Table 1.

The symptoms and treatment in the patient according to timeline.

Symptoms and examination	Time	Treatment
Intermittent headache; fatigue;	2021-10-7	Without treatment
Intermittent headache, neck pain; fatigue	2021-11-1
Gait ataxia.	2021-11-16
Head shaking uncontrollably from side to side (Supplementary Video 1 and Figure 1A); Gait ataxia (Supplementary Video 2).	2021-11-18
The patient could not complete heel-knee-tibia test and finger-nose test stably, and presented moderate limb dysmetria, Romberg sign and horizontal nystagmus. The patient also could not walk in a straight line.	2021-11-20 Hospitalization	Ganciclovir for injection was administered and sustained by 0.375 g twice a day.
Increased signal in the right cerebellar hemisphere without enhancement	2021-11-20 Brain magnetic resonance imaging (MRI)
WBC count:139 × 10 6 /L (Figure 2); protein level:1.67 g/L.	2021-11-22 Lumbar puncture
	2021-11-24	Anti-Homer-3 antibody titers of 1:3.2 in the CSF and 1:100 in the serum (Figure 1).
	2021-11-24	Methylprednisolone for injection was administered by 1,000 mg per day, and reduced by half every three days. Immunoglobin was administered by 25 g per day for 5 days (2 g per kilogram).
Gait ataxia, head shaking and horizontal nystagmus improved.	2021-11-30
Gait ataxia, head shaking and horizontal nystagmus still improved.	2021-12-3	Mcophenolate mofetil was given and sustained by 0.5 g twice a day. Methylprednisolone was administered by 120 mg per day for 3 days.
The heel-knee-tibia test, finger-nose test and moderate limb dysmetria improved.	2021-12-6	Prednison was given by 60mg per day, and reduced by 5mg every two week.
Anti-Homer-3 antibody titers of 1:3.2 in the CSF and 1:100 in the serum. WBC count: 55 × 10 6 /L; protein level: 0.91 g/L. Horizontal nystagmus was not observed. Gait ataxia and head shaking was still observed (Supplementary Video 2).	2021-12-9 Lumbar puncture
Head shaking disappeared.	2021-12-15
The improvement of gait ataxia was not remarkable. The patient still could not walk in a straight line.	2021-12-25	Another immunoglobin was administered by 25 g per day for 5 days (2 g per kilogram).
Normal	2022-1-5 Brain MRI
WBC count: 29 × 10 6 /L; protein level: 0.75g/L.	2022-1-13 Lumbar puncture	Ganciclovir and mcophenolate mofetil was administered and sustained.
Although the patient improved remarkably, mild gait ataxia and unbalance during walking in a straight line were still observed (Supplementary Video 2). The patient could complete both hands alternating movement test, heel-knee-tibia test and finger-nose stably, and did not present Romberg sign. Another lumbar puncture was not received by the patient.	2022-1-25 Hospital discharge	Acyclovir tablets were given by 0.4 g three times a day for two weeks. Mcophenolate mofetil was given and sustained by 0.5 g twice a day. Prednison was given by 50 mg daily, and reduced by 5 mg every two weeks.