A group of 167, 103 males, aged 4.9-28.4 years who have completed ALL therapy was enrolled to the study. The study group was divided into 3 subgroups according to treatment protocols introduced gradually by Polish Leukemia/Lymphoma Study Group. The first group consisted of 35 patients (21 boys, 60%) who received treatment according to modified New York programs (NY). The second group of 47 patients (24 boys, 51.1%) were treated with previous modified BFM protocols (pBFM): BFM 81, 83, 86 and 87. In those two groups optionally, therapeutic central nervous system radiotherapy was conducted. The last group consisted of 85 patients (40 males, 47.1%) underwent treatment with BFM95 protocol without radiotherapy. There were no symptoms of hearing, sight and sensory perceptions disorders in participants. ALL relapse has not been registered in the study population. The central nervous system involvement was confirmed in 7 cases (1 – NY, 5 – pBFM and 1 – BFM95, respectively).
Cumulative doses of vincristine in NY protocols amounted 26 to 89 mg/m2 (60.8 mg/m2 on average) and 30 mg/m2 in BFM protocols. The radiotherapy dose in pBFM group was 13-36.4 Gy (mean 18.4 Gy), while in the group treated with NY protocols - 18.2-24 Gy (mean 18.3 Gy).
The control group consisted of 35 patients (18 males, 51.4%), aged 6 - 17 years. They were patients of Neurology Department (children with educational difficulties, emotional disorders, children after a single syncope episode) and general healthy volunteers which were neurologically consulted.
The study protocol was complied with the Declaration of Helsinki and was approved by the Jagiellonian University Medical College Ethics Committee (Consent No. KBET/131/B/207). All parents as well as adolescent and adult patients signed written informed consent before inclusion in the study.
2.1 Auditory evoked potentials methodology
Examination was performed in comfortable semi-sitting position on armchair with back and head support. The stimulation was performed by headphones with use an acoustic impulse. In first, an electrophysiological hearing threshold was estimated. Next, both ear canals were stimulated alternately by repetitive (10 Hz) acoustic stimulus (click) at 70 dB above hearing threshold. During it other ear was masked by murmur at 40 dB lower than acoustic stimulus. BAEP were recorded by using cup electrodes placed according to 10-20 international system. Detected waves were analyzed by comparing impulses from stimulated or not stimulated ear with those from a vertex. Used filter excluded frequencies below 150 Hz and above 300 Hz. Recorded 1000-2000 responses were averaged twice. According to guidelines of International Federation of Clinical Neurophysiology (IFCN) only curves with differences less than 0.1 ms in latencies and less than 10% in amplitudes between waves were taken into consideration. Waves I, III and V, their latencies and also interwave latencies between waves I-V, I-III, III-V were evaluated. Recorded results were compared with normal values based on our own material. Latencies and interwave latencies elongation more than 2 SD were assumed as abnormal. To evaluate the effect of treatment, comparisons of ALL patients (NY, pBFM, BFM95) were made with the control group. Additionally, to evaluate impact of radiotherapy a group of patients receiving radiotherapy (NY and pBFM) was compared to non-irradiated (BFM95).
2.2 Visual evoked potentials methodology
All patients were examined in comfortable position in shady room (about 50 lux). Before examination all patients have been evaluated for visual acuity. VEP were examined according to IFCN guidelines with using “pattern reversal” method. Black and white chessboard-like pattern with specified dimension as 16 minutes of arc, was moving in sequence with frequency of 2 Hz. A monitor was a 1 m in front of patient’s eyes. Average luminance of stimulator in middle of a stimulation area was 50 cd/m2. In study were used: Recording electrode placed in middle of occipital area, references electrodes in middle line on forehead in first scheme and two on auricles in the others and zero electrode on vertex. Used filter excluded frequencies below 0.3 Hz and above 300 Hz. Time of analysis was from 250 to 450 ms. At least 100 measurements were averaged. From obtained curve, positive (N70, N135) and negative (P100) were isolated for further analysis of their latencies and amplitudes. Only pairs of curves were evaluated in which the latency of the P100 wave did not differ by more than 2.5 ms.
2.3 Somatosensory evoked potentials methodology
The SEP analysis was performed in accordance with IFCN recommendations. The median nerve was stimulated with repeated rectangular electric stimulus from electrode placed in wrist area, with duration of 200 µs, frequency 5 Hz and intensity exceeding 3 times the threshold stimulus causing the sensory response. Response was recorded by 4 cup electrodes. In every case, before stimulation an electrode resistance was measured (lower than 500 ohms). Recorded frequencies below 20-30 Hz and above 3000 Hz were excluded. Average time of analysis was 50 ms. Depending on the legibility of the waves, 500-2000 responses were averaged. In every case 2 similar entries were recorded in which the latency differ not more than 0,25 ms and amplitudes no more than 20%. Amplitudes and latencies of above described waves were analyzed and compared to control group. Peripheral (PCT) and central (CCT) conduction times were estimated for differentiation. Results of examination was compared to our normal values based on own material. SEP waves with latency and interlatency elongation more than 2 SD and/or amplitudes less than 1 SD were assumed as abnormal. P14 waves were not analyzed due to high variability in the control group.
2.4 Statistical Analysis
Statistical analyses were performed with Statistica 12.0 (StatSoft, Statistica 12.0, Tulsa, Oklahoma, USA) software. Continuous variables are expressed as mean ± standard deviation and categorical variables as number (percentage). Continuous variables were first checked for normal distribution by the Shapiro-Wilk statistic. Differences among two groups were compared by student's t-test when normally distributed or by the Mann-Whitney test with test for non-normally distributed variables. In turn, differences among the three groups were compared by ANOVA test when normally distributed or by the Kruskal-Wallis test with test for multiple comparisons for non-normally distributed variables. Categorical variables were analyzed by the chi-square test and Fisher's exact test depending on the size of the analyzed groups. P-value of less than 0.05 was considered statistically significant.