This patient has severe obesity (BMI, 49.2 kg/m2), headaches likely due to hypercapnia, unrefreshing sleep, evidence of cor pulmonale, secondary erythrocytosis due to chronic hypoxia, and Malampati class 4 airway with nocturnal desaturations. Therefore, the most probable diagnosis is OHS, which is defined as a combination of obesity (ie, BMI ≥ 30 kg/m2) and awake chronic hypercapnia (ie, PaCO2 > 45 mm Hg) accompanied by sleep-disordered breathing, usually severe OSA syndrome.3 If left untreated, patients with OHS can develop pulmonary hypertension and cor pulmonale.4 Patients with OHS have an elevated serum bicarbonate level due to the metabolic compensation for the chronic respiratory acidosis.5 Compared with patients with similar degrees of obesity, patients with OHS have increased medical resource utilization and are more likely to be hospitalized and require intensive care monitoring. Pulmonary hypertension is more common and more severe in patients with OHS than in those with OSA syndrome (50% versus 15%, respectively).6 It is essential for clinicians to maintain a high index of suspicion for OHS, particularly because early recognition and treatment improve outcomes. Polycythemia vera, a myeloproliferative disorder, is less likely in this case because it typically involves elevated hematocrit and splenomegaly in the absence of chronic hypoxemic stimulus to erythropoietin production. Pulmonary fibrosis would be expected to cause a restrictive ventilatory defect, along with hypoxia and, in severe cases, cor pulmonale. The absence of velcro crackles and normal lung examination and clear lung fields in this patient along with relatively preserved DLCO further rules out the diagnosis of pulmonary fibrosis. This patients normal thyroid examination and resting heart rate (102 bpm) argue against profound hypothyroidism; however, further biochemical testing is needed to rule this out.
3. Olson AL, Zwillich C. The obesity hypoventilation syndrome. Am J Med 2005;118:948–56.
4. Ahmed Q, Chung-Park M, Tomashefski JF Jr. Cardiopulmonary pathology in patients with sleep apnea/obesity hypoventilation syndrome. Hum Pathol 1997;28:264–9.
5. Pérez de Llano LA, Golpe R, Ortiz Piquer M, et al. Short-term and long-term effects of nasal intermittent positive pressure ventilation in patients with obesity-hypoventilation syndrome. Chest 2005;128:587–94.
6. Atwood CW Jr, McCrory D, Garcia JG, et al; American College of Chest Physicians. Pulmonary artery hypertension and sleep-disordered breathing: ACCP evidence-based clinical practice guidelines. Chest 2004;126(1 Suppl):72S–77S.
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