Atypical knee jerk responses in high-risk children: A longitudinal EMG-study
Elisabeth J M Straathof1, Elisa G Hamer2, Kirsten R Heineman3
1University of Groningen, Department of Paediatrics - Division of Developmental Neurology, University Medical Center Groningen, Hanzeplein 1, 9713 GZ, Groningen, the Netherlands.
Insights
Persistent tonic responses (TRs) in infancy predict cerebral palsy (CP) risk, but this association fades by school-age. Spinal hyperexcitability, indicated by TRs and reflex irradiation, generally decreases from infancy to childhood.
Area of Science:
- Neuroscience
- Developmental Pediatrics
- Neuromuscular Physiology
Background:
- Atypical knee jerk reflexes, including tonic responses (TRs), clonus, and contralateral responses, were previously linked to cerebral palsy (CP) in very high-risk (VHR) infants at 21 months.
- Understanding the pathophysiology of these atypical reflexes requires evaluating their persistence and association with CP into school-age.
Purpose of the Study:
- To investigate the association between infant atypical knee jerk responses and the presence of CP at school-age.
- To understand the developmental trajectory of spinal hyperexcitability markers from infancy to school-age.
Main Methods:
- Longitudinal assessment of 31 VHR children and 24 typically developing children from infancy to 7-10 years (school-age).
- Continuous surface electromyography (EMG) of thigh muscles during knee jerk responses in infancy and at school-age.
- Neurological examinations, including CP diagnosis and Gross Motor Function Classification System (GMFCS) assessment at corrected age and school-age.
Main Results:
- Persistent tonic responses (TRs) in infancy were associated with CP at school-age, though TR prevalence decreased and was not associated with CP at school-age.
- Clonus prevalence remained stable but was higher in children without CP than those with CP.
- Reflex irradiation, common in all school-age children, decreased in VHR children from infancy to childhood.
Conclusions:
- While TRs in infancy indicate an increased risk for CP, this association is not present at school-age.
- Spinal hyperexcitability, reflected by reflex irradiation and TRs, generally diminishes between infancy and school-age.
Introduction:
We previously found that atypical responses to the knee jerk reflex, i.e., tonic responses (TRs), clonus and contralateral responses in very high-risk (VHR) infants were associated with cerebral palsy (CP) at 21 months. The current study aimed for a better understanding of pathophysiology of atypical knee jerk responses by evaluating whether infant atypical knee jerk responses are associated with CP and atypical knee jerk responses at school-age.
Methods:
31 VHR-children, who had also been assessed longitudinally during infancy, and 24 typically developing children, were assessed at 7-10 years (school-age). We continuously recorded surface EMG of thigh muscles during knee jerk responses longitudinally during infancy and once at school-age. Neurological condition was assessed with age-appropriate neurological examinations. It included the diagnosis of CP at 21 months corrected age and school-age. CP's type and severity (Gross Motor Function Classification System (GMFCS)) were reported.
Results:
Persistent TRs in infancy were associated with CP at school-age. TR prevalence decreased from infancy to childhood. At school-age it was no longer associated with CP. Clonus prevalence in VHR-children did not change with increasing age; it was significantly higher in children without than those with CP. Reflex irradiation was common in all school-age children, and its prevalence in contralateral muscles in VHR-children decreased between infancy and childhood.
Conclusions:
In infancy, TRs indicated an increased risk of CP, but at school-age TRs were not associated with CP. In general, spinal hyperexcitability, expressed as reflex irradiation and TRs, decreased between infancy and school-age.
