Evaluation of pupil diameter is described as a practical, useful, and non-invasive method for analyzing the autonomic nervous system [11]. For this purpose, objective measurements and evaluations of pupil reflexes can be made using automatic pupillometry, allowing analysis of sympathetic and parasympathetic system innervation through defined parameters [12]. Various analyses have been conducted across different disease groups, including bipolar disorder, Alzheimer’s disease, and age-related autonomic nervous system responses in healthy individuals, and the results have been used as objective criteria to assess the balance between the sympathetic and parasympathetic systems [9, 12,13,14,15]. In their study, Ramos et al. evaluated pupillary responses following T3 sympathectomy surgery and demonstrated the development of subclinical Horner's syndrome, which they associated with the anatomical proximity of the sympathetic chain to the oculosympathetic pathway [8]. In our study, there was no significant difference between the preoperative pupillometry measurements of the hyperhidrosis group and the control group. However, significant differences were observed in the latency of contractions and photopic low values between the preoperative and postoperative pupillometry measurements in the patient group, indicating increased parasympathetic system activity. This study, being one of the first on the subject, is significant in showing that the systemic effects of the ETS, a treatment for hyperhidrosis, can arise even though hyperhidrosis is a disease directly related to sweat glands. We believe that the sympathetic activity in the face might have decreased due to the level of sympathectomy. Therefore, we believe that comparing pupillometric responses in isolated T3 and isolated T4 sympathectomies in the following stages may provide additional insights into the topic.

Hyperhidrosis, although a benign disease, significantly affects the quality of life and therefore requires treatment. Although medical treatments, such as botulinum toxin, exist, the only permanent and definitive solution for patients without underlying diseases or conditions contraindicating surgery is thoracic sympathectomy [16, 17]. Additionally, surgical treatment is preferred due to its low morbidity and mortality, rapid recovery process, and immediate postoperative response [1]. In our clinical approach, we prioritize the social anxiety and professional life impact of hyperhidrosis when making treatment decisions. We also ensure the identification of the underlying pathophysiologies that might contribute to sweating and consult endocrinology and cardiology for the preoperative evaluation of rare postoperative complications such as arrhythmias. Postoperative hospital stay was 2 days, and only two patients required postoperative chest tubes and pleurovac placement, which aligns with the low morbidity seen in hyperhidrosis cases.

In patients with hyperhidrosis, the surgical success rate is evaluated based on symptom control and patient satisfaction. A review published in 2021 reported a 96% rate of symptom control and a 92% overall satisfaction rate for primary hyperhidrosis cases. It was noted that patient satisfaction decreased to 93.22% in the first postoperative evaluation, and by 12 months, it decreased further to 88.23% [18]. In Toolabi’s study, evaluating 10-year results, near-complete positive outcomes were observed in palmar hyperhidrosis cases, while satisfactory results were noted for craniofacial hyperhidrosis. However, in cases of pure axillary hyperhidrosis, results were poor enough to suggest discontinuing the surgical procedure [19]. In our study, when asked, “If we were to start the operation again, would you still choose to undergo it?”, all patients answered “yes.” The patient satisfaction rate was 95.8%. Only one patient expressed dissatisfaction, with the primary issue being compensatory sweating. In this patient, Grade 3 and widespread compensatory sweating occurred. However, symptom control was 100% in this patient. We believe that our strict patient selection criteria played an important role in achieving these results. In our clinical approach, all patients were classified as Grade 3 or 4, with the exception of seven patients with palmar–axillary hyperhidrosis involving the palms. Therefore, it can be stated that late-stage symptom control was maintained at the same rate due to the average follow-up period of 12 months.

In satisfaction assessments, although the surgical morbidity and mortality for hyperhidrosis are low, the primary cause of postoperative dissatisfaction in patients is compensatory sweating [20]. Compensatory sweating (CS) is the most common complication, occurring in 3–98% of cases. Predictors for CS include older age, higher body mass index, elevated body temperature, family history, and smoking, according to various publications [12, 21, 22]. While some studies suggest that patients under 25 are ideal surgical candidates, others report better outcomes in older patients, and yet others find no significant relationship [19, 21, 23, 24]. There are several hypotheses regarding the mechanism of compensatory sweating. It is suggested that when the sympathetic chain is cut, sweating attempts to compensate in other areas of the body, meaning the total amount of sweating does not change. Additionally, it is thought that the block of negative feedback signals following the severing of the sympathetic ganglion leads to increased sweating in other regions through augmented efferent signals [25, 26]. Despite varying group outcomes in our study, compensatory sweating was observed in 75% of cases, although it did not significantly affect patient satisfaction. The majority of patients with CS were in Group 1, and this did not substantially alter their satisfaction levels, which makes the results encouraging.

For effective hyperhidrosis treatment, it is necessary to target levels below T2, ideally including T3–4 levels, as the Kuntz fibers form at these levels and extend to the brachial plexus [27]. However, research has primarily focused on how patient risk factors, along with surgical factors, influence CS outcomes. A review published in 2008 suggested no relationship between sympathectomy level and CS, but all other studies found that blockage at levels lower than T2 leads to better CS outcomes and a significant improvement in quality of life [1, 25, 27,28,29,30,31]. In our study, all patients received T3 and commonly T3–4 sympathectomy, in line with the literature. Only one patient experienced Grade 3 widespread compensatory sweating, which can be seen as a positive reflection of performing sympathectomy further from T2.

The main value of our study lies in it being one of the first to evaluate the sympathetic system activation through non-invasive and objective pupillometry measurements, in relation to the effectiveness of hyperhidrosis surgery and CS levels. Additionally, the lack of differences in preoperative measurements between the hyperhidrosis and control groups supports the idea that specific sympathetic activity increases in sweat glands in the pathophysiology of sweating.

A major limitations of our study are the sensitivity of dynamic pupillometry measurements and the absence of long-term pupillometry results. Moreover, as only a T3-level sympathectomy was performed on all patients, it hindered the evaluation of the relationship between the level of sympathectomy and pupil response.

In conclusion, hyperhidrosis is a pathology that directly affects the sweat glands and is related to sympathetic activity. The findings from postoperative pupillometry, indicating increased sympathetic activity, demonstrate that although hyperhidrosis specifically affects the sweat glands, the surgery has a systemic effect on the body's overall sympathetic response. The results of this study, along with broader patient group data and further studies on pathogenesis and compensatory mechanisms, may yield more meaningful conclusions.