediate position between the grave neuroses, especially epilepsy, and the neuralgias of neurosal origin.
The symptomatology will be described at greater length below.
GENERAL ETIOLOGY.—The causes of neuralgia may be divided into predisposing and exciting causes.
The most important of the first group are—
1. Hereditary tendencies;