Vertigo with upbeat nystagmus shortly after exposure to a small amount of organic solvent

Abstract Vertigo is a symptom with several possible etiologies. In this case, a 53-year-old woman presented with a 1-month history of vertigo. She had smelled an unpleasant organic solvent for three hours while working at a desk before the onset of vertigo. Physical examination revealed upbeat nystagmus and a wide-based gait but was otherwise unremarkable; no problems with coordination were observed. Further diagnostic tests, including MRI, inner ear function tests, blood sample analysis assessment of Vitamin B12 levels, and urinalysis, were performed. Vestibular rehabilitation and prevention of exposure to organic solvent were recommended to the patient. The upbeat nystagmus gradually subsided, then the nystagmus and gait disturbance resolved after six months. Patient history and past reports show that such a small amount of organic solvent can cause vertigo. This case highlights a diagnostic approach to vertigo and emphasizes the importance of obtaining a comprehensive history from the patient.


Introduction
Cases of vertigo caused by exposure to organic solvents have decreased recently because of countermeasures such as warnings against drug abuse and the establishment of strict work environment standards.Therefore, the possibility of examining patients is decreasing [1].Previous reports have attributed cases of organic solvent-induced vertigo to drug abuse, such as paint thinner inhalation, and the type of working environment, such as the painting industry [2][3][4][5].As reported in these studies, organic solvent-induced vertigo is related to a relatively high dose or long-term exposure to organic solvent.In this case, vertigo with upbeat spontaneous nystagmus may have been caused by short-term exposure to small amounts of organic solvents.Therefore, we report this phenomenon as a point of attention during history taking.

Case report
A 53-year-old woman was admitted to our otorhinolaryngology department with a primary complaint of persistent vertigo for one month.The patient experienced sudden onset vertigo after smelling an unpleasant odor.The vertigo was not paroxysmal but a persistent feeling of agitation.Physical examination revealed no abnormality except for upbeat nystagmus and wide-based gait.The upbeat nystagmus was spontaneous, not positional, and did not change with fixation.Blood sample examination, including Vitamin B12 assessment and brain MRI, revealed no abnormalities.Video oculography revealed upbeat spontaneous nystagmus.(Figure 1) Other tests to investigate inner ear function was normal.Video head impulse testing revealed normal vestibular-ocular reflex gain and no pathological saccade.Pure tone audiometry was in the normal range.Cervical and ocular vestibular-evoked myogenic potentials showed a symmetrical response.Distortion product otoacoustic emissions were present within normal limits.The patient reported that while working as a desk clerk in a building whose exterior was being painted, she came into contact with a paint thinner (a mixture of organic solvents such as toluene and xylene) for three hours.We suspected vertigo induced by organic solvent because of the trigger of the onset.Vestibular rehabilitation and prevention of exposure to organic solvent were recommended to the patient.Upbeat spontaneous nystagmus gradually subsided, and the spontaneous nystagmus and gait disturbance completely resolved after six months.The patient provided written informed consent for the publication of this case report.

Discussion
Historically, organic solvent-induced vertigo has occurred more frequently because of drug abuse (for example, paint thinner inhalation) and occupational exposure in the painting industry [2][3][4][5].However, in recent years, the number of related cases has decreased dramatically because of the establishment of countermeasures such as warnings against drug abuse and stricter work environment standards [1].A past report in 1985 showed that organic solvent-induced vertigo is often accompanied by centrally induced spontaneous nystagmus like vertical nystagmus [2].Vertical spontaneous nystagmus was reported in 60% of previous reports of vertigo caused by organic solvent poisoning, and centrally induced spontaneous nystagmus was associated in all 35 cases [4].Our theory that organic solvent poisoning caused the patient's clinical symptoms is consistent with concurrent vertigo and upbeat spontaneous nystagmus, particularly given the patient's history of exposure to organic solvents.This observation highlights a novel finding that vertigo can occur in response to even small amounts of organic solvent.The patient's exposure may be relatively low compared to previous reports of cerebellar damage (the velocity enhancement of the saccade) caused by short-term exposure to 120 ppm for 50 min [6] and the Japanese occupational environmental standard of 20 ppm for 8 h daily [7].This case shows that sensitivity to organic solvents varies among people and demonstrates the importance of asking patients with vertigo if they have been inadvertently exposed to organic solvents.
A previous epidemiological study reported that approximately 30% of vertigo cases were triggered by peripheral causes and 20% by central causes, while approximately 22% had an unknown cause [8].This study's findings show that the cause of vertigo is often unknown despite neuro-otological investigation.Many cases of vertigo also improve during the natural course of the disease: this may be one reason the condition has not been sufficiently investigated.Based on our experience, we believe it is important to actively question patients with unexplained vertigo about their exposure to organic solvents, including their occupational history.Although the symptoms of organic solvent poisoning, such as vertigo, may be irreversible [3], in this case, the patient showed improvement after six months of treatment, which may have been because of the low level of exposure.Therefore, patients with unexplained vertigo and a history of exposure to organic solvents should be advised to avoid such situations in the future to prevent exacerbation or recurrence of clinical symptoms and signs.

Conclusion
We present a case of vertigo that developed immediately after exposure to a small amount of organic solvents.Although organic solvent poisoning has become less common in recent years, we hope this case may be an opportunity to reaffirm that organic solvent can cause vertigo.The threshold may be lower than expected.In cases of vertigo of unknown cause, especially those associated with centrally induced vertical spontaneous nystagmus, it is important to inquire whether the patient has been exposed to organic solvents.If a history of exposure is suspected, it is beneficial to measure blood or urine levels of organic solvent as soon as possible.