A62-13 Characterizing Respiratory Mechanics in TBCK Syndrome Using Impulse Oscillometry

Introduction TBCK syndrome is an ultrarare autosomal recessive neurodevelopmental disorder, with approximately 100 cases reported worldwide. It is characterized by global hypotonia, developmental delay, and progressive motor impairment. Respiratory insufficiency is a frequent comorbidity, but pulmonary mechanics remain poorly defined. Impulse Oscillometry (IOS) provides an effort-independent means of assessing airway resistance and reactance and is particularly useful in neuromuscular and pediatric populations. This report describes the use of IOS to characterize respiratory mechanics and bronchodilator response in two children with TBCK syndrome. Case Descriptions Two female patients (n = 2, [TBCK (c.376C>T (p.Arg126*)]), aged 7 years (Case A) and 10 years (Case B), underwent IOS testing using the Resmon PRO FULL V3 (Restech Srl, Italy), following ATS/ERS standards. Parameters included total and expiratory resistance (Rrs5Hz), reactance (Xrs5Hz), frequency dependence (R5-R19), and inspiratory-expiratory reactance difference (ΔXrs). Predicted reference values were derived from Dellacà et al., Eur Respir J, 2004. Both patients exhibited elevated total and expiratory Rrs5Hz, indicating increased airway resistance, with a partial bronchodilator response (30-38% decrease) suggesting reversible airway obstruction superimposed on restrictive mechanics. Xrs5Hz values were markedly negative before and after bronchodilator, consistent with low lung compliance. Frequency dependence of resistance and reactance improved modestly after bronchodilator, indicating heterogeneous ventilation. Importantly, ΔXrs values remained within the normal range, confirming the absence of expiratory flow limitation both before and after bronchodilator. Discussion This is the first report to describe airway mechanics in TBCK syndrome using Impulse Oscillometry. Both cases reveal a mixed ventilatory profile dominated by restriction and reduced compliance, accompanied by partial reversibility of airway resistance. These preliminary findings suggest that, beyond neuromuscular weakness, peripheral airway dysfunction and mild reversible obstruction may contribute to respiratory symptoms in TBCK. The use of IOS provided valuable, noninvasive insight into lung function without requiring patient effort, highlighting its utility in the evaluation and longitudinal monitoring of children with rare and neuromuscular disorders.