Comparison of critical flicker frequency test (CFF) value with normal population in patients with alzheimer's

Background and aim: Alzheimer's disease (AD) is the most common cause of dementia in elderly. Although the difficulty in remembering new information is the most common symptom in early stages, as the disease progresses, cognitive impairment deepens and daily basic life activities deteriorate. AD treatment is still insufficient despite all the recent developments, but early detection and treatment in early stage of disease has been shown to provide more clinical benefit. In this study, we aimed to use the Critical Flicker Fusion Threshold (CFF) test to diagnose Alzheimer's disease in early stage. The CFF is a well understood neurophysiological test that measures the ability of the central nervous system to detect flickering light in relation with direct cortical activity. Materials and Methods: In this study, 120 patients and 50 control groups were included who admitted to Gaziantep University Sahinbey Research and Application Hospital Geriatrics outpatient clinic and diagnosed as early and middle stage Alzheimer's disease over 65 years of age. A history of visual and hearing impairment, advanced cardiovascular system and respiratory system diseases, chronic liver disease, diseases with severe metabolic disorders, patients with advanced stage dementia and drug use affecting the central nervous system were excluded from the study. The remaining 58 patients and 25 healthy volunteers underwent comprehensive geriatric assessment and CFF testing. Findings: Fifty eight patients and twenty five healthy volunteers were enrolled in this study. The mean age of patients was 70.1 ± 7.6 and the male to female ratio was 26/32. The mean age of control group was 68.5 ± 6.4 and the male to female ratio was 13/12. The mean of CFF of AD group was significantly lower than control group (36.44±7.00 vs 44.24±3.82, p<0.001, respectively). There was a significant difference in standardized mini-mental test score in both groups (18.05±5.25 vs 25.96±2.85, p<0.001, respectively). There was also a positive correlation between CFF value and standardized mini-mental test score (p<0.001, r=0.459). Thirty four were early stage and twenty four were mid-stage of AD group. There was a significant difference in CFF values between the three groups when we compared the patients as early and mid-stage Alzheimer's and control groups (p<0.001). The mean CFF value in early-stage Alzheimer's patients was 37.93 ± 7.33. It was 34.97 ± 7.43 in the middle-stage patients. The mean age, gender, education level and the number of drugs used did not show a statistically significant difference in both groups (p>0.05). The cut-off value for the CFF variable was determined as 39 in the ROC analysis. (p<0,001; AUC=0,852; Sensitivity=70,69% (95% CI 57,3-81,9); Specificity=92,00% (95% CI 74,00-99,00) ) . Results: There is a significant difference between AD and healthy group's mean CFF values. CFF may play an important role in diagnosis of Alzheimer's disease in the early stage. Our study is the first and only study in literature which gives a cut-off value for CFF in AD. The important advantages of the test are that the applicability is simple and practical as well as noninvasive and cost-effective. It does not differ according to age, gender and education level. CFF testing can be used as an important diagnostic method in patients with Alzheimer's disease, when considering characteristic history and clinical findings.