INTRODUCTION

The term "dizziness" encompasses a variety of sensations and can mean different things to different people. Generally, dizziness involves some disturbance in postural stability, locomotion, gaze stability or an illusion of motion. Patients will often describe the sensation more specifically as "spinning, unsteadiness, lightheadedness, dysequilibrium, disorientation, wooziness, floating, foggy headed or drunk feeling."

"Dizziness" can be the result of a disturbance in any part of the balance system, which includes integration and central processing of information received simultaneously from visual, vestibular and somatosensory inputs. The first step towards a diagnosis is categorizing the patient's complaints as consistent with central (brain), peripheral (ear), neither or both.

Balance disorders are a frequent problem, but more so in the elderly. Various studies indicate that "dizziness" is among the three most common complaints encountered in the primary care setting, sharing equal time with headaches and lower back pain.

The commonly used equation of dizziness equals inner ear disorder equals vestibular suppressant needs to be refigured. Currently 50% of patients seen in the primary care setting receive no diagnosis for their complaints of dizziness, yet 70% receive a prescription for Meclizine. Considering the known side effects, which include drowsiness, reduced reaction time and negative effect on the natural recovery process from vestibular injury, capricious or extended use of vestibular suppressant medication is frequently ineffective, and probably harmful.

The key to successful treatment is a specific and accurate diagnosis. Diagnostic techniques have improved dramatically and vestibular rehabilitation therapy has been proven effective.

STRUCTURE AND FUNCTION OF THE VESTIBULAR SYSTEM

As we move through our environment, information is gathered through our visual, somatosensory and vestibular senses, and sent to our brainstem for integration, then finally to our cortex for perception and processing. Our visual and somatosensory reference information is constantly changing as we move, but our vestibular reference - gravity - is unchanging.

The importance of the interaction between the peripheral vestibular apparatus, the brainstem and the other sensory receptors should not be understated.

The peripheral vestibular apparatus consists of matched pairs of sensors that are stimulated by any type of movement, with specific sensors responsible for specific movements. These sensors are known as the cupulas of the semi-circular canals and the otolith structures. The semi-circular canals are responsible for detecting angular head movement in the PITCH (shaking your head "yes") plane, the YAW (shaking your head "no") plane, and the ROLL (tilting your head to the side) plane. The arrangement of the semi-circular canals at right angles to each other causes the inner ear fluid (endolymph) to flow towards or away from the cupula with any of the above mentioned head movements. As long as the response registered in each of the matched canals on each side of the head is the same, balance is maintained. Benign Paroxysmal Positional Vertigo (BPPV), results from asymmetric response to head movement, due to an inappropriate response in one of the semi-circular canals to head movement stimulating fluid flow in the affected canal. The otolith structures are responsible for sensing translational movements in which the head is steady in relation to the body, but the body as a whole moves. The saccule registers vertical movements such as the sensation experienced when moving in an elevator. The utricle senses horizontal movements such as moving forward in a car.

The vestibular-ocular reflex (VOR) can be defined as reflexive eye movement in response to head movement. The role of the VOR is to allow for stable gaze or focus while the head is moving. It performs this function by causing eye movements that are equal and opposite of head movements; in effect, visually canceling out head movement.

It is impossible to voluntarily move the eyes at speeds needed to maintain visual acuity during typical head movements. The latency of response for the VOR is less than 16 milliseconds, while the latency for a voluntary eye movement is approximately 70 milliseconds. The VOR is compromised with damage to one or both peripheral vestibular apparatus'. Patients with chronic VOR deficit do not typically complain of vertigo, but rather complain of motion-provoked dysequilibrium or disorientation, as head movement results in a blurring of their visual environments.

SCREENING PATIENTS FOR APPROPRIATE REFERRAL

Since complaints of dizziness, vertigo or dysequilibrium can be the result of vestibular neurologic, vascular, psychologic and even spinal pathology, it is not always clear which specialty is appropriate for referral. In this age of cost awareness and effectiveness, the primary care physician must make important decisions as to the appropriateness and cost effectiveness of diagnostic procedures and referrals to specialists.

The goal of the initial office examination is to determine the probable site of lesion, peripheral versus central. A directed history and physical examination often allows for a more direct route to diagnosis and treatment.

A thorough history is critical for two main reasons:

• Patients have difficulty articulating their symptoms beyond simply describing themselves as "dizzy"
• Additional evaluation and treatment differ depending on the suspected site of lesion.

For most peripheral vestibular or "central" neurologic diseases, the eyes are the windows to the vestibular system. Inspection of eye movements can provide considerable information to assist in preliminary diagnosis. The two categories of eye movement are:

• The reflexive eye movements generated by stimulation of the peripheral vestibular apparatus.
• The voluntary eye movements generated in the cerebellum.

Certain patterns of nystagmus are associated with either peripheral or central site of lesion.

EVALUATION TECHNIQUES

The evaluation of the balance disordered patient has two specific goals:

• Locating the site of lesion
• Assessing the patient's functional ability

TREATMENT TECHNIQUES

The concept of treating vestibular patients with exercises rather than medicine has gained gradual acceptance since it was first introduced approximately 50 years ago. Observation of patients following vestibular injury revealed that those patients who were more active recovered faster and more completely than those patients who remained sedentary.

Treatment of balance disorders is determined by the specific type or location of pathology. These can be broken down into five general categories:

• Benign Paroxysmal Positional Vertigo (BPPV)
• Stable unilateral lesions
• Unstable unilateral lesions
• Bilateral stable lesions
• Non-vestibular balance disorders

Stable Unilateral Lesions The physiologic basis for recovery in this group is the recovery of the VOR through the plasticity of the vestibular system.

Unstable Unilateral Lesions The goal in treating these patients is to stabilize the response in the offending ear. Frequently, conservative measures such as diet, medications, and restorative surgery can stabilize the ear.

Bilateral Stable Lesions The goal of therapy is to train the patient in substitution strategies to improve gaze stability and postural stability. The patient is taught to maximize the use of visual and somatosensory information.

Non-Vestibular Disorders Examples of non-vestibular balance disorders would include patients with diabetic peripheral neuropathy or other neuromuscular conditions.

FALL PREVENTION

Falls are one of the most serious problems associated with aging. The statistics are startling. It is estimated that one-third to one-half of all people over the age of 65 fall at least once. In fact, falls are the leading cause of injury in older adults, and account for over 200,000 hip fractures annually in the United States alone. Of these, 25 percent will never regain full mobility. In essence, a fall leading to a hip fracture may forever change a patient's life.

The balance system involves many different parts of the body, all working in harmony with each other. Information is sent to the brain by your eyes, inner ears and proprioceptive system. (Proprioception is a term that describes our physical contact with the world, such as our feet on the floor, and hands on the steering wheel, etc.) Almost any move that you make will result in informaiton from all three inputs. If there is no conflict between the information received by the brain, you maintain your balance and go on your way.

An example of a conflict would be when a person is sitting in a car, stopped at a light, and a large truck next to the person moves suddenly. Frequently, one experiences a sensation of movement and finds oneself stepping on the brake and gripping the wheel. In this particular situation, the inner ear and proprioceptive information told the brain that there was no movement, but the visual information detected movement. The result is a temporary illusion of movement, or loss of balance.