Pickwickian syndrome, or obesity hypoventilation syndrome (OHS), comprises the triad of obesity (BMI ≥30 kg/m2), daytime hypoventilation (awake hypercapnia and hypoxemia), and sleep-disordered breathing in the absence of alternative explanations (e.g. severe parenchymal lung disease, mechanical or metabolic abnormalities).
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Terminology
Being a separate disease entity it has to be distinguished from the combination of obesity and obstructive sleep apnea, as patients suffering from the latter two lack daytime hypercapnia and hypoxemia.
Epidemiology
While the exact prevalence is not known, 0.15-0.3% may be a good estimate. Due to the lack of routine screening, it may be underdiagnosed. The prevalence is assumed to be increasing.
Clinical presentation
Main presenting symptoms and signs may be as follows:
- severe upper airway obstruction
- hampered respiratory mechanics
- blunted central respiratory reflex
- pulmonary hypertension
Pathology
This syndrome arises from a complex interaction between sleep-disordered breathing, diminished respiratory drive, and obesity-related respiratory impairment.
The three leading hypotheses for the pathogenesis of chronic daytime alveolar hypoventilation in obesity hypoventilation syndrome consist of:
- hampered respiratory mechanics due to obesity
- central hypoventilation caused by leptin resistance
- pathologic compensatory response to acute hypercapnia
Radiographic features
Patients with obesity hypoventilation syndrome may either have normal chest radiographs or exhibit cardiomegaly and/or abnormal pulmonary vascularity, i.e. signs of pulmonary hypertension. Typically, subtle radiographic signs of pulmonary vascularity are difficult to evaluate given the patient body habitus.
Treatment and prognosis
Compared to obese patients, patients with obesity hypoventilation syndrome are prone to more severe obesity, congestive heart failure, angina pectoris, cor pulmonale, and secondary pulmonary arterial hypertension. In addition, they are more often hospitalized and on hospital admission more often admitted to intensive care units.
The mainstay of therapy comprises:
- positive airway pressure therapy
- bariatric surgery
- pharmacotherapy
History and etymology
The term "Pickwickian syndrome" was popularized by Dr CS Burwell in 1977 4, inspired by the similarities to the novel figure "fat boy" Joe in Charles Dickens' The Pickwick Papers 3.