What are the causes of vertigo?
While there are many causes of vertigo, the major distinction is between
central causes of vertigo and peripheral causes. Central causes occur because of
an abnormality in the cerebellum of the brain.
Distinguishing between central and peripheral causes for disease is an
important concept in evaluating neurologic problems. The brain and spinal cord
make up the central nervous system while the peripheral nervous system describes
the nerves outside the central area. Sometimes it is easy to make the
distinction, other times it is more difficult to distinguish between central and
peripheral causes. For example, if a person hits their funny bone (elbow) and
develops pain and numbness in their hand, it is mainly due to a direct blow to
the ulnar nerve at the elbow. This is a peripheral nerve problem and most people
would not seek medical care. If however, a person's leg became numb and weak,
the cause may be central (perhaps a stroke in the brain) or there may be a
peripheral cause (sciatica or nerve impingement).
Our orientation in space and, therefore, our balance or equilibrium, is
primarily measured by three sensory systems:
- The eye (visual) system
- The balance (vestibular) system of the inner ear
- The general sensory system including motion, pressure, and position
(proprioception) sensors in joints, muscles, and skin.
These three systems continuously feed information to the brainstem and brain
about our position in space relative to gravity and the world. The brainstem
connects the brain to the spinal cord. The brain, in turn, processes these data
and uses the information to make adjustments of our head, body, joints, and
eyes. When all three sensory systems and the brain are properly functioning, the
final result is a healthy balance system.
Visual input shows the brain where it is in space, what direction it is
facing, what direction it is moving, and whether it is turning or standing
still. Simple tasks like walking and picking up an object are much easier if we
can see our surroundings. Feeling seasick is a problem resulting from a
miscommunication between a healthy visual system and a healthy inner ear
(vestibular) system. In this circumstance, the ears are telling the brain that
there is movement, while the eyes may be seeing the fixed surroundings of the
cabin. Changes in visual acuity, glaucoma, and cataracts are examples of visual
problems that in some individuals may be enough to give them a balance disorder.
Vestibular system
The inner ear, or labyrinth, is located deep to the outer ear and middle ear,
and is encased within petrous portion of the temporal bone of the skull.
Figure 1. Diagram of outer, middle, and inner ear. The outer ear is labeled
in the figure and includes the ear canal. The middle ear includes the eardrum
(tympanic membrane) and three tiny bones for hearing. The bones are called the
hammer (malleus), anvil (incus), and stirrup (stapes) to reflect their shapes.
The middle ear connects to the back of the throat by the Eustachian tube. The
inner ear (labyrinth) contains the semicircular canals and vestibule for
balance, and the cochlea for hearing.
The vestibular structures of the inner ear are the vestibule (which is made
up of the utricle and saccule) and the three semicircular canals. These
structures work somewhat like a carpenter's level (a tool used to show how
"level" a horizontal or vertical surface is) or a gyroscope. Information is sent
by way of the vestibulocochlear nerve to the cerebellum of the brain, the part
that processes information regarding body balance and position. The rest of the
inner ear, the cochlea, is concerned with hearing.
The vestibular system measures linear and rotational movement. A number of
disorders can cause this system to stop working or provide inappropriate
information. These disorders include
Meniere's syndrome, labyrinthitis, benign
paroxysmal positional vertigo, ear infections, tumors, or trauma.
Peripheral sensory system
The sensory system consists of motion, position, and pressure sensors in the
skin, muscles, and joints. These sensors provide important touch and position
information to keep us balanced. For example, if someone pushes you from behind,
a slight increase will occur in the activity of the pressure sensors in the ball
of the feet. As these sensors note the increased pressure, the brain is
notified, and it knows from experience that the body is being pushed forward.
The brain then uses this information to tell the body to shift a small amount of
weight backward to prevent the body from toppling forward.
Brain
The brain processes the information from the three sensory systems. Any
problem that interferes with the proper functioning of the central nervous
system (CNS) can lead to a balance disorder. Unlike the problems associated with
the three sensory input systems discussed above, however, with CNS problems, it
is unusual to have vertigo as the only symptom. The most common causes of
vertigo are peripheral and involve the inner ear or labyrinth.
Some of the most common causes of vertigo are listed below:
- Benign paroxysmal positional vertigo (BPPV) may be caused when the crystals
in the inner ear become dislodged and irritate the semicircular canals. Often
the cause is not found but there may be an association with unusual positioning
or movement of the head. It is most frequently seen in people older than 60.
- Labyrinthitis may follow a viral infection which causes inflammation within
the middle ear.
- Meniere's disease is a group of symptoms associated with vertigo, hearing
loss and tinnitus or ringing in the ears.
- Acoustic neuroma is a benign tumor of the ear that can present with vertigo.
- Inner ear trauma may be due to a variety of mechanisms. A basilar skull
fracture may damage the labyrinth system directly or a
concussion, where that
area of the skull is shaken and may dislodge some of the inner ear crystals
causing symptoms of vertigo.
- The inner ear may also be affected by barotrauma, a condition where pressure
changes may be the causes of damage and vertigo. This type of injury is seen
when an individual dives into water and the air in the external ear canal is
compressed and damages the ear drum, middle, and inner ear. Barotrauma may also
occur as a consequence of diving where an increase of air pressure within the
middle and inner ear can cause structures to rupture. This may cause loss of
hearing if the tympanic membrane ruptures or it may cause vertigo if the round
and oval windows in the inner ear are damaged.
- Central causes of vertigo that arise in the brain are much less common.
Strokes, tumors,
seizures, and
multiple sclerosis may be associated with vertigo.
- Vestibular migraines describe
migraine headaches associated with vertigo and
are a common cause of balance disorders. Migraine is a blood vessel (vascular)
disease characterized by periodic, usually one-sided, headaches. These headaches
are often preceded for a variable time by associated neurological symptoms,
called the aura. Vertigo may occur in individuals with migraine as part of the
migraine aura or separately. In younger patients, the vertigo may predate the
onset of headaches entirely. A family history of migraine is very common and may
be a clue that a balance disorder may be migraine related.