Thin ribs on chest X-ray: a useful sign in the differential diagnosis of the floppy newborn.

The significance of thin ribs among 26 newborns diagnosed as having neuromuscular disease is discussed. 19 had a chest X-ray. Thin ribs were observed in three of seven with congenital myotonic dystrophy, in two of four with myotubular myopathy and in one of five with spinal muscular atrophy. The ribs were normal in one case of nemaline myopathy and two cases of non-specific myopathy. Polyhydramnios was recorded in four of the six cases with thin ribs. Ventilatory support frequently was required for these infants. The observation of thin ribs on X-ray is highly suggestive of neonatal neuromuscular disease, and is neither specific for nor invariable in congenital myotonic dystrophy.