0901 An odd presentation of a hidden curse

Abstract

Abstract Introduction Congenital central hypoventilation syndrome (CCHS) is a rare disorder of respiratory deficiency due to a mutation in the PHOX2B gene. Clinical presentation may be mild in certain individuals due to different levels of ventilatory dysregulation. Methods We present the findings of exogenous ventilatory challenge testing and polysomnography (PSG) performed on a normocapnic adult female with late-onset (LO) CCHS patient. Results The patient was exposed to four separate ventilatory challenges. During exposure to hyperoxia using 100% oxygen (O2) administration, patient showed an inconsistent ventilatory response with a blunted and delayed increase in regional tissue oxygen saturation (rSO2). During hyperoxic hypercapnia with 5% carbon dioxide (CO2) and 95% O2, she demonstrated a reduced ventilatory response based on respiratory rate and tidal volume. During hypoxic hypercapnia, 7% CO2 and 14% O2, patient demonstrated a delayed and markedly attenuated ventilatory response. Hypoxia; 100% nitrogen inhalation did not result in increased ventilation. Ve slope, change in minute ventilation/change in end-tidal CO2 (EtCO2), with hypercapnia challenges was 4.88, which is lower than normal. Ventilatory EtCO2 threshold was 36 mmHg. PSG showed apnea-hypopnea index 3.3 with hypoxemia during rapid eye movement (REM), with an oxygen saturation nadir of 84%. EtCO2 baseline was around 36, peak was 50 and was associated with REM-related apnea events. Arterial blood gas was unremarkable. Conclusion CCHS is characterized by abnormal respiratory response to exogenous ventilatory challenge testing. Hyperoxia silences peripheral chemoreceptors (PC) responsible for stimulating ventilation in normal individuals. Hyperoxic hypercapnia silences PC but stimulates central chemoreceptors (CC). Hypoxic hypercapnia stimulates hyperventilation via both PC and CC. Our patient demonstrated inconsistent and reduced ventilatory responses to all four challenges. As expected, the classic chemosensory parameter, Ve slope, for hypercarbia challenge was markedly reduced. However, the ventilatory EtCO2 threshold fell well below threshold typically observed in CCHS. PSG noted greater alveolar hypoventilation during REM compared to non-REM, which is also atypical for CCHS. In conclusion, exogenous ventilatory challenge testing demonstrated derangements in ventilatory control typical in CCHS. Despite this, our patient had no evidence of daytime hypoventilation with normal CO2 threshold. This case illustrates the phenotypic variability present in LO-CCHS. Support (if any)