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Hypotonia is a condition of abnormally low muscle tone (the amount of tension or resistance to movement in a muscle), often involving reduced muscle strength.1 Hypotonia is not a specific neurological disorder, but a potential manifestation of many different diseases and disorders that affect motor nerve control by the brain or muscle strength (Table 30-1). Recognizing hypotonia, even in early infancy, is usually relatively straightforward, but diagnosing the underlying cause can be difficult and often unsuccessful. The long-term effects of hypotonia on a child's development and later life depend primarily on the severity of the muscle weakness and the nature of the cause. Some disorders have a specific treatment but the principal treatment for most hypotonia of idiopathic or neurological cause is physical therapy and/or occupational therapy to help the child compensate for the neuromuscular disability.
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Floppy Infant Syndrome
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Since hypotonia is most often diagnosed during infancy, it is also known as "floppy infant syndrome" or "infantile hypotonia" (Figure 30-1). Hypotonic patients may display a variety of objective manifestations that indicate decreased muscle tone. Infants with hypotonia have a floppy or "rag doll" appearance because their arms and legs hang by their sides and they have little or no head control. Motor skills delay is often observed, along with hypermobile or hyperflexible joints, drooling and speech difficulties, poor reflexes, decreased strength, decreased activity tolerance, rounded shoulder posture, with leaning onto supports, and poor attention and motivation. The extent and occurrence of specific objective manifestations depends upon the age of the child, the severity of the hypotonia, the specific muscles affected, and sometimes the underlying cause. Hypotonic infants often have difficulty feeding, as their mouth muscles cannot maintain a proper suck-swallow pattern, or a good breast-feeding latch. Hypotonia does not affect intellect. However, depending on the underlying condition, some children with low tone may develop language and social skills later in childhood.
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