IgG index of cerebrospinal fluid can reflect pathophysiology associated with Lewy bodies in Parkinson's disease

Background: Neuroinflammation is one of the pathophysiologies of Parkinson's disease (PD). Lewy bodies, the pathological hallmark of PD, emerge as a consequence of α-synuclein aggregation, and neuroinflammation is induced concurrently with this aggregation. Imaging and cerebrospinal fluid (CSF) biomarkers that reflect PD pathophysiology have been developed or are under investigation. The IgG index of CSF is a marker of inflammation, and may also reflect the pathophysiology of PD. Aim: We examined if the IgG index reflects the pathophysiology of PD in drug-naïve PD patients. Method: The subjects were 20 consecutive PD patients who underwent ¹²³I-MIBG scintigraphy for assessment of the heart to mediastinum (H/M) ratio and wash out rate, ¹²³I-Ioflupane SPECT for examination of the specific binding ratio in the striatum, and lumbar puncture before treatment. The CSF IgG index and levels of pathogenic proteins (total α-synuclein, oligomeric α-synuclein, total tau, phosphorylated tau and amyloid Aβ1–42) were determined. The IgG index was compared with the other parameters using Spearman correlation analysis. Results: The IgG index showed a significant correlation with the H/M ratio in early (r = −0.563, p = 0.010) and delayed (r = −0.466, p = 0.038) images in ¹²³I-MIBG scintigraphy and with the CSF total tau level (r = −0.513, p = 0.021). Conclusion: Neuroinflammation is involved in PD pathophysiology in some patients, and a higher IgG index indicates the presence of neuroinflammation accompanied by emergence of Lewy bodies.