Clinical and Electrophysiological Differences between Subjects with Dysphonetic Dyslexia and Non-Specific Reading Delay

Abstract

Reading is essentially a two-channel function, requiring the integration of intact visual and auditory processes both peripheral and central. It is essential for normal reading that these component processes go forward automatically. Based on this model, Boder described three main subtypes of dyslexia: dysphonetic dyslexia (DD), dyseidetic, mixed and besides a fourth group defined non-specific reading delay (NSRD). The subtypes are identified by an algorithm that considers the reading quotient and the % of errors in the spelling test. Chiarenza and Bindelli have developed the Direct Test of Reading and Spelling (DTRS), a computerized, modified and validated version to the Italian language of the Boder test. The sample consisted of 169 subjects with DD and 36 children with NSRD. The diagnosis of dyslexia was made according to the DSM-V criteria. The DTRS was used to identify the dyslexia subtypes and the NSRD group. 2⁻5 min of artefact-free EEG (electroencephalogram), recorded at rest with eyes closed, according to 10⁻20 system were analyzed. Stability based Biomarkers identification methodology was applied to the DTRS and the quantitative EEG (QEEG). The reading quotients and the errors of the reading and spelling test were significantly different in the two groups. The DD group had significantly higher activity in delta and theta bands compared to NSRD group in the frontal, central and parietal areas bilaterally. The classification equation for the QEEG, both at the scalp and the sources levels, obtained an area under the robust Receiver Operating Curve (ROC) of 0.73. However, we obtained a discrimination equation for the DTRS items which did not participate in the Boder classification algorithm, with a specificity and sensitivity of 0.94 to discriminate DD from NSRD. These results demonstrate for the first time the existence of different neuropsychological and neurophysiological patterns between children with DD and children with NSRD. They may also provide clinicians and therapists warning signals deriving from the anamnesis and the results of the DTRS that should lead to an earlier diagnosis of reading delay, which is usually very late diagnosed and therefore, untreated until the secondary school level.

Keywords: QEEG; direct test of reading and spelling (DTRS); dysphonetic dyslexia; non-specific reading delay; quantitative EEG tomography; source localization, VARETA, Biomarkers.

Figure 1

Results of the t-test between DD and NSRD groups for the Z-EEG spectra at all leads and frequencies. Main significant differences are an excess of activity of the DD group in the middle line in almost all frequency bands and a reduction of fast activity in the left fronto-parietal and temporal leads.

Figure 2

Significant differences of the t test at the sources spectra of DD vs NSRD. Red and yellow values indicate an excess of DD compared to NSRD; values in the blue scale indicates excess of NSRD compared to DD. Threshold corrected by multiple comparisons. Differences are concentrated in very narrow bands of frequencies. In general, DD have an excess of slow activity (Delta and slightly Theta) and a defect of fast activity (Beta band).

Figure 3

Scatterplot showing the individual scores obtained by the classification equation of the DTRS variables, for the subjects of the two groups NSRD (unspecific reading delay) and DD (dysphonetic dyslexics). For each group a boxplot with the mean and standard deviation of the individual values is shown.

Figure 4

rAUC for the classification equation showing a value of 0.94, which indicates almost perfect sensitivity and specificity. The three panels at the right show the density functions of the total rAUC as well as the discrimination power at the 10% and 20% of False Positives, obtained by the 500 random realizations. The discrimination power at the 50% of the density function was of 0.87 for the 10% of False Positives and 0.93 at the 20% of False Positives.