A 6-year-old girl with cerebral palsy undergoes selective dorsal rhizotomy surgery. The patient was born prematurely with a very low birth weight and had experienced periventricular cerebral white matter injury. During the procedure, dorsal rootlets of lumbosacral spinal nerves are selectively severed, as shown in the image below: Which of the following is the most likely effect of this intervention in this patient's lower extremities?

Question

A 6-year-old girl with cerebral palsy undergoes selective dorsal rhizotomy surgery.  The patient was born prematurely with a very low birth weight and had experienced periventricular cerebral white matter injury.  During the procedure, dorsal rootlets of lumbosacral spinal nerves are selectively severed, as shown in the image below:  Which of the following is the most likely effect of this intervention in this patient's lower extremities?

Quizplus · Accepted Answer

11ec160b_35a4_3d12_9249_8d2b90dbfce5_MD0001_00 This patient has cerebral palsy, a heterogeneous condition characterized by permanent, nonprogressive motor dysfunction caused by damage to the developing brain. Certain subtypes result in significant spasticity (eg, hypertonia, hyperreflexia). Spastic cerebral palsy may be caused by periventricular white matter necrosis (as in this patient), which leads to a loss of descending inhibitory control from the upper motor neurons. Specifically, lack of CNS inhibition leads to a hyperactive stretch reflex. The stretch reflex is a monosynaptic reflex mediated at the level of the spinal cord through the following pathway: The stretch reflex is responsible for deep tendon reflexes (eg, patellar, achilles) and the maintenance of muscle tone by constant muscular activity occuring even at rest, so a hyperactive stretch reflex leads to increased muscle tone (ie, spasticity). A selective dorsal rhizotomy procedure destroys the afferent (sensory) arm of the reflex arc, decreasing muscle tone without sacrificing motor innervation of the muscles. (Choices A, D, and E) Loss of lower motor neuron innervation can lead to paralysis, muscle atrophy, and fasciculations. However, by damaging only the dorsal nerve rootlets, the motor nerves (ventral) are spared. (Choice C) Deep tendon reflexes are manifestations of the stretch reflex caused by sudden stretching of the muscle. Because this reflex arc is interrupted by dorsal rhizotomy, the procedure results in decreased deep tendon reflexes as well as decreased muscle tone. Educational objective: Spasticity can be caused by the loss of descending inhibitory signals from upper motor neurons, leading to a hyperactive stretch reflex that results in increased muscle tone. Disruption of the afferent (sensory) arm of the stretch reflex through a selective dorsal rhizotomy can improve spasticity without causing paralysis. __________ References: Spasticity mechanisms - for the clinician. (http://www.ncbi.nlm.nih.gov/pubmed/21206767)

A 6-Year-Old Girl with Cerebral Palsy Undergoes Selective Dorsal Rhizotomy