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Phrenic nerves and diaphragms in sudden infant death syndrome
J Weis1, U Weber, J M Schröder
1Institute of Neuropathology, Technical University (RWTH), Aachen, Germany. weisj@patho.unibe.ch
Insights
Sudden infant death syndrome (SIDS) may involve respiratory muscle and nerve changes. While most SIDS infants show normal phrenic nerve and diaphragm development, some exhibit reduced nerve fiber density, potentially contributing to SIDS.
Area of Science:
- Neurology
- Pediatrics
- Pathology
Background:
- Respiratory system disturbances are implicated in sudden infant death syndrome (SIDS).
- The diaphragm, a major infant respiratory muscle, and its controlling phrenic nerve are poorly understood in SIDS.
- Investigating these structures may reveal critical factors in SIDS pathogenesis.
Purpose of the Study:
- To analyze morphometric and ultrastructural alterations in the phrenic nerve and diaphragm of SIDS infants compared to controls.
- To determine if developmental delays in these structures are present in SIDS cases.
Main Methods:
- Morphometric analysis of phrenic nerves and diaphragms from 24 SIDS infants and 7 controls.
- Electron microscopy to examine nerve fiber ultrastructure for neurofilament accumulations and other abnormalities.
- Comparison of muscle fiber diameters, axon cross-sectional areas, and myelin sheath thickness between SIDS and control groups.
Main Results:
- Phrenic nerve axons showed slightly larger cross-sectional areas but no increased myelin thickness in SIDS infants.
- One SIDS case presented with severely reduced myelinated nerve fiber density.
- SIDS diaphragms had significantly larger muscle fiber diameters, but widespread nonspecific ultrastructural changes (swollen axons/myelin, muscle fiber ruptures) were observed in both SIDS and control groups, necessitating cautious interpretation.
- Focal neurofilament accumulations were noted in nerve fibers of some SIDS infants.
Conclusions:
- While most SIDS infants show normal phrenic nerve and diaphragm development, reduced phrenic nerve myelinated axon density may contribute to SIDS in some cases.
- Widespread nonspecific ultrastructural findings require careful consideration when interpreting morphometric data.
- The study suggests that phrenic nerve and diaphragm development is not delayed in the majority of SIDS infants.
Abstract:
Disturbances of the respiratory system may be an important factor in the cascade of events leading to sudden infant death syndrome (SIDS). Even though the diaphragm is the major respiratory muscle in infants, little is known about alterations of this muscle and of the phrenic nerve in SIDS. In the present study, diaphragms and phrenic nerves of 24 SIDS infants and seven controls were analyzed. Morphometric analysis revealed only slightly larger cross sectional areas of phrenic nerve axons but no increase in myelin sheath thickness in SIDS cases. However, in one SIDS case, myelinated nerve fibre density was severely reduced. Using electron microscopy, several nerve fibres of SIDS infants showed focal accumulations of neurofilaments. Muscle fibre diameters in SIDS diaphragms were significantly larger compared to controls (P < 0.0001). However, in almost all SIDS and control cases, axons and myelin sheaths were artificially swollen, and acute segmental muscle fibre ruptures and contracture bands were found. These prominent nonspecific ultrastructural alterations should advise caution in the interpretation of morphometric data. Thus, in some cases exemplified by one case of the present series, decreased density of phrenic nerve myelinated axons might contribute to SIDS. Still, the present results indicate that development of phrenic nerves and diaphragms is not delayed in most SIDS infants.