Fig. 1

Videonystagmographic recordings of a patient with periodic alternating nystagmus responsive to intravenous immunoglobulins. a Horizontal slow-phase velocity (HSPV) recording at admission showed a maximum speed of 6.3°/s in light. b HSPV recording at admission exhibited a maximum speed of 30.7°/s in the dark. c.1–c.3 Horizontal eye position (HEP) for each eye movement is plotted against time in the dark. c.1 Under the effect of clonazepam alone showed PAN with a periodicity of 12 s comprised of 5 s of right-beating nystagmus and a 2-s steady phase followed by 5 s of left-beating nystagmus. c.2 During the use of clonazepam and intravenous immunoglobulins, in which no nystagmus is observed. c.3 During the use of clonazepam and 3 months after the last dose of intravenous immunoglobulins, PAN appeared again with similar characteristics as in c.1