Twenty patients (group I) with IIH were examined. Patients were diagnosed according to Dandy criteria for diagnosis of IIH disease. Twenty healthy subjects, matched for age, sex, and level of education, represented the control group (group II). All patients of group I and subjects of group II gave informed consent to share in this study. The study was officially approved by two appropriate ethical committees (intradepartmental and faculty ethical committees).
Group I included patients with a score greater than or equal to 24 on mini-mental state examination (MMSE), having intracranial pressure greater than 25 cmH2O measured in lateral decubitus position, showing normal CSF composition, and the absence of hydrocephalus or mass in imaging. Ages ranged from 18 to 45 years, and education started at 6 years or more. The study excluded patients with major language disturbance; severe physical, auditory, or visual impairment affecting their ability to complete testing; those with a history of alcohol intake or any substance abuse, with evidence of any concomitant medical or metabolic illness known to affect cognition—e.g., thyroid or parathyroid disease, hepatic or renal failure; those with current or prior history of major psychiatric disorder and/or current use of anxiolytic, neuroleptic, or sedative medication; and—finally—those with known comorbidities such as hypertension or diabetes mellitus.
The MMSE assesses subjects’ orientation to time and place, instantaneous memory, short-term memory, serial subtractions or reverse spelling constructional capacities (copying a design), and use of language (Folstein et al. 1975). Clinical assessment was carried out for the patients, and it included general examination, with different systems assessment to exclude any associated medical illness, as well as thorough history taking and full neurological examination, according to the IIH sheet of the local Neurology Department (Additional file 1: Appendix 1).
Neurophysiologic tests performed for both groups included P300, as well as CNV (Additional file 3).
The machine used to record both responses was Neuropack MEB-9200 G/K EP/EMG measuring system four-channel, version 08 (Neuropack M1); manufacturer: Nihon Kohden, Tokyo, Japan). The active electrode was placed at CZ according to the 10–20 international system of electroencephalography electrode placement, the reference electrode was placed over either mastoid process, and the ground electrode was placed on the forehead. For the P300 test, the auditory oddball paradigm was carried out, after determining the hearing threshold for each subject. Two hundred auditory stimuli (bursts) were presented to the ears through earphones, with an intensity of 60 dB above the hearing threshold; 80% of tones were 2 kHz in frequency (background tones), whereas the remaining 20% were 8 kHz (target tones). These tones presented randomly intermixed at a rate of 0.5/s. The wave P300 was defined as the most positive point of the average waveform to the target tones after 250 ms and before 500 ms. However, for the CNV, a single click elicits a brief positive peak and a brief negative peak. On the other hand, when a single click is followed by repetitive flashes that are terminated by a button press, there is another large gradual negative peak, which ends sharply with the button press. This is the CNV methodology used in the study. The CNV appears after about 30 trials of paired stimuli, although this number can be reduced when the subject understands the task in advance.
Statistically, the data were analyzed using IBM SPSS advanced statistics (version 22; SPSS Inc., Chicago, IL, USA). Numerical data were expressed as mean and SD or median and range as appropriate. Qualitative data were expressed as frequency and percentage. χ2 test or Fisher’s exact test was used to examine the relation between qualitative variables. For non-normally distributed quantitative data, comparison between two groups was done using Mann–Whitney test (nonparametric t test). Spearman’s method was used to test correlation between numerical variables. All tests were two-tailed. The descriptive analysis of the results is as follows: The data were summarized using minimum, maximum, mean, and SD for quantitative data and the frequency distribution for qualitative data. The probability/significance value is as follows: P value greater than or equal to 0.05 was not significant, whereas P value less than 0.05 was significant. A correlation is a single number that describes the degree of relationship between two variables.
The most common type is the Pearson correlation. The sign of correlation coefficient (+, −) defines the direction of the relationship, either positive or negative. A positive correlation coefficient means that as the value of one variable increases, the value of the other variable increases; as one decreases, the other decreases. A negative correlation coefficient indicates that as one variable increases, the other decreases, and vice versa.
