Abstract: A 35yearold female diagnosed with systemic lupus erythematosus (SLE) for more than 14 years, and received longterm immunosuppressive therapy.She was admitted for dizziness with progressive left upper extremity numbness and weakness.Brain magnetic resonance imaging(MRI) shew multiple white matter lesions of hyperintensity on T2weighted and fluid attenuated inversion recovery images, and hypointensity on T1weighted images. JC virus DNA was detectable by the second time nextgeneration sequencing(NGS) test for cerebrospinal fluid(CSF). Progressive multiple leukoencephalopathy (PML) was diagnosed, the dose of immunosuppressant was reduced, and thymosin was used to improve immunity. After that, the patient's neurological symptoms improved and became stable for a long time. This case suggests that neurologic changes in patients with SLE should be alert to this disease.Negative results of JCV test in CSF do not rule out the diagnosis of PML when clinical manifestations and neuroimaging features weve highly suspected. It is necessary to obtain new CSF and make repeat tests.

Key words: progressive multifocal leukoencephalopathy, JC virus, systemic lupus erythematosus, second next-generation sequencing, immunodeficiency