Stroke is an important neurologic emergency that may lead to serious morbidity and mortality, although it is observed more rarely in childhood than in adults. The World Health Organization defines stroke as “a rapidly developing set of clinical findings due to focal or global impairment of cerebral functions, lasting longer than 24 h or resulting in death” (1). While the etiologies of stroke in the pediatric population spread over a wide spectrum, hereditary metabolic diseases are among the rarer causes. Nevertheless, they have special importance in terms of the need for early diagnosis and specific treatment (2, 3). SLE are characterized by acute or subacute onset neurologic findings do not conform to single vascular territory (4). The best-defined example in the mitochondrial disease group with SLE is MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) syndrome (5). In addition, Kearns-Sayre syndrome, Leigh syndrome, MERRF, LHON (Leber’s hereditary optic neuropathy), and non-syndromic mitochondrial diseases, especially POLG mutations, have also been associated with similar clinical pictures (6, 7). The clinical spectrum is quite broad. While migraine-like headaches and epileptic seizures are frequently seen before the episode, various symptoms, including altered consciousness, hemiparesis, aphasia, cortical visual loss, and neuropsychiatric findings, may occur in the acute phase of the episode (7, 8). On imaging, lesions are frequently localized in occipital, parietal, or posterior temporal lobes, limited to the cortex, asymmetric, and incompatible with vascular distribution (4, 9). Electroencephalography (EEG) findings contribute to the diagnosis of encephalopathic changes and focal epileptiform activity (10). Treatment aims to reduce metabolic stress, ensure seizure control, and avoid agents with the potential for mitochondrial toxicity. L-arginine treatment administered in the acute period has been reported to provide symptomatic improvement in some patients (11, 12).

In this study, we retrospectively evaluated the clinical, laboratory, imaging, and EEG characteristics of SLE in children with molecularly confirmed mitochondrial disease who were followed up in nine different pediatric metabolic centers across Turkey.

The retrospective medical records of 34 patients who were followed up in the pediatric metabolism and nutrition divisions of nine centers in the Marmara Region in Turkey were analyzed. Inclusion criteria were children and young adults with a genetically confirmed mitochondrial disease and at least one follow-up visit in the participating centers. Exclusion criteria were incomplete molecular diagnosis or lack of accessible clinical data. Current age, age at first episode and age at diagnosis, clinical features, growth parameters, laboratory, radiological, EEG and molecular analysis findings were recorded. For cases with incomplete EEG or MRI data, the available findings were included and explicitly noted as missing when absent. To ensure comparability, standardized data collection templates were used across all nine centers, and case information was harmonized by a coordinating investigator. The data obtained in the study were analyzed using SPSS 23 (Statistical Package for Social Sciences) software. In statistical analyses, Chi-square analysis and Fisher Exact test were used to examine the relationships between categorical variables. Kruskal-Wallis test and Mann- Whitney U test were used to evaluate the differences between continuous variables since parametric test assumptions were not met. In all analyses, the significance level was determined as p < 0.05 and the confidence level was evaluated as 95%. Ethical approval was obtained from the Tekirdağ Dr. İsmail Fehmi Cumalıoğlu City Hospital Clinical Research Ethics Committee (Decision no. 2024/119). Research was conducted accordance with the Declaration of Helsinki.

In this multicenter observational cohort study, the clinical, radiological, EEG, and genetic features of genetically diagnosed mitochondrial diseases, the frequency of stroke-like episodes, associated findings, and L-arginine treatment were evaluated. In a study by Ng YS and colleagues on the prediction of stroke-like events and outcomes in mitochondrial diseases, 111 patients aged 1–72 years diagnosed with mitochondrial disease were retrospectively evaluated (13). This study indicated that stroke-like episodes in mitochondrial diseases are also seen in the paediatric age group. In our study, we evaluated paediatric patients who experienced stroke-like episodes associated with mitochondrial disease. Although the data obtained were generally consistent with the existing literature, they also showed some remarkable differences. SLE were most frequently observed in individuals diagnosed with MELAS (44.1%), as reported in the literature (11). In the majority of these patients (66.6%), m.3243A > G mutation was found in the MT-TL1 gene, and this rate was consistent with previously reported data (14). POLG mutation stood out as the second most common cause of SLE, and this was consistent with the frequency ranking in the literature (13). Coenzyme Q10 (CoQ10) deficiency is one of the rare mitochondrial disorders that develop due to mutations in genes involved in ubiquinone synthesis. In the literature, there are a limited number of cases and small patient series in which SLE have been reported to be associated with mutations in biosynthesis genes such as COQ8A (ADCK3) and COQ4 (15, 16). In our study, SLE were observed in two of nine patients diagnosed with CoQ10 deficiency. This finding indicates that CoQ10 deficiency may rarely lead to SLE and emphasizes that neurologic symptoms should be carefully evaluated in this patient group. SLE associated with Leigh syndrome have rarely been described in the literature. In a case report, a three-month-old female infant with post-infectious encephalopathic features and neurologic symptoms, including hypotonia, apnea, and optic atrophy was diagnosed with Leigh syndrome. This case suggests that metabolic stress may trigger neurologic findings in Leigh syndrome, and the disease may present with stroke-like episodes (17). In our series, it was observed that two of the four patients with Leigh syndrome developed stroke-like episodes in relation to metabolic stress. This observation reveals that Leigh syndrome may present not only as a progressive neurodegenerative disorder but also with acute neurologic decompensations triggered by metabolic stress. It emphasizes the necessity for early diagnosis, close follow-up, and prevention of metabolic crises in this patient group. In a study conducted by Durrleman et al. (18) on 60 pediatric patients, it was reported that the first symptoms of the patients started between 0 and 28 months, and the first SLE occurred between 17 and 124 months. In a study conducted by Ng et al. (13) on Forecasting stroke-like episodes and outcomes in mitochondrial diseases, it was noted that 32% of patients experienced their first stroke episod after the age of 40. In our study, it was observed that the first symptoms usually started before the age of 5 years, and the first SLE occurred mostly in the age range of 5.01–10 years (38.4%). The youngest patient was 1.9 years old, and the oldest patient was 40 years old. This shows that the development of episodes is not limited by age and can occur at any age. Gender distribution was equal (F/M: 7/7), and gender was not a determining factor in episodes. In this respect, it differs from some studies in the literature (18). An analysis of the clinical symptoms revealed that headache was prevalent before a SLE. This was followed by decreased muscle mass, myopathy, and seizures. In a study by Xu et al. (14) involving children with MELAS syndrome, muscle weakness was defined as an indicator of severe mitochondrial dysfunction. In studies, seizures are frequently reported as the first symptom of SLE. In mitochondria-damaged cells, the increased metabolic demand associated with excessive neuronal activity during seizures cannot be met. This leads to local energy deficits, ion imbalances, and intracellular lactic acid accumulation. This situation can cause cell damage, vascular irregularities, and associated SLE. The high seizure frequency found in our study and its significant association with stroke- like episodes support the hypothesis that these episodes may be triggered by epileptic seizures (14, 18). In a study conducted by Ng et al. (13) on MELAS patients, it was reported that 91% of the patients had symptoms indicating mitochondrial dysfunction before the SLE, and the most common symptom was sensorineural hearing loss. In our series, findings such as hearing loss, cortical blindness, recurrent vomiting, and myopathy were frequently observed before SLE in individuals diagnosed with MELAS. In addition, sensorineural hearing loss was one of the most common symptoms in these patients. Although no statistical significance was found between SLE and some demographic variables such as age, gender, and BMI, low BMI in MELAS and Leigh patients is remarkable. This indicates that short stature and nutritional deficiency also accompany these patients and is in parallel with the literature (13). Studies have shown that brain lactate levels increase with disease progression in MELAS patients, and this increase reflects a progressive shift in oxidative redox potential. These findings suggest that lactate levels may be an important biomarker for monitoring the course of the disease and establishing a diagnosis (19). While studies suggested that lactate levels may be an important biomarker for monitoring the course of the disease and establishing a diagnosis, the variation does not clearly dichotamise those with or without stroke like episodes in our study. In radiologic evaluations, Durrleman et al. (18) reported that bilateral cortical diffusion hyperintensity and hyperperfusion were prominent in cranial MR images obtained in the first 48 h, and this condition developed due to energy metabolism disorders different from classical ischemic strokes (13). In our study, bilateral lesions were observed in all seven patients imaged in the acute period, and the most common site of involvement was frontotemporal lobes. When EEG findings were analyzed, focal epileptiform activity was found to be more frequent in accordance with the literature (13). Regarding the use of L-arginine treatment, a retrospective analysis by Ganetzky et al. (20) reported that clinical improvement was achieved in 47% of patients who received intravenous (iv) arginine treatment. A better response to treatment was observed, especially in cases of hemiplegic attacks. In our series, six patients with SLE received iv arginine treatment in the acute phase of the episode, and clinical improvement was observed. Seven of our patients who did not receive L-arginine treatment (3 POLG, 2 MELAS, 1 Coenzyme Q10 deficiency, 1 Leigh) experienced prolonged headaches, nausea and visual impairment. In Durrleman et al.’s (18) study, recurrent stroke-like episodes were reported in three patients over an eight-year follow-up period, whereas in our series, six patients experienced recurrent stroke-like episodes, with five episodes recorded in one MELAS patient and four in another. In systematic reviews on the efficacy of oral L-arginine treatment, it was emphasized that the clinical benefit of acute or prophylactic use was limited, but methodological deficiencies were found in these studies (21). In a study including six MELAS patients, it was reported that oral L-arginine treatment at a dose of 0.15–0.3 g/kg/day administered for 18 months resulted in significant improvement (22). In our study, 4 of our 13 patients with SLE continued long-term oral L-arginine treatment. Six of our MELAS patients without SLE also received long-term oral L-arginine treatment. While no episodes were observed in 6 of these patients, a median of 2 attacks were observed in 4 patients.

The study is robust in its examination of SLE in paediatric mitochondrial cases with molecular diagnosis, utilising multicentre and detailed clinical-imaging data. However, the small sample size, retrospective design, resulting lack of imaging data, and limited treatment outcomes represent significant limitations; conclusions regarding L-arginine efficacy are purely hypothesis-generating.

This study showed that SLE in genetically diagnosed mitochondrial diseases are most commonly observed in MELAS and POLG mutations. However, they may also develop in rare subtypes such as CoQ10 deficiency and Leigh syndrome. During episodes, the presence of bilateral cortical lesions on cranial MRI—often located in the frontotemporal regions and inconsistent with vascular distribution—and the detection of focal epileptiform activity on EEG were diagnostically significant findings. Clinical improvement was observed with iv L-arginine treatment initiated in the acute period. The findings emphasize that Stroke-like episodes should be considered in the differential diagnosis of sudden onset neurological findings in mitochondrial diseases.