Vertigo

It is the sensation of spinning or swaying while the body is actually stationary with respect to the surroundings. The effects of vertigo may be slight. It can cause nausea and vomiting and, in severe cases, it may give rise to difficulties with standing and walking.

The first task of the examining physician is to determine whether the vertigo is of central or peripheral origin.

The differentiation can be made at the bedside on the basis of

• the type of the spontaneous nystagmus
• head-thrust test
• the severity of imbalance
• the presence or absence of associated neurologic signs.

Type of Nystagmus
Nystagmus of peripheral origin is typically horizontal with a torsional ( rotational ) component. While those of central origin is often purely horizontal, vertical or torsional and usually changes direction with changes in the position of the gaze.

Severity of Imbalance
Patients with an acute peripheral vestibular lesion typically can stand, although they will veer toward the side of the lesion. By contrast, patients with vertigo of central origin are often unable to stand without support.

Head-Thrust Test
It is performed by grasping the patient's head and applying a brief, small amplitude, high acceleration head turn, first to one side and then to the other while the patient fixates on the examiner's nose.
If the catch-up saccades occur after the head thrusts in one direction but no after those in the other direction, this indicates the presence of a peripheral vestibular lesion on that side ( in the labyrinth or the 8th nerve including the root's entry zone in the brain stem )
Watch:
http://www.youtube.com/watch?v=j_R0LcPnZ_w&feature=related
http://www.youtube.com/watch?v=TqTtH1leYyk
A positive head thrust test can occur with brain stem infarction involving the entry zone of the root of the 8th nerve, but invariably, there will be other associated signs of the lateral brain stem (e.g., Horner's syndrome, facial numbness and weakness, hemiataxia and dysarthria )

Presence or Absence of associated neurologic sign
Associated neurological signs such as dysarthria, incoordination, numbness, or weakness suggest a central origin.