Light cupula of the horizontal semicircular canal occurring alternately on both sides: a case report

A previously healthy 38-year-old man who suddenly developed positional vertigo was referred to our hospital. He reported that he woke up early in the morning because he felt severe vertigo. Vertigo symptom persisted even when the patient’s head was kept still, which was aggravated with a position change. He did not complain of audiological symptoms or headaches, and reported no previous history of vertigo or neurological disorders including migraine. The otoscopic examination revealed a normal tympanic membrane. Further examination yielded a very weak left-beating spontaneous nystagmus when the patient was in the sitting position, and the head impulse test revealed no catch-up saccade. Additionally, there were no focal neurological deficits found. Examinations of pure tone audiometry revealed normal hearing on both sides. The patient’s eye movement was examined at various head positions and was recorded using a goggle equipped with an infrared camera (SLMED, Seoul, Korea), thus facilitating the “light cupula” diagnosis. A right-beating nystagmus was observed when the patient bowed his head at 90°. While in the supine position, a horizontal nystagmus beating toward the left side was persistently observed, and the maximal slow-phase velocity (SPV) was 33°/s (Figure 1A, Additional file 1). When the patient’s head was turned to the right (Figure 1B, Additional file 2) or left (Figure 1C, Additional file 3) at 90° in the supine position, a geotropic DCPN continued persistently as long as the position was maintained. The intensity of the nystagmus was stronger with head-roll to the left (maximal SPV = 53°/s) than to the right (maximal SPV = 10°/s). A null plane, at which the nystagmus ceases and the direction of nystagmus changes, was identified when the patient turned his head slightly to the right (25 ~ 30°) while in the supine position, leading to a diagnosis of a light cupula on the right side. The diagnostic criteria for the light cupula are the presence of a persistent geotropic DCPN on the supine head-roll test and the identification of a null plane [1]. Magnetic resonance imaging of the brain revealed no abnormal finding.

The patient, after sharing his perspective on the treatment, was prescribed vestibular suppressants for symptomatic relief for one week, and the positional vertigo and nystagmus disappeared within 1 week without adverse effect of the drugs.

Two months later, the patient revisited our clinic with complaints of severe positional vertigo akin to the previously experienced episode of vertigo. Thorough neurological examinations revealed no focal neurologic signs, and the patient’s hearing was normal on both sides. The patient denied alcohol intake within a week before the vertigo attack. A weak spontaneous nystagmus beating toward the right side was observed when the patient was in the sitting position, and a weak left-beating nystagmus was observed when the patient bowed his head at 90°. In the supine position, a right-beating nystagmus was continuously observed, and the maximal SPV was 19°/s (Figure 2A, Additional file 4). When the patient’s head was turned to the right (Figure 2B, Additional file 5) or left (Figure 2C, Additional file 6) at 90° in the supine position, a persistent geotropic DCPN was observed. The intensity of the nystagmus was stronger with a head-roll to the right (maximal SPV = 38°/s) than to the left (maximal SPV = 10°/s). A null plane was identified when the patient turned his head slightly to the left (25 ~ 30°) in the supine position, which led to the diagnosis of a light cupula on the left side.