The grade of acute thymus involution in neonates correlates with the duration of acute illness and with the percentage of lymphocytes in peripheral blood smear. Pathological study.

In various stressful conditions, the thymus is subjected to incidental involution, mostly due to the thymocytolytic effect of secreted glucocorticosteroids. The aim of this study was to examine acute thymic involution in sick neonates and to compare the morphological grade with some clinical and laboratory parameters. The influence of the illness on thymus tissue was investigated in 100 neonates who were treated and died in a neonatology intensive care unit. The preterm infants (n = 73) were born before the 37th week of gestation. Analysis of 57 placentas showed inflammation in 32% and circulatory disturbances in 23% of the cases. The causes of death were confirmed by autopsy: 35 were preterm infants with respiratory distress syndrome without infection, 22 were malformed, and 10 had birth trauma or asphyxia. In contrast, 29 of the preterm infants had an infection, mostly pneumonia or sepsis, and 4 of the term infants had such infections. Acute thymus involution was histologically graded (0-4) according to the method of van Baarlen (see text). Resting state (grade 0) was found in 25 of 38 neonates who lived <12 h. In 13 of 38 neonates who lived <12 h, thymus involution suggested prenatal stress. The grade of thymus involution related to the duration of illness (p < 0.001). Placental inflammation was associated with features of thymus involution (p < 0.048). Infection as a cause of death was connected to advanced thymus involution (p < 0.001). In preterm newborns, infection was more often connected with acute thymus involution than was respiratory distress syndrome (p < 0.003). Among the parameters measured in all available peripheral blood samples taken 24 h before death, only the lymphocyte count related to the grade of acute thymus involution (p < 0.05), with an increase in percentage of lymphocytes in peripheral blood smears from grade 0 to 2 and a decrease from grade 2 to 4. Although the white blood cell count is highly variable, a low percentage of lymphocytes might be a sign of advanced accidental thymus involution following acute stress. Copyright 2003 S. Karger AG, Basel