Obesity hypoventilation syndrome in a schizophrenic patient on antipsychotic medication: a case report

Schizophrenia patients on antipsychotic therapy, particularly second-generation antipsychotics (SGAs) like risperidone, face heightened risks of substantial weight gain and obesity due to multifactorial mechanisms including appetite dysregulation via hypothalamic pathways such as 5-HT2C receptor antagonism and neuropeptide Y upregulation. These metabolic disturbances can precipitate severe complications like obesity hypoventilation syndrome (OHS), characterized by BMI ≥30 kg/m², daytime hypercapnia (PaCO₂ >45 mmHg), and sleep-related breathing disorders after excluding other hypoventilation causes. We present a 27-year-old man with a 5-year history of paranoid schizophrenia who developed morbid obesity (BMI 58.8 kg/m²) following three years of risperidone therapy, manifesting as progressive dyspnea, excessive daytime sleepiness, orthopnea, snoring, and reduced functional capacity. Despite switching to long-acting injectable fluphenazine decanoate, he presented with acute-on-chronic respiratory failure evidenced by arterial blood gas showing pH 7.26, PaCO₂ 79 mmHg, PaO₂ 53 mmHg, HCO₃⁻ 35.5 mmol/L, and SaO₂ 81%, alongside tachycardia, tachypnea, and hypoxemia. Normal echocardiography, electrolytes, and thyroid function ruled out alternative etiologies. Diagnosed with OHS secondary to antipsychotic-induced obesity, he required 10 days of invasive mechanical ventilation in the ICU, with blood gases improving to pH 7.33, PaCO₂ 63 mmHg, and SaO₂ 99% by day 7. He declined bariatric surgery and home CPAP due to financial barriers, was discharged after 18 days following symptomatic relief, but failed follow-up and died upon readmission two months later with recurrent symptoms. This case underscores the critical need for baseline metabolic screening, vigilant monitoring (weight, BMI, lipids, glucose at 4-12 weeks and quarterly), and proactive interventions like lifestyle modifications, metformin, or antipsychotic switches to aripiprazole/ziprasidone to mitigate OHS risks. Early multidisciplinary management integrating PAP therapy and weight loss could avert fatal outcomes in this vulnerable population.