"My doctor told me my crystals are out of place, and he said you could put 'em back. Have you ever heard of that?"
Many audiologists who perform vestibular testing hear some version of this question from their patients with benign paroxysmal positional vertigo (BPPV)—a common otologic cause of dizziness. BPPV is typically confirmed by performing the Dix-Hallpike maneuver and observing the client's eyes for nystagmus, a specific involuntary eye movement. Reports of the incidence of BPPV in patients with vertigo range from 20% to nearly 50% (Agrawal, Carey, Della Santina, Schubert, & Minor, 2009; Hanley, O'Dowd, & Considine, 2001; Neuhauser, 2007), although the true incidence of BPPV is difficult to estimate because many patients with the condition do not seek medical attention (Oghalai, Manolidis, Barth, Stewart, & Jenkins, 2000).
The body of evidence indicates that particle repositioning maneuvers—"putting the crystals back in place"—are effective in alleviating the signs and symptoms of BPPV, with reported overall success rates of 80%–95% (Blakely, 1994; Helminski, Zee, Janssen, & Hain, 2010; Hilton, Pinder, & Cochrane ENT Disorder Group, 2003).
Clinicians should take care in diagnosing BPPV. As this condition has achieved wider recognition in primary care and medical specialties, BPPV may be overdiagnosed in some of the millions of patients each year who seek medical attention for dizziness. The reason for this may be simple: Not all nystagmus seen in Dix-Hallpike testing is due to BPPV.
Identifying Spontaneous Nystagmus
In Barber and Stockwell's classic primer on electronystagmography (1977), spontaneous nystagmus is defined as present if it is persistent in three or more head positions, transient in four or more head positions, and of fairly consistent slow phase eye velocity greater than six degrees per second. It is advisable to record longer samples of eye movements—30 to 40 seconds—in patients reporting a history of acute onset of their symptoms, as this will improve identification of spontaneous nystagmus.
Spontaneous nystagmus can "beat" in horizontal, vertical, or (very rarely) torsional directions. The most common otologic causes of spontaneous nystagmus are vestibular neuritis—labyrinthitis accompanied by hearing loss—and Menière's disease. Nystagmus associated with these conditions is nearly always horizontal. In both pathologies, spontaneous nystagmus will be diminished or eliminated with visual fixation, and will follow Alexander's law—that slow phase velocity of nystagmus will increase upon gaze in the direction of nystagmus fast phase. Spontaneous nystagmus that lacks these features is more likely to denote a deficit of the central nervous system. The challenge for audiologists performing vestibular tests is that patients with vestibular neuritis or Menière's disease rarely are seen for evaluation during the acute stage of their disorder. Compensation or recovery mechanisms blunting spontaneous nystagmus may have begun by the time the patient is seen for testing.
That said, classic BPPV can develop following vestibular neuritis. Posterior semicircular canals—the locus of BPPV in most cases—are innervated by the inferior branch of the vestibular nerve, and Goebel, O'Mara, and Gianoli (2001) demonstrated that the superior branch appears to be more vulnerable to damage in vestibular neuritis. Consequently, patients with BPPV following vestibular neuritis also may have unilateral loss of horizontal semicircular canal function as a result of damage to the superior nerve—which would contribute additional symptoms. Testing for and treating only BPPV would be an unfortunate disservice to these patients.
Detecting Substance-Induced Nystagmus
A number of commonly used substances—including alcohol, some medications, and nicotine—can cause nystagmus that is not associated with BPPV.
Alcohol. Positional alcohol nystagmus is often mistaken for BPPV nystagmus, particularly in cases in which diagnoses are made, for example, in emergency departments in the middle of weekend nights. Although most pre-test instructions for vestibular testing include avoidance of alcohol, it is necessary to question patients carefully regarding alcohol consumption when low-velocity horizontal nystagmus is present in positional tests.
Medications. Many medications have an associated side effect of nystagmus. In particular, sedatives, anti-epileptic medications, and selective serotonin reuptake inhibitors are known to cause vertical nystagmus. Usually, this nystagmus is evident only in test conditions without visual fixation (e.g., positional tests), and is persistent, non-fatiguing, and not accompanied by subjective dizziness. It is not appropriate for an audiologist to direct a client to discontinue use of these medications prior to vestibular testing; however, carefully reviewing the patient's medication list when vertical nystagmus is observed during testing is warranted.
Nicotine. Nicotine use also can produce vertical nystagmus, which may be present for hours after the last use. You may not have much luck in getting nicotine users to avoid lighting up right before their vestibular test appointments, but recognizing nicotine-induced nystagmus will reduce the chance of misdiagnosing it as BPPV.
Testing Static Positions
When nystagmus is observed in positional tests, it is wise to go beyond the minimum required standard positions.
Chiari malformation. Kumar and colleagues (2002) report that 78% of their patients studied with Chiari malformation demonstrated abnormalities on vestibular testing, even if they were not symptomatic at the time of testing, and down-beating nystagmus was present in many of their patients. Other causes of down-beating nystagmus include episodic ataxia (type 2), paraneoplastic cerebellar degeneration syndrome, superior canal dehiscence, and migraine-associated vertigo. Nystagmus associated with these disorders may be present only in supine or prone static positional tests, and usually is immediate in onset, persistent, non-fatiguing, and not accompanied by dizziness.
Cervicogenic vertigo. Dizziness provoked by turning the head or flexing/extending the neck, regardless of the position of the head with respect to gravity, can result in nystagmus. Cervicogenic vertigo is seen in patients after head injury or whiplash, in patients with degenerative issues affecting cervical vertebrae, and in extreme athletic enthusiasts. Although diagnosis of cervicogenic vertigo can be elusive, horizontal nystagmus with dizziness upon turning the head to the extent of range of motion while sitting and supine certainly should raise suspicion of cervicogenic vertigo rather than BPPV.
Is It BPPV?
BPPV is by far the most common otologic cause of dizziness with nystagmus. Nystagmus provoked by movement or position of the head that is slightly delayed in onset, transient (decaying after a few seconds in the provoking position), fatigable (reduced with repeated positioning), and accompanied by vertigo is a hallmark of BPPV. Clinicians should watch for comments of "intractable BPPV" in the medical record, evidence of spontaneous nystagmus, and low-grade positional nystagmus that does not fit the "classic" pattern for BPPV—these could be warning signs that the client has some other condition.