Respiratory muscle testing is often limited to noninvasive volitional tests such as vital capacity and maximal static pressures. We report the case of a 12-year-old boy with congenital muscular dystrophy (CMD) in whom invasive and non-volitional respiratory muscle tests showed an elective diaphragmatic dysfunction with the preservation of expiratory muscle strength. This finding, coupled with a clinical phenotype associating diffuse muscle atrophy with finger hyperlaxity and proximal contractures, strengthened the suspicion of Ullrich CMD. Skin-cultured fibroblasts showed intracellular retention of collagen 6 (COL6), muscle magnetic resonance imaging was typical of COL6 myopathy, and molecular studies identified a COL6 gene mutation (COL6A2 c.954+2T>C). The diagnosis of a diaphragmatic dysfunction led to a sleep study that evidenced periods of hypoxemia which justified nocturnal noninvasive ventilation. This case report highlights the benefit of assessing respiratory muscles, through invasive procedure, to assist in clinical diagnosis and to guide clinical management.
Keywords: COL6-related myopathy; Ullrich congenital muscular dystrophy; diaphragm; respiratory function; vital capacity.