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Extensive somatosensory innervation in infants with obstetric brachial palsy
A J Colon1, J W Vredeveld, G Blaauw
1Department of Neurology, Atrium, Medical Center, Heerlen, The Netherlands. dutcholon@netscape.net
Insights
Routine electromyography for obstetric brachial palsy (OBP) can be misleading. Somatosensory evoked potentials (SSEP) reveal intact sensory pathways in infants with OBP, suggesting a more diverse hand innervation than previously understood.
Area of Science:
- Pediatric Neurology
- Neurophysiology
- Developmental Neuroscience
Background:
- Routine electromyography (EMG) in infants with obstetric brachial palsy (OBP) often overestimates functional recovery compared to surgical findings.
- This discrepancy highlights the need for alternative diagnostic methods to assess sensory pathway integrity in OBP.
Purpose of the Study:
- To investigate the sensory innervation in infants diagnosed with obstetric brachial palsy (OBP).
- To evaluate the utility of somatosensory evoked potentials (SSEP) in assessing peripheral sensory pathways in OBP infants.
- To explore the diversity of segmental sensory innervation in the infant hand.
Main Methods:
- Somatosensory evoked potentials (SSEP) were recorded in 3- to 7-month-old infants with OBP affecting upper trunk or C5-C7 nerve roots.
- Stimulation of the thumb and middle finger was performed, with N20 cortical responses measured.
- Infants selected had no observed clinical improvement in biceps brachii and deltoid muscles.
Main Results:
- A normal N20 response, indicating functional peripheral sensory pathways, was evoked in most infants.
- Sensory signals from the thumb bypassed the upper trunk and C5-C6 roots, while signals from the middle finger bypassed the middle trunk and C7 root.
- These findings demonstrate the presence of sensory pathways extending to the thalamus and cerebral cortex.
Conclusions:
- Somatosensory evoked potentials (SSEP) provide valuable insights into sensory pathway integrity in infants with OBP.
- The study suggests a more complex and diverse segmental sensory innervation of the infant hand than traditionally described.
- SSEP can identify preserved sensory function despite severe motor deficits in OBP.
Abstract:
In the pre-operative screening of infants with obstetric brachial palsy (OBP), the results of routine electromyography are often overly optimistic when compared to the peri-operative findings. This prompted us to include investigation of the sensory innervation of these infants using the N20 (the first cortical response to a peripheral stimulation) of the somatosensory evoked potentials (SSEP). Three to seven months after birth, SSEP were recorded at the skull after stimulation of the thumb and middle finger in infants with obstetric rupture of the upper trunk or avulsion of roots C5, C6, or C7, and in whom no clinical improvement of motor function was observed in the biceps brachii and deltoid muscles. In most infants, a normal N20 could be evoked, indicating the existence of peripheral sensory pathways. From the thumb, these sensory pathways would necessarily bypass the upper trunk and dorsal roots of spinal nerves C5 and C6, and from the middle finger bypass the middle trunk and dorsal root C7, before extending into the dorsal column and projecting toward the thalamus and cerebral cortex. These data suggest that in infancy the segmental sensory innervation of the hand is more diverse than is described in most textbooks.