Aims: Floppy infant syndrome (FIS) comprises of a group of disorders with a common symptom of generalized hypotonia at birth or in early life, which causes diagnostic challenge. In the current work, we aimed to describe the clinical and histopathological characteristics of FIS to help improve the diagnosis of this condition.
Methods: We collected information on the clinical characteristics, laboratory data, electrophysiological test results and detailed skeletal muscle biopsy histopathological features of 25 infants with FIS. We then discussed the final diagnoses and analyzed the neuromuscular features.
Results: Among the 25 infants with FIS, there were 7 cases of spinal muscular atrophy (SMA), 4 cases of congenital muscular dystrophy (CMD) (3 cases of merosin-deficient CMD and 1 case of Ullrich CMD), 8 cases of congenital myopathy (2 cases of central core disease, 1 case each of nemaline myopathy and centronuclear myopathy, and 4 cases of congenital fiber-type disproportion), and 6 cases of metabolic myopathy (3 cases of lipid storage myopathy, 2 cases of Pompe's disease, and 1 case of Leigh's syndrome). The histopathological characteristics of muscle biopsy were found to be distinct for these subgroups.
Conclusions: FIS is caused by a variety of neuromuscular disorders that have common clinical manifestations, including SMA, CMD, congenital myopathies and metabolic myopathies. Skeletal muscle biopsy is an essential tool for the definite and differential diagnoses of FIS, especially of neuromuscular origin.