Respiratory insufficiency and sleep impairment in facioscapulohumeral muscular dystrophy.

Respiratory involvement in facioscapulohumeral muscular dystrophy is a clinically relevant yet frequently underdiagnosed. Manifestations range from subclinical restrictive ventilatory impairment to sleep-disordered breathing and nocturnal hypoventilation, and contribute to reduced quality of life as well as increased morbidity and mortality. Restrictive patterns occur in approximately 10-45 % of patients and are primarily associated with early disease onset, greater clinical severity, spinal deformities, and loss of ambulation. Pathophysiology is multifactorial, involving respiratory muscle weakness, reduced chest wall compliance, upper airway instability, and sleep-related reductions in ventilatory drive. Importantly, sleep-disordered breathing may arise independently of overall motor impairment and can represent the earliest clinically relevant manifestation. Given the often clinically inapparent presentation, structured respiratory investigation is recommended. Spirometry with upright and supine forced vital capacity remains central to evaluation and should be complemented by blood gas analysis, respiratory muscle testing and nocturnal carbon dioxide monitoring. Management follows established neuromuscular principles: non-invasive ventilation is indicated for hypoventilation or hypercapnia, whereas continuous positive airway pressure is appropriate for isolated obstructive sleep apnoea. Early recognition through systematic screening is critical to enable timely intervention and optimize outcomes.