PMC9585182_01
Timeline of the clinical manifestations and treatment progression.
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A 66-year-old man, who presented with paroxysmal weakness of the left lower limb during activities for half a month, was admitted to a local hospital in December 2021 ( Figure 1 ). Magnetic resonance imaging (MRI) examination showed atypical enhancement of the pia meningeal, whereas stereoscopic meningeal biopsy only indicated non-specific inflammatory changes ( Figures 1 ,  2A ). The patient was transferred to our hospital in January 2022 owing to a poor diagnosis ( Figure 1 ). A lumbar puncture examination was performed on the 3rd day after admission ( Figure 1 ). Analysis showed negative results for infectious pathogens, such as herpesviruses, Mycobacterium tuberculosis, HIV, syphilis, and Lyme disease ( Figure 1 ). The patient received oral prednisone acetate (20 mg/day) and azathioprine (150 mg/day) to prevent the recurrence of RM ( Figure 1 ). The patient was generally in good condition, and RM did not relapse during the 1-month follow-up. The patient was instructed to reduce the prednisone dose to 5 mg per day by 5 mg every 2 weeks ( Figure 1 ). After 5 months, the patient was hospitalized for follow-up and was in good physical condition ( Figure 1 ). CSF (6.16 pg/mL), ACPA in serum (>800 U/mL) and CSF (2.8 U/mL), and NMDAR Abs in CSF (1:1), while other indicators were basically normal ( Table 1 ). Considering that the IL-6 and ACPA levels of the patient were still abnormal, he was suggested to increase the dosage of prednisone acetate tablet to 10 mg per day ( Figure 1 ).
A non-specific inflammation and no rheumatoid nodules in the meninges (H&E, scale bar=50 microm, (A). 18F-FDG PET/CT scan showed hypermetabolism of bilateral frontal-parietal meninges and adjacent cortex, especially on the right side (B). NMDAR Abs were absent in serum (scale bar=150 microm, (C)), and NMDAR Abs (1:1) were detected in the CSF (scale bar=150 microm, (D)).
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Magnetic resonance imaging (MRI) examination showed atypical enhancement of the pia meningeal, whereas stereoscopic meningeal biopsy only indicated non-specific inflammatory changes ( Figures 1 ,  2A ). The patient underwent 18F-FDG PET/CT scan, showing hypermetabolism of bilateral frontal-parietal meninges and adjacent cortex ( Figure 2B ). Cell-based assay (CBA) showed the presence of NMDAR Abs IgG in CSF (titer 1:1,  Figure 2D ), while the Abs were absent in serum ( Figure 2C ).
On the first admission, brain MRI showed evident hyperintensity in the leptomeninges of the right frontal and parietal lobes and subtle hyperintensity in the left frontal and parietal lobes in DWI images (A), contrast-enhanced T1-weighted sequences (B), and contrast-enhanced FLAIR sequences (C). MRI conducted at a 1-month follow-up showed subtle hyperintensity of the bilateral frontal and parietal lobes in DWI images (D), contrast-enhanced T1-weighted sequences (E), and contrast-enhanced FLAIR sequences (F).
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Hyperintensity was observed in the leptomeninges of the right frontal and parietal lobes, and subtle hyperintensity was observed in the left frontal and parietal lobes as indicated in the diffusion-weighted image (DWI) ( Figure 3A ), contrast-enhanced T1-weighted sequences ( Figure 3B ), and contrast-enhanced fluid-attenuated inversion recovery (FLAIR) sequences ( Figure 3C ) after examination through brain MRI. T1-weighted sequences ( Figure 3E ), and contrast-enhanced FLAIR sequences ( Figure 3F ).