Symptoms and Causes of Chronic Subjective Dizziness

The term chronic subjective dizziness (CSD) is used to describe a commonly encountered type of dizziness that is not easily categorized into one of several other types, and for which the physical examination is typically normal.

Patients with CSD frequently initially suffer a sudden injury of some sort to their vestibular system, which is the neurologic network that preserves our sense of balance. Even after this initial injury has healed, people with CSD usually describe a vague sense of unsteadiness worsened by triggers in their environment. These triggers may include high places, standing on moving objects, or standing in motion-rich environments, like busy streets or crowds.

While formal diagnostic criteria for CSD are still being established, common symptoms include the following:

•  a sense of unsteadiness that is constantly present, though the severity may fluctuate
• disequilibrium is present for most days over at least a 3 month period
•  symptoms are most severe when walking or standing, and usually absent or very minor when laying still.
• symptoms are worsened by motion, exposure to moving visual stimuli, or performing precise visual activities.

The disorder usually comes on after an acute disorder that disrupts the vestibular system. Also, it occurs in the presence of acute or recurrent medical and/or psychiatric problems such as minor depression, anxiety, or obsessive/compulsive traits.

The exact cause of chronic subjective dizziness is still being worked out. The general theory, however, is that the disorder results from the brain’s inability to readjust after the vestibular system has been damaged.

The inner ears connect to the vestibulocochlear nerve, which sends signals to the vestibular nuclei in the brainstem. These nuclei work with other areas of the brain to integrate information about posture and motion with other sensory information such as vision. When the vestibular system says one thing, like “we’re moving,” and the other systems say, “no, we’re not,” dizziness is a common result.

The inner ears normally balance each other out. For example, if you turn your head to the right, one vestibulocochlear nerve is more active than the other, and the brain interprets the difference in signal power as a head turn. So what happens if the signal from one ear is dampened by something else, like an infection? The vestibular nuclei send information to the rest of the brain that the head is turning, even if in reality the person is standing still.

Brains are usually very adaptable and can learn to adjust to changes in neural signals. Just like your eyes adjust to being in a darker room or your ears get used to a constant background hum, the brain usually works around a vestibular deficit in order to establish a new working model of the world. After damage is done to the vestibular nerve, the imbalanced electrical signals are eventually understood to be the new normal, and life goes on.

In CSD, the brain fails to adjust to a new normal. Even though the original insult may have healed, the brain remains hyper-vigilant to anything that has to do with motion or balance, like a soldier who, home from war, still jumps or ducks for cover every time a car backfires.

In addition, underlying personality traits or psychiatric disorders may contribute to this inability to correctly estimate movement. Perhaps a shared underlying mechanism, such as a relative deficit in a particular neurotransmitter, causes both the personality trait and the sense of imbalance.

CSD is still gaining recognition within the medical community, and so the exact prevalence is uncertain. That said, in academic centers where the disorder is recognized, it's among the most common causes of dizziness in people who go to those centers. This means that other, better-recognized causes have usually been excluded by other doctors prior to making the referral.

If you haven’t already, talk to your doctor about the diagnosis. While not all physicians may recognize the disorder, most will be happy to look into it or at least make a referral. It's important you do speak with a medical professional, however, since there are treatments available for CSD.