Sensitivity and Specificity of the Diagnostic Method for Detecting α-Synuclein as a Histological Marker for Parkinson's Disease in Salivary Gland Tissues: a Systematic Review and Meta-analysis

Abstract

Immunohistochemistry of α-synuclein (α-syn), a marker for Parkinson's disease, in salivary gland (SG) biopsy specimens has been actively studied as a method of verification and early diagnosis. This systematic review and meta-analysis aim to analyze characteristics of study designs and evaluate pooled sensitivity and specificity. The review included publications that were found by keyword search and met inclusion criteria. The meta-analysis of comparative studies was conducted using a univariate random-effects model to calculate pooled specificity and sensitivity. The systematic review and meta-analysis included 16 and 13 clinical studies, respectively. Antibodies against modified α-syn, double detection, and incisional biopsy specimens of SGs were the most common approaches used in the studies. There is a need for clinical studies with quantitative data analysis. Approximately 15% of patients experienced adverse events, which were more common in case of fine-needle aspiration biopsy specimens of SGs. Pooled sensitivity and specificity (regardless of the anti-α-syn antibody type and SG size) were 76.6% and 98.0%, respectively. Sensitivity (76.3%) and specificity (99.3%) were higher when antibodies against phosphorylated α-syn and major SGs were used. The most promising variant of the method involved double detection using antibodies against modified α-syn and markers of nerve fibers in incisional biopsy specimens of major SGs and quantitative data analysis. The meta-analysis revealed a possibility of developing this diagnostic method and implementing it into routine practice owing to its high sensitivity and specificity. Further studies employing quantitative data analysis are required to gain deeper insight into the method's role in verifying Parkinson's disease and informing the severity of neurodegeneration and disease prognosis.