Beyond Airway Clearance: Specific Antibody Deficiency as a Driver of Refractory Sinopulmonary Disease in Primary Ciliary Dyskinesia

Background Primary ciliary dyskinesia (PCD) management relies on mucociliary clearance to prevent bronchiectasis. While humoral immunodeficiencies have been reported in PCD, their clinical significance remains under-defined. We hypothesize that co-occurring specific antibody deficiency (SAD) creates a “refractory phenotype” where mechanical clearance alone is insufficient, necessitating additional treatment. Case Description We describe three pediatric patients with PCD, defined by genetics or persistent low nasal nitric oxide, who experienced recurrent exacerbations despite adherence to maximal airway clearance. Patient 1 (13-year-old female) developed recurrent and severe pneumonias 1–2 times per year and chronic wet cough, leading to suspicion for PCD. Testing revealed duplicate low nNO, although PCD genetics and cilia brushings were unrevealing. Immune evaluation revealed low IgA and non-protective pneumococcal titers, requiring immunoglobulin replacement therapy (IGRT). Patient 2 (18-year-old female) presented with congestion since birth and multiple episodes of pneumonia. The diagnosis of PCD was made by low nNO and genetic testing positive for two pathogenic mutations in CCDC65. Despite aggressive clearance and antibiotic prophylaxis, she had multiple admissions for breakthrough infections and declining pulmonary function. Workup revealed non-protective pneumococcal titers despite adequate vaccination. Initiation of IGRT and antibiotic prophylaxis improved her clinical status. Patient 3 (17-year-old female) presented with chronic cough, sinusitis, and pneumonias from encapsulated organisms, frequently requiring intravenous antibiotics. She was found to have bronchiectasis and low nNO, nondiagnostic ciliary biopsy, and genetic testing confounded by chimerism. Inadequate post-booster pneumococcal titers suggested concomitant SAD that improved following initiation of antibiotic prophylaxis. Discussion These cases illustrate a unique phenotype of “treatment-refractory” PCD, characterized by breakthrough infections despite optimal clearance, warranting immune evaluation. All three patients were diagnosed with SAD and are routinely monitored for evolving humoral defects. Mechanical clearance addresses the mucociliary defect but fails to compensate for the lack of opsonization in concomitant SAD. Identification of this comorbidity allowed for targeted therapy (IGRT, prophylactic antibiotics) to stabilize pulmonary decline and improve quality of life. Thus, we recommend screening for humoral defects in PCD patients with recurrent infections despite adequate PCD supportive care.