Case
A 12-month-old Japanese boy with interstitial lung disease was transferred to our hospital due to progressive respiratory failure despite receiving systemic corticosteroids, including methylprednisolone pulse therapy. He was born at full term from nonconsanguineous parents. His past medical history was only significant for mild motor developmental delay. Family history revealed that his father was undergoing further investigation of a chest X-ray abnormality. On admission, vital signs were remarkable for tachypnea and hypoxia. The respiratory rate was 50/min. SpO2 was variable between 90-95% with oxygen supplementation at 2 L/min via a nasal cannula. His height and weight were 74.0 cm (50th percentile) and 8.1 kg (10th percentile), respectively. He showed moderate intercostal retraction. Respiratory distress worsened even after the second methylprednisolone pulse therapy. A week after admission, his respiratory rate increased to 70/min, and his oxygen requirements were up to 3 L/min to maintain SpO2 >90%. HCQ was administered orally to improve his respiratory condition. In the eventual case of unresponsiveness, we discussed lung transplantation with his parents and consulted a transplant surgeon. Because SpO2 with the conventional nasal cannula varied greatly depending on his activity, such as sleeping or moving, we used HFNC (Optiflow™ junior, OPT316, Fisher & Paykel Healthcare Co. Ltd., Auckland, New Zealand) with an inspiratory oxygen fraction of 0.60 and flow rate of 15 L/min to accurately monitor his oxygenation. The inspiratory oxygen fraction was adjusted to maintain SpO2 ≥95%. Because the SpO2 variation dramatically decreased with HFNC, we were able to evaluate his oxygenation more accurately. After two weeks of HCQ administration, his oxygen requirements gradually decreased. At that time, SFTPC sequencing revealed a known pathogenic variation (c. 218T>C, p. Ile73Thr). His respiratory distress improved so that we could change the HFNC to a conventional nasal cannula after five weeks of HCQ treatment. Corticosteroid therapy was carefully tapered because he temporarily experienced adrenal insufficiency. Four months after admission, he was discharged with home oxygen therapy and treatment with HCQ, hydrocortisone, and azithromycin. The biochemical parameters of lung injury, such as lactate dehydrogenase (LDH) and Krebs von den Lungen-6 (KL-6), fluctuated during the course of inpatient treatment. The decrease in these parameters did not parallel with his clinical improvement (Figure 1). Radiological findings also improved several months after the clinical improvement.