Neurophysiological study and use of P300 evoked potentials for investigation in the diagnosis and follow-up of patients with Alzheimer's disease

Introduction and objectives. At the present time the diagnosis of Alzheimer's disease (EA) is based on clinical evaluation of the symptoms and various complementary investigations mainly directed towards ruling out secondary dementias. However, definite diagnosis can only be made on cerebral biopsy. We wished to evaluate the efficacy of different neurophysiological investigations used in the diagnosis and follow-up of EA. Patients and methods. After drawing trp a table of normal values, we selected a samples of 33 patients with suspected EA. Following assessment-clinical, neuropsychological(Mini-Mental State Examination -MMSE-) and neurophysiological (electroencephalography -EEG-, P300 potentials, reaction time and rate of error)-, the patients were classified as having probable EA, possible EA or other dementia according to the criteria of NINCDS-ADRDA. Statistical analysis was done on the series of cases studied. Results. In our experience, the most interesting findings were obtained from the EEG, MMSE and latency of the P300 evoked potentials. The most useful neurophysiological parameters for help in diagnosis of EA was the P300 latency, with a sensitivity of 77% and a specificity of 83%. The MMSE seems to show the degree of cognitive deterioration better, whilst the P300 latency seems to behave as a marker of a characteristic feature of the disorder. Conclusion. The P300 latency is very useful in diagnosis, since it is found to be altered in cases with EA at an early stage, with very little cognitive degeneration and even with a score of 30 on the MMSE.