Abstract Introduction Central Alveolar Hypoventilation Disorders are defined by inadequate ventilation during sleep, leading to elevated arterial carbon dioxide levels and reduced oxygenation despite structurally normal lungs and airways. Idiopathic central alveolar hypoventilation occurs in absence of pulmonary or neurologic disease, chest wall abnormalities, obesity, medication effects, or congenital hypoventilation syndromes. Report of case(s) 36-year-old male was referred to Sleep Medicine for elevated serum bicarbonate level (32 mmol/L) and respiratory acidosis on venous blood gas (pH 7.28, pCO2 63, HCO3 29) following Nephrology evaluation for foamy urine. Diagnostic polysomnography showed mild obstructive sleep apnea (AHI=7.2 events/hour, Nadir SpO2=90%) and elevated maximum transcutaneous PCO₂ (TcCO2) level of 59.4 mmHg. BMI=22.8 kg/m2 without history of cyanosis, developmental delay, or respiratory failure following anesthesia for colonoscopy. The patient returned for in-lab continuous positive airway pressure (CPAP) titration study, which demonstrated persistent nocturnal hypoventilation with baseline awake TcCO2=41 mmHg and maximum TcCO₂=55.9 mmHg with TcCO2 ≥ 55 mmHg for at least 10 minutes, despite normalization of oxygen saturation with CPAP. A comprehensive evaluation for hypoventilation revealed normal pulmonary function tests, brain MRI/MRA without structural or vascular abnormalities, and cardiopulmonary exercise testing (CPET) with a normal anaerobic threshold. Echocardiography showed normal systolic and diastolic function without pulmonary hypertension. There was unremarkable chest imaging, no endocrine abnormalities, and no use of respiratory-depressant medications. Patient underwent a Bilevel PAP (BPAP) titration study which resulted in normalization of TcCO₂ levels during sleep (Baseline TcCO2=39 mmHg, Maximum TcCO₂=40.5 mmHg) with normal oxygen saturations. The patient was initiated on BPAP 9/5 cmH2O for management of sleep-related hypoventilation. PHOX2B genetic testing was ordered but not completed due to cost. Conclusion This case highlights the importance of considering Idiopathic Central Alveolar Hypoventilation in adult patients with unexplained respiratory acidosis and nocturnal hypercapnia despite treatment of obstructive sleep apnea and in the absence of obesity, medication effect, cardiopulmonary, neurological, neuromuscular, chest wall or endocrine disorders following comprehensive diagnostic assessment. The patient’s response to BPAP therapy shows effectiveness of noninvasive ventilation in correcting the sleep-related hypoventilation. Although testing for PHOX2B gene mutation may be considered, timely initiation of appropriate therapy and close monitoring nevertheless remain essential. Support (if any)
Hassan et al. (Fri,) studied this question.