DIFFERENTIAL DIAGNOSIS OF PERIPHERAL VESTIBULAR DISORDERS

Differential Diagnosis of Peripheral Vestibular Disorders

PART 1: Fluctuating Deficits

Unilateral fluctuating vestibular disease represents the most common clinical entity you will encounter among your dizzy patients. The most common diagnoses that are identified for unilateral fluctuating disease are benign paroxysmal positional vertigo (BPPV), Meniere’s disease (a.k.a. endolymphatic hydrops), and perilymphatic fistula (PLF) (Table I). Other disease processes that cause fluctuating vestibular input include autoimmune inner ear disease, superior semicircular canal dehiscence syndrome, ototoxicity, chronic suppurative otitis media/cholesteatoma, congenital inner ear malformations, syphilis, hypothyroidism, hyperlipidemia, and vascular loop compression syndrome. Other entities that less commonly cause fluctuating unilateral disease include disease processes that are traditionally considered to cause a fixed unilateral deficits. These include such entities as viral vestibular neuritis, labyrinthitis, vestibular schwannoma (acoustic neuroma), labyrinthine concussion, and after surgical disruption of the balance system on one side (e.g. after labyrinthectomy, vestibular nerve section, and acoustic tumor removal). The above list is not exhaustive…

After an insult of any kind to the inner ear the patient will immediately begin central compensation for the loss of vestibular function on that side. This can be noted clinically by the progression of a patient’s symptoms. Initially, a patient will have symptoms of whirling vertigo and nausea. After the spinning sensation resolves, there is a period where the patient notes a more subtle disequilibrium. This is generally described as lightheadedness and is most notable with quick head movements. Central compensation will gradually improve these symptoms if there are no further changes in the vestibular input from either ear. Eventually, in the great majority of patients, central compensation continues until the patient is essentially asymptomatic.

The duration to completion of compensation depends on the severity of the injury, medical condition and activity level of the individual patient. Central compensation can range anywhere from a few days to a year. In the case of fluctuating unilateral disease, the patient may not complete this process of central compensation before another insult to the vestibular system occurs. Consequently, patients with fluctuating unilateral disease will have the symptoms of the acute period (whirling vertigo) followed by days or weeks of the more subtle symptoms of dysequilibrium. The process then repeats itself with each insult to the inner ear. In summary, symptoms of unilateral fluctuating disease are characterized by whirling vertigo followed by variable periods of more subtle dysequilibrium.

Fixed Deficits

A fixed unilateral deficit is defined as any disease process that results in damage – partial or complete – to only one side of the peripheral vestibular system – the VIII^th cranial nerve or end organ. An additional requirement to this definition is that the damage is completed and the vestibular input from that side is no longer changing. So, a patient with active Meniere’s disease has a fluctuating unilateral disorder and a patient with inactive Meniere’s disease has a fixed unilateral deficit.

The multiple causes of fixed unilateral deficits can be discussed together not because they have similar symptoms at onset, but because they eventually wind up with the same collection of symptoms. These symptoms are derived from poor or inadequate central compensation to this unilateral vestibular injury. That said, most patients with fixed unilateral deficits are essentially asymptomatic or may have minimal symptoms, because most patients develop adequate compensation to these injuries.

Some of the most common causes of fixed unilateral vestibular deficits are vestibular neuritis, advanced (inactive) Meniere’s disease, trauma, post-surgical ablation of the vestibular system, ototoxicity and acoustic neuroma. Patients who have fixed unilateral deficits and have had poor compensation to these injuries will display generally similar symptoms. The most notable of these is disequilibrium with head movements – the faster the movement, the more notable the symptoms. This is particularly noted when the patient turns their head to the side of the injury.

Unlike the acute vestibular injury, these patients do not have severe episodes of whirling vertigo. Their symptoms may have a vertiginous component, but it is much milder and usually lasts only for a few moments. Another distinction from acute vestibular dysfunction or fluctuating unilateral disease is that fixed unilateral deficits generally do not produce symptoms (or symptoms can be alleviated) when the patient is motionless. In fluctuating disorders, the patient is often completely motionless during the worst part of their vertiginous spell.

Some symptoms of a fixed unilateral deficit:

Asymptomatic (most patients)
Chronic disequilibrium
Exacerbation with movement
No symptoms when motionless

One common fluctuating unilateral disorder that may be difficult to distinguish from a fixed unilateral deficit with poor compensation is benign paroxysmal positional vertigo (BPPV). This may be distinguished from a fixed unilateral deficit by an abnormal Dix-Hallpike test.

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