CLINICAL CASE | Juvenile Motor Impairments
A 10-year-old boy first presented to his pediatrician with difficulty walking. He is an only child, of French-Canadian parents. His parents reported that recently he began to have difficulty standing still, is constantly shifting his position, and difficulty running. They reported normal motor development initially, but that now he seems clumsy. On examination, he was observed to have a wide-based gait with occasional shifting of position to maintain balance. Sitting and standing were noted to be associated with titubation. He was referred to a child neurologist who noted upper extremity ataxia, dysdiadochokinesia, and intention tremor. When the child was asked to maintain a standing posture with his eyes closed, he began to sway and lose his balance (positive Romberg sign). He had no tendon reflexes, such as the knee-jerk or biceps reflexes. An MRI was taken (Figure 13–1A; healthy person MRI, B). After his initial workup, he was seen regularly by his neurologist who noted a progression in his motor signs.
Answer the following questions based on your reading of the case, this chapter, and readings in prior chapters.
1. What is a positive Romberg sign and how is this related to the loss of tendon reflexes?
2. What are ataxia, intention tremor, and dysdiado-chokinesia?
3. What could account for the patient’s wide-based gait and ataxia?
4. What are the differences in the patient’s brain and spinal cord structure on MRI and that of a healthy person?
5. To what extent are the child’s motor impairments a reflection of damage to the cortical motor pathways?
Conclusion: After further workup and genetic testing, the child was diagnosed with Friedreich ataxia, a progressive spinocerebellar disease. Friedreich ataxia is an autosomal recessive disorder, due to a chromosome 9 mutation that, in virtually all cases, is an expansion of a GAA trinucleotide repeat within the gene that codes for the mitochondrial protein frataxin. In Friedreich ataxia there is a loss of lower extremity proprioception because of degeneration of large-diameter mechanoreceptive afferents. Friedreich ataxia patients often have cardiomyopathy, and most patients die as a result of cardiac arrhythmia or congestive heart failure. Key neurological signs and corresponding damaged brain structures Proprioceptive and reflex signs
The cervical spinal cord in the patient is thin compared with that of the healthy person. Thinning is produced primarily by degeneration of the central branches of the large-diameter somatic sensory afferents in the dorsal columns. However, the distal branches degenerate as well. Whereas the degeneration is accompanied by gliosis, it is insufficient to maintain the normal size of the spinal cord. With this large-diameter fiber loss, there is associated loss of tendon reflexes and limb proprioception. Patients with this sensory loss rely on vision to help maintain balance. This explains why, when the child’s eyes are closed, he is unable to maintain an upright posture. Patients also may have impaired tactile sensation. Unmyelinated fibers are spared. Ataxia
The loss of limb proprioceptive information ...