Background <p>Posttraumatic stress disorder (PTSD) is characterized by substantial heterogeneity in symptom presentation, illness trajectory, and treatment response, highlighting the need for objective approaches capable of monitoring treatment-related neurofunctional changes beyond conventional symptom-based outcomes. Functional near-infrared spectroscopy (fNIRS) is an increasingly used non-invasive neuroimaging technique that enables repeated assessment of cortical hemodynamics in clinically feasible settings. Although fNIRS has been widely applied to characterize neurofunctional alterations associated with PTSD, its potential role in monitoring longitudinal treatment-related brain changes has not been critically synthesized.</p> Methods <p>A narrative review was conducted using a structured search strategy across PubMed, Web of Science, Scopus, PsycINFO, and the Cochrane Library to identify studies published up to 30 January 2026. Studies were eligible if they included adults with PTSD or clinically significant trauma-related symptomatology and employed repeated NIRS/fNIRS assessments to evaluate neurofunctional changes associated with pharmacological or non-pharmacological therapeutic interventions.</p> Results <p>Four studies met the eligibility criteria and were included in the qualitative synthesis. Across the included studies, the non-pharmacological interventions consisted of trauma-focused psychotherapy, attention-based cognitive training, and equine-assisted services. No eligible longitudinal studies evaluating pharmacological treatments using repeated NIRS/fNIRS assessments were identified. Across studies, treatment was consistently associated with modulation of prefrontal cortical hemodynamic activity, although the direction and magnitude of neurofunctional changes varied according to intervention type, experimental paradigm, and methodological approach. Overall, the available evidence supports the feasibility of repeated fNIRS assessment while highlighting substantial methodological heterogeneity and the limited maturity of the current evidence base.</p> Conclusions <p>Current evidence suggests that fNIRS represents a promising and clinically feasible approach for monitoring treatment-related neurofunctional changes in PTSD and trauma-related symptomatology, particularly during non-pharmacological interventions targeting prefrontal regulatory processes. Rather than replacing established neuroimaging techniques such as functional magnetic resonance imaging, fNIRS should be considered a complementary tool that is particularly suitable for repeated assessments in real-world clinical settings. Future research should prioritize adequately powered longitudinal studies, standardized acquisition and analytical protocols, multimodal neuroimaging approaches, and the inclusion of pharmacological treatment trials to determine the potential of fNIRS as a candidate longitudinal neurofunctional biomarker of treatment response.</p> Clinical trial number <p>Not applicable.</p>