Sanjiv Bhatia, M.D.
Rick Abbott, M.D.
Jeffrey Blount, M.D.
Nico Enslin, M.D.
Editor in Chief
Rick Abbott, M.D.
Childhood hypertonia is a relatively common disability encountered by the pediatric neurosurgeon. Over the past several decades, a number of treatment options have become available for its management. Key to the successful use of these treatments, however, is an understanding of the various forms of childhood hypertonia and the features that distinguish them.
There are three main types of childhood hypertonia: spasticity, dystonia, and rigidity (1). Spasticity is a velocity-dependent increase in resistance to movement of a muscle when it is passively stretched. It results from an interruption of the descending motor pathways that normally release GABA within the spinal cord. Common causes of spasticity include cerebral palsy and traumatic brain injury. Other causes include stroke, meningitis, and anoxic encephalopathy. Dystonia refers to involuntary, stereotypic patterns of limb movement with associated hypertonia that end in a fixed posture with sustained muscle contractions of a rigid nature (lead-pipe resistance to movement). When the limb is moved passively, the tone tends to decrease. Rigidity in children has been defined as “…the resistance to externally imposed joint movement…” that is present even at very low rates of movement and is not velocity dependent (1). Simultaneous co-contraction may be present as well as resistance to alteration in the direction of movement (1). No patterns of involuntary movement are seen in association with voluntary distal movement in a limb, and the limb does not tend to return to a fixed posture or extreme angle (1). Mixed hypertonia can also be seen in children; this term refers to hypertonia in a limb that has elements of spasticity and dystonia or other forms of non-velocity-dependent hypertonia.
- Spasticity is velocity dependent: A key feature of spasticity is its tendency to increase as the rate of muscle stretching increases. Repeated movement in a muscle will also then lead to increased spastic hypertonia.
- Rigidity is not velocity dependent: The resistance to passive movement in a muscle with rigidity is present regardless of the rate of the movement.
- Dystonia is a movement disorder: Dystonia is an involuntary contraction in a muscle that is associated with a voluntary movement. Dystonia typically has a twisting or distorting feature, and its intensity can fluctuate over time.
- Treatments of hypertonia are tone specific: The neurosurgical treatments for hypertonia are directed at elements of the neural circuitry involved in the type of hypertonia. As a consequence, each treatment is effective only for specific types of hypertonia and is typically ineffective in treating other forms of hypertonia. Knowledge of the type of hypertonia being targeted for treatment and which treatments are effective for it are key for successfully managing disorders of increased tone in children.
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