下眼瞼向き眼振など多彩な ENG 所見を認めた炭酸リチウム服用例

抄録

　A-43-year-old woman with bipolar disorder who was receiving combined therapy with lithium carbonate (400 mg/day) and lamotrigine (100 mg/day) visited us with a history of having recently experienced, on two occasions, sudden wobbling with a fainting sensation, nausea, and vomiting on her way to work. She had no other symptoms, including auditory symptoms. A few hours after she vomited, the symptoms gradually disappeared on both occasions. Subsequently, she has occasionally felt a faint sensation, for instance, when she abruptly stopped to walk. She was also worried about falling while climbing down stairs. MRI revealed no remarkable findings. The serum level of lithium was 0.29 mEq/L, which was within the therapeutic range (0.3-1.2 mEq/L). The characteristic findings on the ENG were as follows: (1) both in light and in the dark, square wave jerks (SWJs) were clearly recognized at the primary eye position; (2) downbeat nystagmus (DBN) was observed mainly at the primary eye position or downward gaze in the dark; (3) the vertical pursuit, especially upward, consisted of saccadic pursuits, while the horizontal pursuit was well preserved; (4) the horizontal and vertical saccades were relatively well preserved. However, post-saccadic drift (glissade) was observed after the upward saccade, and the latency of the downward saccade was slightly delayed; (5) the peak slow phase velocities and frequencies of the horizontal/vertical OKN were reduced; (6) the OKAN was preserved bilaterally, although the SWJs were remarkably intermingled with the OKAN; (7) caloric nystagmus was induced bilaterally; (8) the visual suppression (VS) ratio was reduced bilaterally. These ENG findings mainly suggested dysfunction of the cerebellar systems and deterioration of the neural integrator in the brainstem. The symptoms subsided after discontinuation of the lithium carbonate, and the DBN and postsaccadic drift in the ENG disappeared gradually.

　The present report suggests that lithium intoxication should be considered in the differential diagnosis in a patient taking lithium carbonate presenting with dizziness, whose ENG shows DBN, SWJs and abnormalities of smooth pursuit, OKN, and OKAN.