Neutrophil-to-lymphocyte ratio as a potential differential diagnostic marker for Alzheimer’s disease, major depressive disorder, and Parkinson’s disease

Introduction: Major depressive disorder, Alzheimer’s, and Parkinson’s disease are among the leading causes of dementia in the elderly. These diseases are often misdiagnosed because of overlapping symptoms. This study aimed to evaluate whether neutrophil-to-lymphocyte ratio, which has been used as an indicator of systemic inflammation, can be used for the differential diagnoses of these diseases. Materials and Method: A total of 95 patients with major depressive disorder, Alzheimer’s, or Parkinson’s disease were enrolled. Blood specimens were drawn from participants and neutrophil-to-lymphocyte ratios were calculated. We compared the three groups according to mean neutrophil-to-lymphocyte ratio and mean neutrophil-to-lymphocyte ratio adjusted for age. We used the Receiver Operating Characteristics curve analysis to predict the sensitivity and specificity of this ratio for the differential diagnosis between depression and Alzheimer’s disease. Results: The mean neutrophil-to-lymphocyte ratio for the depression, Alzheimer’s, and Parkinson’s disease groups was 2.2 ± 0.7, 2.9 ± 1.2, and 2.2 ± 0.9, respectively (P = 0.005). The adjusted mean neutrophil-to-lymphocyte ratio for age for the depression, Alzheimer’s, and Parkinson’s disease groups was 2.2 ± 0.17, 2.8 ± 0.15, and 2.2 ± 0.2, respectively (P = 0.025). Receiver Operating Characteristics curve analyses predicted that the sensitivity and specificity for the differential diagnosis between depression and Alzheimer’s disease was 54.8% and 80%, respectively. Conclusion: This study suggested that a simple arithmetic calculation could help clinicians in the differential diagnosis between depression, Alzheimer’s, and Parkinson’s disease. Neutrophil-to-lymphocyte ratio can be used as a secondary line of evidence, along with the initial clinical assessment.