Critical flicker frequency: Diagnostic tool for minimal hepatic encephalopathy

Background/Aims Minimal hepatic encephalopathy (MHE) is associated with poorer quality of life and increased work disability. Diagnosis requires cumbersome psychometric and neurophysiological tests. We evaluated critical flicker frequency (CFF) to diagnose MHE. Methods 156 cirrhotic patients (age 41 ± 12.5 yr) without overt encephalopathy (Child A 63, Child B 56, Child C 37) were evaluated by psychometric (number connection tests A, B or figure connection tests A, B), P300 auditory event related potential (ERP) and CFF. MHE was diagnosed by abnormal psychometric and/or P300 auditory event related potential. Results Prevalence of MHE was 53% with 27 (43%) in Child’s A, 33 (59%) in Child’s B and 23 (62%) in Child’s C cirrhosis (p = NS). Of 83 patients, 72 (87%) had abnormal psychometry, 64 (77%) had abnormal P300 auditory event related potential (ERP) (380.6 ± 28.8 ms) and in 66 (80%) CFF was below 39 Hz. 60 (83%) patients with abnormal psychometry and 51 (80%) with abnormal P300 auditory event related potential had CFF below 39 Hz. CFF sensitivity (96%), specificity (77%) and positive predictive value (68%), negative predictive value (98%) and diagnosis accuracy was 83.3% when compared to patients with both abnormal psychometry and P300ERP. Conclusions Critical flicker frequency is a simple, reliable and accurate test without any age or literacy dependence for the diagnosis of MHE.