199 Summary and discussion Limitations and strengths Several limitations and strengths of the studies conducted for this thesis have been delineated in their respective chapters; however, some overarching considerations warrant mention. One limitation is the small sample size, which is a consequence of the study’s experimental nature, highly specific setting, and specialized patient population. This leads to low statistical power, potentially affecting the generalizability of our results. Additionally, the open-label provision of DBS could introduce placebo effects or other non-specific influences on the outcomes. Factors such as increased patient contact, the novelty of participating in a unique study, and patients’ hope and expectations could inadvertently contribute to more positive results. We attempted to mitigate these limitations by incorporating a one-year follow-up period to investigate the durability of observed effects. Ethical considerations related to performing an invasive, experimental procedure on a medically vulnerable patient population necessitated the absence of a control group. Patient selection in our study deserves particular attention. Participants were critically ill, displaying chronic, treatment-resistant AN. Previous pharmacological and psychotherapeutic interventions had proven ineffective, and the patients were functionally impaired in virtually all life domains. Preoperatively, they were in dire physical condition, severely underweight, and experiencing both acute and long-term complications from enduring malnutrition. With an average illness duration of 21 years, this cohort can be classified as chronic. Therefore, our findings are applicable exclusively to this narrow, severely affected patient subgroup and not to the broader population of individuals with AN. Moreover, our study did not differentiate between AN subtypes (i.e., restrictive or binge-purge), and participants exhibited a range of psychiatric comorbidities. Given these factors, the generalizability of our findings is limited. On the one hand, it seems prudent to reserve new and experimental interventions for patients who have not responded to existing, standard treatment modalities - essentially, patients with limited options remaining. On the other hand, this specific patient population, characterized by treatment resistance and illness durations exceeding 10 years, inherently has a diminished likelihood of responding positively to any form of intervention. Moreover, the precarious physical and psychological condition of this patient group elevated the risk of adverse events, not just perioperatively but throughout the duration of the study. This was evidenced by the elevated incidence of (severe) adverse events we observed. As a result, the anorexia nervosa (AN) patients participating in our study required considerably more frequent and intensive medical oversight, both in inpatient and outpatient settings, compared to patients with OCD who were treated with DBS.
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