The Ethics Committee of the Affiliated Hospital of Zunyi Medical University approved this study (Ethics Approval Number: KLLY-2021-022). This study retrospectively included 119 patients diagnosed with TBM who were hospitalized and treated at our institution between July 2020 and December 2022. Clinical data were obtained through a comprehensive review of electronic medical records. The diagnosis of TBM was made according to the criteria established by Suzaan Marais et al. (5). Patients were classified into three categories based on the diagnostic criteria: confirmed, highly probable, or possible cases. Confirmed cases fulfilled the clinical inclusion criteria and also met one or more of the following: (a) identification of antibiotic-resistant bacteria in cerebrospinal fluid (CSF), (b) positive MTB culture from CSF, or (c) detection of MTB nucleic acid in CSF. Highly probable cases met the clinical inclusion criteria and had a diagnostic score of ≥12 (or ≥10 in the absence of imaging), with at least 2 points derived from either CSF analysis or cranial imaging, and other differential diagnoses were excluded. Possible cases met the clinical inclusion criteria and had a diagnostic score between 6 and 11 points (or 6-9 in the absence of imaging); these cases did not undergo lumbar puncture or cranial imaging and could not be definitively confirmed or excluded as TBM.

Exclusion criteria encompassed a history of prior anti-tuberculosis treatment, intolerance to first-line anti-tuberculosis drugs, initiation of treatment more than one week before hospital admission, resistance to isoniazid (INH) or rifampin detected before or during treatment, elevated alanine aminotransferase (ALT) or creatinine levels beyond the upper limit of normal at treatment initiation, long-term use of immunosuppressive agents, severe underlying comorbidities, pregnancy or lactation, and other factors necessitating exclusion. These stringent criteria were applied to ensure the selection of a homogenous study population for assessing the influence of INH dosage and NAT2 gene polymorphism on the treatment outcomes of TBM. The patients were divided into two groups based on the prescribed INH dosage: the standard-dose group (300 mg/day) and the high-dose group (600 mg/day), comprising 32 patients and 78 patients, respectively.

The primary endpoint of this study was disability or mortality, while secondary endpoints included changes in clinical manifestations, laboratory parameters, and imaging findings. Comprehensive demographic data were collected for all participants, including gender, age, height, weight, smoking and alcohol use history, comorbidities, and disease duration. Clinical manifestations were systematically assessed, encompassing symptoms such as fever, headache, nausea, vomiting, cough, sputum production, weight loss, night sweats, focal neurological deficits, cranial nerve palsy, and altered mental status. Laboratory investigations included measurements of various parameters, including total white blood cell count, hemoglobin, blood glucose levels, lymphocyte count, and cerebrospinal fluid (CSF) characteristics, such as intracranial pressure, white blood cell count, lymphocyte count, protein concentration, chloride concentration, adenosine deaminase activity, and CSF-to-blood glucose ratio.

Microbiological diagnostics for Mycobacterium tuberculosis were performed through acid-fast staining of CSF, sputum, and bronchoalveolar lavage fluid, complemented by molecular assays such as Xpert MTB/RIF, LAMP, metagenomic next-generation sequencing (mNGS), and mycobacterial culture. Imaging studies included cranial and chest imaging, as well as examination of other relevant anatomical regions. The severity of TBM was assessed using the Glasgow Coma Scale (GCS) and the Medical Research Council (MRC) staging system (5).

Peripheral blood DNA from patients with TBM was extracted using the Lad-Aid824s blood genomic DNA extraction reagent (Xiamen Zhishan Biotechnology Co., Ltd.). Initially, a dithiothreitol (DTT) solution (1 mol/L) was prepared by dissolving 0.45 g of DTT in deionized water to a final volume of 3000 μL. The solution was mixed thoroughly, aliquoted into small portions, and stored at temperatures below -18°C to maintain stability. Subsequently, the Lab-Aid 824s/808 nucleic acid extraction instrument was powered on, and the initial interface appeared on the display screen. Reagent strips were placed on the instrument tray, and the sealing membrane was removed. Then, 200–500 μL of blood cell samples and 60 μL of the prepared DTT solution were added to the first well of each reagent strip. The tray was inserted into the instrument base and pushed into the instrument chamber. The “NA-DNA” program was selected, and the “Start” button was pressed to initiate the automated extraction process. Upon completion of the program, the tray was removed, and the eluted DNA was transferred to a centrifuge tube using a pipette. Finally, the concentration and purity of the extracted DNA were evaluated using a UV spectrophotometer. The acceptable range for the OD 260/OD 280 ratio was between 1.6 and 2.0, and the OD 260/OD 230 ratio was required to be ≥ 2.0. NAT2 genotyping was subsequently performed using real-time PCR combined with melting curve analysis.

All enrolled patients received treatment in accordance with the “2019 Chinese Central Nervous System Tuberculosis Diagnosis and Treatment Guidelines,” as issued by the Tuberculosis and Mycobacterial Diseases (TBM) Professional Committee of the Chinese Medical Association in July 2020. The anti-tuberculosis chemotherapy regimen consisted of a 3-month intensive phase with isoniazid, rifampin, pyrazinamide, and ethambutol (3HRZE), followed by a 9-month continuation phase with isoniazid and rifampin (9HR). The administration and duration of corticosteroid therapy adhered to the “2015 Chinese Tuberculosis Diagnosis and Treatment Guidelines” issued by the Chinese Medical Association. Follow-up was conducted through a comprehensive review of hospitalization records, outpatient consultations, and phone interviews. Data collected during follow-up included patients’ clinical symptoms post-discharge, subsequent treatments, prognosis, and survival status. The follow-up period ranged from 1 to 12 months, with a cutoff date of December 30, 2022. All patients successfully completed the follow-up process.

Statistical analyses were performed using SPSS 18.0 software. Categorical data were presented as [n(%)]. Continuous data were first tested for normality. Normally distributed data were expressed as mean ± SD, while non-normally distributed data were reported as median (P25, P75). Differences in categorical data between groups were analyzed using the chi-square test or Fisher’s exact test. For normally distributed continuous data, differences between two groups were compared using the independent sample t-test. For non-normally distributed continuous data, the Mann-Whitney U test was used. A significance level of α = 0.05 was set, with P < 0.05 considered statistically significant.

Based on the inclusion and exclusion criteria, a total of 119 patients with TBM who met the eligibility requirements were selected. Among these patients, the distribution of NAT2 gene polymorphisms was as follows: the IA type represented the largest proportion (approximately 61.3%), followed by the FA type (28.6%) and the SA type (10.1%), as shown in Figure 1 .

The cohort included 119 patients with TBM, with a higher proportion of males than females. The mean age was 42.13 ± 19.21 years, and the average body weight was 52.57 ± 7.96 kg. The mean disease duration was approximately 29.14 ± 44.45 days. Among the patients, 42% had comorbidities. Regarding the clinical classification, 34.5% were classified as confirmed cases, 35.3% as highly probable cases, and 30.3% as probable cases. The distribution of NAT2 genotypes was predominantly IA type, followed by FA and SA types, with IA type being the most common. Of the total patients, 32 (26.9%) were in the standard-dose group, while 87 (73.1%) were in the high-dose group. Detailed information is presented in Table 1 .

The baseline demographic data of patients with tuberculous meningitis (TBM), including gender, age, weight, disease duration, smoking history, alcohol consumption, and comorbidities, revealed no statistically significant differences between the standard-dose and high-dose treatment groups (P > 0.05), as summarized in Table 1 . The distribution of TBM manifestations at baseline showed that fever was present in 81 cases (68.1%), headache in 90 cases (75.6%), and nausea in 52 cases (43.7%). Other common symptoms included vomiting (49 cases, 41.2%), cough (53 cases, 44.5%), weight loss (21 cases, 17.6%), and night sweats (30 cases, 25.2%). Headache was the most prevalent symptom. However, no significant differences were found in the occurrence of fever, headache, nausea, vomiting, cough, weight loss, or night sweats between the two treatment groups (P > 0.05). These findings are further detailed in Table 2 .

Neurological manifestations were observed in a subset of patients, with 13 cases (10.9%) presenting with damage to the Stovea channel, 21 cases (17.6%) with cranial nerve palsy, and 33 cases (27.7%) with disability. Additionally, 32 patients exhibited altered consciousness, including 11 cases (9.2%) in a coma, 9 cases (7.6%) with hazy consciousness, 7 cases (5.9%) of lethargy, 3 cases (2.5%) of drowsiness, and 2 cases (1.7%) of delirium. Meningeal irritation was observed in 41 cases (34.5%). The severity of meningitis was graded as stage I in 83 cases (69.7%), and 83 cases (69.7%) had a Glasgow Coma Scale (GCS) score ≥ 15. Notably, damage to the Vesta meridian was significantly higher in the standard-dose group (21.9%) compared to the high-dose group (6.9%) (P = 0.046). However, cranial nerve palsy, altered states of consciousness, and meningeal irritation did not show significant differences between the groups (P > 0.05). Similarly, no significant differences were found in the severity of meningitis or GCS scores between the standard-dose and high-dose groups (P > 0.05). These findings are presented in Table 3 .

The analysis of cerebrospinal fluid (CSF) indicators, including intracranial pressure, white blood cell count, lymphocyte percentage, protein concentration, adenosine deaminase (ADA), CSF-to-plasma glucose ratio, glucose concentration, and chloride concentration, revealed no significant differences between the standard-dose and high-dose groups (P > 0.05). Additionally, no statistically significant differences were observed in the baseline CSF or pulmonary pathogen positivity rates between the two groups (P > 0.05) ( Table 4 ). Imaging results at baseline showed hydrocephalus in 22 cases (19.8%), enhanced anterior basal cistern density in 4 cases (3.6%), basal cistern meningeal enhancement in 26 cases (23.4%), tuberculomas in 27 cases (24.3%), and infarction in 28 cases (25.2%). Chest CT scans revealed secondary pulmonary tuberculosis in 62 cases (52.1%) and hematogenous disseminated pulmonary tuberculosis in 32 cases (26.9%). Imaging findings in other body parts, aside from the brain and lungs, were noted in 18 cases (15.1%). No significant differences were found in head imaging, chest CT, or imaging of other body parts between the standard-dose and high-dose groups (P > 0.05). These results are outlined in Table 5 .

Follow-up imaging results showed improvement in 26 cases (57.8%) of brain imaging and 40 cases (62.5%) of chest imaging. During the follow-up period, 40 patients in the standard-dose group and 25 patients in the high-dose group experienced disabling deaths by March, with the majority of deaths occurring at the conclusion of the intensive treatment phase. The differences in disability and mortality between the groups at the end of the 3-month intensive treatment period were statistically significant (P = 0.011). Similarly, at the 12-month follow-up, a significant difference in disability and mortality rates was observed between the two groups (P = 0.001). However, no significant differences were found in the improvement of cranial or chest imaging findings between the groups at the 3-month follow-up (P > 0.05). Detailed information is presented in Table 6 .

In terms of disability and mortality rates, the standard-dose group included 32 cases, of which 13 resulted in disability or death, while the high-dose group included 87 cases, with 12 instances of disability or death. The disability and mortality rate in the high-dose group (48.0%) was significantly lower than that in the standard-dose group (52.0%), with a statistically significant difference (P = 0.001). A detailed breakdown of these findings is presented in Table 7 . Further analysis of NAT2 genotypes revealed that within the standard-dose group, the SA genotype was associated with the lowest disability and mortality rates. In contrast, in the high-dose group, the FA genotype exhibited the lowest disability and mortality rates. However, no statistically significant differences in disability and mortality rates were observed between the FA, IA, and SA genotypes within both the standard-dose and high-dose groups. Detailed genotype-specific data can be found in Supplementary Table 1 .

In the comparative analysis of disability and mortality rates among FA, IA, and SA genotypes, no significant differences were observed between the non-disability/non-mortality group and the disability/mortality group (P > 0.05), as detailed in Supplementary Table 2 . When comparing disability and mortality rates between the standard-dose and high-dose groups for these genotypes, a statistically significant difference was found only in the IA type. Specifically, the disability and mortality rate in the standard-dose group (46.2%) was significantly higher than in the high-dose group (13.3%) (P = 0.019). However, no such differences were observed for the FA and SA types between the two dosage groups. Further details are provided in Supplementary Table 3 .