PHRENIC NERVES AND DIAPHRAGMS IN SUDDEN-INFANT-DEATH-SYNDROME

Disturbances of the respiratory system may be an important factor in t he cascade of events leading to sudden infant death syndrome (SIDS). E ven though the diaphragm is the major respiratory muscle in infants, l ittle is known about alterations of this muscle and of the phrenic ner ve in SIDS. In the present study, diaphragms and phrenic nerves of 24 SIDS infants and seven controls were analyzed. Morphometric analysis r evealed only slightly larger cross sectional areas of phrenic nerve ax ons 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 show ed focal accumulations of neurofilaments. Muscle fibre diameters in SI DS diaphragms were significantly larger compared to controls (P < 0.00 01). However, in almost all SIDS and control cases, axons and myelin s heaths were artificially swollen, and acute segmental muscle fibre rup tures and contracture bands were found. These prominent nonspecific ul trastructural alterations should advise caution in the interpretation of morphometric data. Thus, in some cases exemplified by one case of t he present series, decreased density of phrenic nerve myelinated axons might contribute to SIDS. Still, the present results indicate that de velopment of phrenic nerves and diaphragms is not delayed in most SIDS infants. (C) 1998 Elsevier Science Ireland Ltd.