Optimal outcome in early-onset regressive autism: functional remission documented in a context of limited diagnostic access following a naturopathic intervention

Introduction: Autism spectrum disorder (ASD) is a neurodevelopmental condition characterised by high aetiological and clinical heterogeneity. In recent years, the need to investigate integrative approaches that account for its possible multisystemic nature has been increasingly recognised. From a complex systems perspective, effective interventions should be necessarily multidimensional and adaptive. Case presentation: A 3-year-old male participant of Chilean nationality was evaluated following a progressive sociocommunicative regression with complete loss of expressive language and onset of stereotypies. In the absence of standardised diagnostic tools, a neurologist established an informal clinical diagnosis of "autistic regression", documenting severe impairment across multiple neurodevelopmental domains (baseline ATEC: 83). Intervention: An individualised Naturopathic Complex Intervention (NCI) was applied over 24 months (July 2020 – July 2022), structured around three components: (1) trophology and dietary exclusion based on documented IgG hypersensitivities; (2) personalised naturopathic supplementation with analytical monitoring; and (3) parental coaching with structured home-based neurocognitive stimulation. Results: An 84.3% reduction in symptom severity was observed (ATEC: 83 → 13) over the 24 months of active intervention. External reassessment using the ADOS-2, conducted under blinded diagnostic conditions at month 17 of the NCI, ruled out ASD (total score: 6; classification: Non-ASD; symptom level: LOW). Long-term neurological follow-up via QEEG at age 8 documented a mild attentional-executive profile, consistent with high-functioning residual neurodivergence. Conclusions: The NCI was associated with a clinical trajectory consistent with functional remission (optimal outcome). The case illustrates, from a Latin American context with limited diagnostic access, that the absence of standardised baseline assessment tools does not preclude rigorous documentation of clinical evolution when validated follow-up metrics (ATEC), blinded external reassessments (ADOS-2) and objective neurological monitoring (QEEG) are appropriately combined. Additionally, the case documents how a prior diagnostic label can act as an interpretive lens modulating the conclusions of subsequent assessments, a phenomenon described in the literature as diagnostic overshadowing.