Characteristics of the study population
The study population consisted of 129 patients, including 66 (51.2%) males and 63 (48.8%) females ranging in age from 2 to 62 years with a mean age of 32 ± 12 years. The duration of disease was from 0.1 year to 40 years with an average duration of 12.4 years. The seizure frequency was from 0.5 time/month to 45 times/month with an average frequency 6.6 times/month. There were 60 (46.5%) left TLE cases, and 69 (53.5%) right TLE cases. There were 44 (34.1%) cases with normal MRI results and 85 (65.9%) cases with distinct abnormalities on MRI. AEDs included levetiracetam (LEV), ocazepine (OXC), clonazepam (CZP), valproate (VPA), lamotrigine (LTG), phenytoin (PHT), phenobarbital (PB), carbamazepine (CBZ), topiramate (TPM), and gabapentin (GBP) (Table 1).
Statistical results of factors affecting the interictal discharge patterns
The age of the unilateral discharge group ranged from 2 years to 50 years, with an average age of 29 years, while the age of the bilateral discharge group ranged from 7 years to 62 years, with an average age of 35 years. The difference in age between the two groups was statistically significant (P = 0.02 < 0.05) (Figure 2A). The duration of disease in the unilateral discharge group ranged from 0.1 to 35 years, with an average duration of 11.6 years. The duration of disease in the bilateral discharge group ranged from 0.1 to 40 years, with an average course of 13.5 years. There was no statistically significant difference in the duration of disease between the two groups (P = 0.25 > 0.05) (Figure 2B). In the unilateral discharge group, the seizure frequency ranged from 0.5 time/month to 45 times/month, with an average seizure frequency of 6.8 times/month. In the bilateral discharge group, the seizure frequency ranged from 1 time/month to 30 times/month, with an average seizure frequency of 6.5 times/month. There was no significant difference in the seizure frequency between the two groups (P = 0.84 > 0.05) (Figure 2C). In the unilateral discharge group, there were 21 (28.4%) cases with no clear MRI abnormalities (negative) and 53 (71.6%) cases with clear abnormalities (positive), and the numbers were 23 (41.8%) and 32 (58.2%), respectively, in the bilateral discharge group. The difference in proportion of MRI with or without abnormalities between the two groups was not statistically significant (P = 0.11 > 0.05) (Figure 2D). There were 33 (44.6%) cases which originated in the right temporal lobe and 41 (55.4%) cases which originated in the left temporal lobe in the unilateral discharge group, and 36 (65.5%) cases originating in the right temporal lobe and 19 (34.5%) cases originating in the left temporal lobe in the bilateral discharge group. The difference in proportion of side of origin between the two groups was statistically significant (P = 0.02 < 0.05) (Figure 2E). There were 43 (58.1%) males and 31 (41.9%) females in the unilateral discharge group, and 23 (41.8%) males and 32 (58.2%) females in the bilateral discharge group; however, the difference in gender ratio between the two groups was not statistically significant (P = 0.07 > 0.05) (Figure 2F).
AEDs administered in the unilateral discharge group included LEV, OXC, CZP, VPA, LTG, PHT, PB, CBZ, TPM, and GBP, with CBZ, VPA, and PB being the top three utilized drugs (Figure 3A). AEDs administered in the bilateral discharge group included LEV, OXC, CZP, VPA, LTG, PHT, PB, CBZ, and TPM. The top four utilized drugs were CBZ, VPA, PB, and PHT (Figure 3A). In the unilateral discharge group, there were 10 (13.5%) cases with no AED administration, 39 (52.7%) cases with single AED administration, and 25 (33.8%) cases with administration of multi-AEDs (two or more drugs) (Figure 3B). In the bilateral discharge group, there were 6 (10.9%) cases in whom no AEDs were given, 22 (40.0%) cases in whom a single AED was given, and 27 (49.1%) cases with multi-AED treatment (Figure 3C). There was neither any significant difference in the proportion of cases receiving a single AED vis-a-vis multiple AEDs between the two groups (P = 0.09 > 0.05) (Figure 3D) nor any significant difference between the two groups in terms of the proportion of cases with no AED treatment vis-a-vis AED treatment (P = 0.66 > 0.05) (Figure 3E).
The above data shows that older patients with TLE were more inclined to discharge bilaterally as seen in the interictal EEG. Moreover, right TLE was more likely to be bilateral as seen in the interictal EEG.
Statistical results of ictal diffusion patterns
The site of origin of the seizure and the diffusion direction on ictal EEG in the 129 cases were analyzed. They were classified into 11 diffusion patterns, including unilateral anterior head (6.30%), unilateral anterior head to ipsilateral hemisphere (2.36%), unilateral anterior head to ipsilateral hemisphere to bilateral hemispheres (6.30%), unilateral anterior head to bilateral hemispheres (35.43%), unilateral anterior head to bilateral anterior heads (3.94%), unilateral anterior head to bilateral anterior heads to bilateral hemispheres (17.32%), bilateral anterior heads (1.57%), bilateral anterior heads to bilateral hemispheres (11.81%), bilateral hemispheres (12.60%), unilateral hemisphere (1.57%), and unilateral hemisphere to bilateral hemispheres (0.79%) (Figure 6C). It could be seen that in TLE, the side of origin can be located by scalp EEG most of the time, and the spread of ictal discharge in the EEG in most cases had a wide diffusion range, with most of them having bilateral hemispheric involvement. The cases with interictal unilateral discharge showed all 11 ictal diffusion patterns described above (Figure 6A), while the cases with interictal bilateral discharge showed only 8 patterns (Figure 6A).
When analyzed according to the side of TLE, the ictal diffusion patterns in right TLE included the first nine ictal diffusion patterns mentioned above (Figure 4A through 4G, Figure 6B), and the ictal diffusion patterns in left TLE had all 11 of the patterns described (Figure 5A through 5I, Figure 6B). On statistical analysis, there was no significant difference between the unilateral discharge group and the bilateral discharge group in the ratio of ictal EEG limited to the ipsilateral hemisphere to ictal EEG where the seizure had spread to both hemispheres (P = 0.12 > 0.05) (Figure 6D). However, there was a statistically significant difference in this ratio between right and left TLE (P = 0.02 < 0.05) (Figure 6E). This demonstrated that right TLE was more likely to spread to bilateral hemispheres during seizures.