Positional alcohol nystagmus and serum osmolality: New insights into dizziness associated with acute alcohol intoxication.

Positional alcohol nystagmus (PAN) is characterized by positional direction-changing nystagmus. Although the buoyancy cupulopathy, which implies that the cupula becomes lighter or heavier than the endolymph due to different diffusion rates of alcohol, has been accepted as possible mechanism of PAN, the evidence supporting this hypothesis is weak. The aim of present study is to investigate the possibility of serum osmolality change following alcohol intake as a cause of PAN. Nine healthy adults were recruited voluntarily. Positional nystagmus was examined before and every 1 hr after alcohol intake until 7 hr. Serum osmolality was measured before and 1 and 7 hr after alcohol intake. Before ingesting alcohol, no subject showed positional nystagmus, and mean serum osmolality was 285.9 ± 4.4 mOsm/kg. At 1 hr after drinking, mean serum osmolality increased to 302.9 ± 8.9 mOsm/kg, and all subjects exhibited geotropic positional nystagmus. At 7 hr after drinking, mean serum osmolality decreased to 289.1 ± 9.4 mOsm/kg, and all subjects showed ageotropic positional nystagmus. Change in serum osmolality following alcohol ingestion and subsequent change in specific gravity in the perilymph and endolymph may be a cause of PAN.