Neuromuscular Junction Disorders and Floppy Infant Syndrome: A Comprehensive Review

Floppy infant syndrome, also sometimes referred to as rag-doll syndrome, is characterized by hypotonia that could present as either peripheral hypotonia or central. Depending on the origin of hypotonia, the infant will present with different symptoms that ultimately have the characteristic feature of hypotonia. The clinical examination is crucial in diagnosing floppy infant syndrome in the neonate period, but the most critical factor is investigating and diagnosing the underlying cause of hypotonia. Regardless of whether the underlying cause of hypotonia is peripheral or central in origin, the presentation of floppy infant syndrome focuses on observing for the presence or absence of specific signs such as 'frog-leg' posture, significant head lag on traction or pull-to-sit maneuver, or the feeling of 'slipping through the hands' when the infant is held under the arms. Infantile botulism, transient neonatal myasthenia gravis, congenital myasthenia gravis, hypermagnesemia, and aminoglycoside toxicity are all neuromuscular junction disorders that are considered to be a differential diagnosis of floppy infant syndrome. These neuromuscular junction disorders ultimately impact the presence of acetylcholine within the neuromuscular junction. While some of these disorders may impact the acetylcholine receptors, others may cause a depletion within the end-plate anticholinesterase enzyme. A deficiency within the anticholinesterase deficiency may cause desensitization to acetylcholine, which could also cause present with floppy infant syndrome as well. Depending on the underlying causative disorder leading to the presence of floppy infant syndrome, the treatment will vary considerably. Treatment of the underlying causative syndrome resulting in the presentation of floppy infant syndrome deals with the symptoms of hypotonia, and as a result, the decreased muscle tone, diminished tendon reflexes, any feeding or respiratory difficulties diminish.