Lymphocytic reactions in childhood afford difficulties in interpretation because a predominance of lymphocytes and a greater lability of the blood-forming mechanism constitute normal features of this period. A marked increase in lymphocytes is a well known accompaniment of certain infections, such as pertussis, and of postinfectious states, while leukopenia with a relative increase in lymphocytes characterizes the blood reaction in typhoid fever and influenza. A lymphocytic increase may occur, however, in infants and children when a specific etiologic agent or a well defined clinical condition cannot be demonstrated.
Two types of conditions are encountered in young patients which are characterized by lymphocytosis and which are frequently confused with infectious mononucleosis, or even with leukemia. In one, transient, unexpected hyperleukocytosis with an absolute and a relative increase in lymphocytes occurs and is unassociated with recognizable symptoms or physical signs. The second type, which is more frequently encountered, follows infections of the
SMITH CH. INFECTIOUS LYMPHOCYTOSIS. Am J Dis Child. 1941;62(2):231–261. doi:10.1001/archpedi.1941.02000140002001
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