HPA Magazine 10
Dizziness is an incapacitating, non-specific and common symptom for many people. It can be defined as the illusion of movement and classified in four categories in accordance with the patient’s complaint: presyncope (nearly losing consciousness); loss of balance (sensation of unsteadiness); vertigo (illusion of movement, generally with a sense of spinning); and the sensation of “light-headedness” (unspecific form, without clear definition and diagnosis).
The most common type of dizziness is vertigo. In the majority of cases, patients describe a sensation where they or the objects around them are moving. It is the result of an injury or dysfunction in the labyrinth (structure of the inner ear), vestibular nerve or central structures of the vestibular system.
The labyrinth is made up of semi-circular canals and otolith organs that are responsible, for the sensation of angular movement and the sensation of linear movement, respectively. The central nervous system receives impulses from both of the labyrinths and compares them. The afferent discharges are exactly equated when the head is at rest. When moving, the impulses coming from the right and left labyrinths are aroused, then inhibited, generating differences in the activity of the eighth nerve, which are recognised as movement. The suppression of the left and right alternation is interpreted by the nervous system as vertigo and reflected as visual symptoms. The dysfunction of the semi-circular canals creates the sensation of spinning, while the dysfunction of the otolith system creates a sensation of floating or tilting.
The vestibular system makes connections with the cerebellum, the nuclei that control ocular motricity, the spinal cord and the cerebral cortex. The vestibular-ocular connections are responsible for the coordination of ocular movements when the head is moved, while the vestibulospinal tract helps maintain orthostatic posture. The cerebral connections modulate these activities.
The causes of vertigo are generically classified as central if the problem is in the central nervous system or peripheral if it is located in the structures of the inner ear or the vestibulocochlear nerve.
Peripheral causes are responsible for 80% of cases. These large groups present distinct signs and symptoms, however with some overlaps.
Vertigo is never a permanent and continuous symptom. Permanent injuries bring about adaptations of the central nervous system, and disappear within days or weeks. There can be a recurrence of the symptoms, triggered or exacerbated by movements of the head. Nausea and vomiting are the most common complaints in acute cases, mainly in vertigo of peripheral origin, but absent in mild cases and very short episodes.
Recurrent vertigo, lasting less than a minute, suggests benign paroxystic positional vertigo (BPPV). It is characterised by a single episode, lasting from just minutes to a few hours. Recurrent episodes lasting for hours suggest Menière’s Disease. Prolonged and serious episodes occur in vestibular neuritis, multiple sclerosis or cerebrovascular accident (stroke).
The history of traumatic brain injury (TBI), barotrauma and surgery of the middle ear should be investigated as a cause of perilymphatic fistula. A TBI can also be the cause of post-traumatic BPPV and of dissection of the vertebral artery with posterior fossa ischemia. Some medications can also cause dizziness or vertigo.
Ultimately, what causes the sensation of dizziness or vertigo is an injury to the structure or dysfunction of the vestibular labyrinth in the inner ear and/or of the pathways that connect it to the oculomotor system or the central nervous system.